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We report state-of-the-art first-principles molecular dynamics results on the heterogeneous chemical uptake of NO2, a major anthropogenic pollutant, on the dry and wet hydroxylated surface of α-quartz, which is a significant component of silica-based catalysts and atmospheric dust aerosols. Our investigation spotlights an unexpected chemical pathway by which NO2 (i) can be adsorbed as HONO by deprotonation of interfacial silanols (i.e., –Si–OH group) on silica, (ii) can be barrierless converted to nitric acid, and (iii) can finally dissociated to surface bounded NO and hydroxyl gas phase radicals. This chemical pathway does not invoke any previously experimentally postulated NO2 dimerization, dimerization that is less likely to occur at low NO2 concentrations. Moreover, water significantly catalyzes the HONO formation and the dissociation of nitric acid into surface-bounded NO and OH radicals, while visible light adsorption can further promote these chemical transformations. This work highlights how water-restricted solvation regimes on common mineral substrates are likely to be a source of reactive oxygen species, and it offers a theoretical framework for further and desirable experimental efforts, aiming to better constrain trace gases/mineral interactions at different relative humidity conditions. [ABSTRACT FROM AUTHOR]

A low-cost differential optical absorption spectroscopy (DOAS) spectrometer has been calibrated using a hybrid approach in which multiple absorption cross sections (ACSs) are measured and compared with previously obtained ACSs. The ACSs obtained from the measurement in this study are referred to as precise measurement (PM) ACSs, while those obtained from the simulation are referred to as hybrid simulation (HS) ACSs. The compact UV grating spectrometer was used to measure PM ACSs at different pressures and temperatures ranging from 295.75 K to 298.15 K. The spectral range was 230–320 nm with a spectral resolution of 0.28–0.39 nm. Uncertainties were evaluated and traceable to SI units. The relative standard measurement uncertainty of the PM ACS for o-xylene, p-xylene, SO2, benzene, styrene and toluene were 3.1 %, 3.1 %, 3.1 %, 3.0 %, 3.0 % and 2.9 %. respectively. This combined relative standard uncertainty includes contributions from optical path length (1.4 %), CRM concentration (≤0.74 %), absorbance repeatability (≤1.5 %), pressure (0.78 %) and temperature (2.1 %). ACSs for reactive trace gases without CRMs were derived using the HS method. This involved convolving literature spectra with measured instrumental functions (IFs) and subsequently applying spectral fitting to achieve ACSs that are well-aligned with those that would be obtained if measured with this spectrometer. The uncertainty of the HS ACSs results from the referenced ACSs, the determination of the IFs and the fitting procedures. The uncertainty of the referenced ACSs is taken directly from the literature and ranges from 0.05 % for benzaldehyde and formaldehyde to 5 % for oxygen. The uncertainty of the IFs is 0.67 %, 0.74 % and 0.65 % in regions I, II and III respectively. The total uncertainty for HS ACS is estimated to be 0.25 % for benzaldehyde, 1.01 % for NO2, 0.95 % for formaldehyde, 0.75 % for p-cresol, 0.74 % for m-xylene, 4.13 % for phenol, 4.19 % for ethylbenzene, 2.83 % for ozone in region I, 3.51 % for ozone in region II, 5.24 % for oxygen in region I and 5.31 % for oxygen in region II, taking into account the above uncertainty components. In a laboratory measurement of a gas mixture (benzene, toluene and ortho-xylene), the difference between the measurement values of the certified reference material (CRM) produced by the gravimetric method and the DOAS measurement is 8.5 % for benzene, 1.6 % for toluene and 4.9 % for ortho-xylene. Therefore, the uncertainty of the DOAS system was estimated to be 15.2 % for benzene, 8.2 % for toluene and 11.6 % for o-xylene, taking into account the uncertainties of the ACS (≤3.1 %), the fitting procedure (≤0.6 %), the difference with the CRM value (≤8.5 %) and the path length (1.4 %). In general, the system is ready for use in field measurements using the long-path DOAS technique. [ABSTRACT FROM AUTHOR]

The Environmental Trace Gases Monitoring Instrument (EMI-II) onboard the Chinese GaoFen-5B (GF5B) and DaQi-1 (DQ1) satellites is the successor of the previous EMI onboard the Chinese GaoFen-5 (GF5) satellite, and has a higher spatial resolution and a better signal-to-noise ratio. The GF5B and DQ1 were launched in September 2021 and April 2022, respectively. As part of China's ultraviolet-visible hyperspectral satellite instrument series, the EMI-II aims to conduct network observations of pollution gases globally in the morning and early afternoon. In this study, NO2 data were retrieved from the EMI-II payloads on the GF5B and DQ1 satellites using the Differential Optical Absorption Spectroscopy (DOAS) algorithm. The two satellites were consistently compared, and the results showed strong consistency on various spatial and temporal scales (R2 > 0.8). In four representative regions worldwide, NO2 data from the EMI-II exhibited good spatial consistency with those from the TROPOMI. The correlation coefficient (R2) of the total vertical column density (VCD) between the EMI-II and TROPOMI exceeded 0.85, and that of the tropospheric NO2 VCD exceeded 0.57. Compared with single-satellite observations, the dual-satellite network of the GF5B and DQ1 can effectively increase the observation frequency. On a daily scale, dual-satellite observations can reduce the impact of cloud coverage by 6–8% compared to single-satellite observations, and there are two valid observations of nearly 50% of the world's regions. Additionally, the differences between the two satellites can reflect the NO2 diurnal variations, which demonstrates the potential for studying pollutant gas diurnal variations. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) is a key substance in atmospheric chemistry, influencing the formation and destruction of tropospheric ozone and the atmosphere's oxidizing capacity. It also affects the physiological functions of organisms. NO is produced, consumed, and emitted by soils, the effects of soil NO concentrations on microbial C and N cycling and associated trace gas fluxes remain largely unclear. This study describes a new automated 12-chamber soil mesocosm system that dynamically changes incoming airflow composition. It was used to investigate how varying NO concentrations affect soil microbial C and N cycling and associated trace gas fluxes under different moisture conditions (30% and 50% WFPS). Based on detection limits for NO, NO2, N2O, and CH4 fluxes of < 0.5 µg N or C m−2 h−1 and for CO2 fluxes of < 1.2 mg C m−2 h−1, we found that soil CO2, CH4, NO, NO2, and N2O were significantly affected by different soil moisture levels. After 17 days cumulative fluxes at 50% WFPS increased by 40, 400, and 500% for CO2, N2O, and CH4, respectively, when compared to 30% WFPS. However, cumulative fluxes for NO, and NO2, decreased by 70, and 40%, respectively, at 50% WFPS when compared to 30% WFPS. Different NO concentrations tended to decrease soil C and N fluxes by about 10–20%. However, with the observed variability among individual soil mesocosms and minor fluxes change. In conclusion, the developed system effectively investigates how and to what extent soil NO concentrations affect soil processes and potential plant–microbe interactions in the rhizosphere. [ABSTRACT FROM AUTHOR]

The recovery of energy potential through anaerobic digestion is a widely used method for treating biodegradable waste. However, challenges related to operational issues, waste characterization, and process instability hinder its widespread application and result in low methane yields. This review aims to organize and analyze the static and dynamic parameters that influence biogas yield in order to optimize its production. Biogas typically consists of 50–70% methane (CH4) and 30–50% carbon dioxide (CO2) along with traces of other gases. The paper highlights various solutions to enhance CH4 production, including substrate pre-treatment, co-digestion, Fe0 powder addition, anaerobic fungi, multi-stage biodigester design, and controlling factors influencing anaerobic digestion. These factors primarily include methanogenic potential, C/N ratio, digestion temperature, pH, reactor tightness, and Pressure. However, the use of bioreactors faces technical, socio-economic, and environmental constraints that vary between developed and less developed countries, as discussed in the paper. Through an analysis of over 30 substrate types, the optimum ratios for certain substrates to achieve higher biogas yields were identified. For cow manure mixed with other materials, the yield increases within a C/N ratio of 20–30 and decreases at a ratio of 35. In the case of poultry droppings mixed with other substrates, the yield increases within a C/N ratio of 18–22. Food waste yield, on the other hand, varies significantly due to the differing characteristics of food waste sources. In summary, this study emphasizes the importance of optimizing biogas production through understanding and controlling the influencing factors. It provides insights into potential solutions and optimum substrate ratios for improved biogas yield. [ABSTRACT FROM AUTHOR]

We describe a novel biosafety aerosol chamber equipped with state-of-theart instrumentation for bubble-bursting aerosol generation, size distribution measurement, and condensation-growth collection to minimize sampling artifacts when measuring virus infectivity in aerosol particles. Using this facility, we investigated the effect of relative humidity (RH) in very clean air without trace gases (except ~400 ppm CO2) on the preservation of influenza A virus (IAV) infectivity in saline aerosol particles. We characterized infectivity in terms of 99%-inactivation time, t99, a metric we consider most relevant to airborne virus transmission. The viruses remained infectious for a long time, namely t99 > 5 h, if RH < 30% and the particles effloresced. Under intermediate conditions of humidity (40% < RH < 70%), the loss of infectivity was the most rapid (t99 ∾ 15-20 min, and up to t99 ∾ 35 min at 95% RH). This is more than an order of magnitude faster than suggested by many previous studies of aerosol-borne IAV, possibly due to the use of matrices containing organic molecules, such as proteins, with protective effects for the virus. We tested this hypothesis by adding sucrose to our aerosolization medium and, indeed, observed protection of IAV at intermediate RH (55%). Interestingly, the t99 of our measurements are also systematically lower than those in 1-mL droplet measurements of organic-free saline solutions, which cannot be explained by particle size effects alone. [ABSTRACT FROM AUTHOR]

Atmospheric methane oxidizing bacteria (atmMOB) constitute the sole biological sink for atmospheric methane. Still, the physiological basis allowing atmMOB to grow on air is not well understood. Here we assess the ability and strategies of seven methanotrophic species to grow with air as sole energy, carbon, and nitrogen source. Four species, including three outside the canonical atmMOB group USCα, enduringly oxidized atmospheric methane, carbon monoxide, and hydrogen during 12 months of growth on air. These four species exhibited distinct substrate preferences implying the existence of multiple metabolic strategies to grow on air. The estimated energy yields of the atmMOB were substantially lower than previously assumed necessary for cellular maintenance in atmMOB and other aerobic microorganisms. Moreover, the atmMOB also covered their nitrogen requirements from air. During growth on air, the atmMOB decreased investments in biosynthesis while increasing investments in trace gas oxidation. Furthermore, we confirm that a high apparent specific affinity for methane is a key characteristic of atmMOB. Our work shows that atmMOB grow on the trace concentrations of methane, carbon monoxide, and hydrogen present in air and outlines the metabolic strategies that enable atmMOB to mitigate greenhouse gases. Atmospheric methane-oxidizing bacteria constitute the sole biological sink for atmospheric methane. Here, Schmider et al. assess the ability and strategies of seven methanotrophic species to grow with air as sole energy, carbon, and nitrogen source, showing that these bacteria can grow on the trace concentrations of methane, carbon monoxide, and hydrogen present in air. [ABSTRACT FROM AUTHOR]

The Pyrenean Platform for Observation of the Atmosphere (P2OA) is a coupled plain–mountain instrumented platform in southwestern France. It is composed of two physical sites: the "Pic du Midi" mountaintop observatory (2877 m a.s.l.) and the "Centre de Recherches Atmosphériques" (600 m a.s.l). Both sites are complementarily instrumented for the monitoring of climate-relevant variables and the study of meteorological processes in a mountainous region. The scientific topics covered by P2OA include surface–atmosphere interactions in heterogeneous landscapes and complex terrain, the physics and chemistry of atmospheric trace species at a large scale, the influence of local- and regional-scale emissions and transport on the atmospheric composition, and transient luminous events above thunderstorms. With a large number of instruments and a high hosting capacity, P2OA contributes to atmospheric sciences through (i) building long-term series of atmospheric observations, (ii) hosting experimental field campaigns and instrumental tests, and (iii) educational training in atmospheric observation techniques. In this context, P2OA is part of the French component of the Aerosol, Clouds and Trace Gases Research Infrastructure (ACTRIS-Fr) and also contributes to the Integrated Carbon Observation System (ICOS) research infrastructure and to several European or international networks. Here, we present the complete instrumentation of P2OA and the associated datasets, give a meteorological characterization of the platform, and illustrate the potential of P2OA and its dataset with past or ongoing studies and projects. [ABSTRACT FROM AUTHOR]

Chlorine species play a crucial role as precursors to Cl radicals, which can significantly impact the atmospheric oxidation capacity and influence the levels of trace gases related to climate and air quality. Several studies have established a chlorine emission inventory in China in recent years, but the emission remains uncertain and requires further investigation. The Anthropogenic Chlorine Emission Inventory for China (ACEIC) was the first chlorine emission inventory for China based on local data developed in our previous study, which only includes the emissions from coal combustion and waste incineration. In this study, we updated this inventory to include data for a more recent year (2019) and expanded the range of species considered (HCl, fine particulate Cl - , Cl 2 , and hypochlorous acid (HOCl)) and the number of anthropogenic sources (41 specific sources). Compared with previous studies, this updated inventory considered more anthropogenic sources, used more localized emission factors, and adopted more refined estimation methods. The total emissions of HCl, fine particulate Cl - , Cl 2 , and HOCl in mainland China for the year 2019 were estimated to be 361 (- 18 % to 27 %), 174 (- 27 % to 59 %), 18 (- 10 % to 15 %), and 79 (- 12 % to 18 %) Gg, respectively. To facilitate analysis, we aggregated the chlorine emissions from various sources into five economic sectors: power, industry, residential, agriculture, and biomass burning. HCl emissions were primarily derived from the industry (43 %), biomass burning (38 %), and residential (13 %) sectors. The biomass burning and industry sectors accounted for 74 % and 19 % of the fine particulate Cl - emissions, respectively. Residential and industry sectors contributed 61 % and 29 % of the total Cl 2 emissions. HOCl emissions were predominantly from the residential sector, constituting 90 % of the total emissions. Notably, the usage of chlorine-containing disinfectants was identified as the most significant source of Cl 2 and HOCl emissions in the residential sector. Geographically, regions with high HCl and fine particulate Cl - emissions were found in the North China Plain, northeastern China, central China, and the Yangtze River Delta, whereas the Pearl River Delta, Yangtze River Delta, and Beijing–Tianjin–Hebei regions exhibited elevated levels of Cl 2 and HOCl emissions. Regarding monthly variation, emissions of HCl and fine particulate Cl - were higher during early spring (February to April) and winter (December to January) due to intensified agricultural activities, while Cl 2 and HOCl emissions were higher in the summer months due to increased demand for water disinfection. We incorporated this emission inventory into the chemical transport model and found the simulated concentrations of chlorine species agreed reasonably well with the observations, which suggested the relatively faithful estimations of their emissions. This updated inventory contributes to a better understanding of anthropogenic sources of chlorine species and can aid in the formulation of emission control strategies to mitigate secondary pollution in China. [ABSTRACT FROM AUTHOR]

To accurately assess the current atmospheric methane budget and its future trends, it is essential to apportion and quantify the anthropogenic methane emissions to specific sources. This poses a significant challenge in the under‐sampled Middle East, where estimates predominantly depend on remote sensing observations and bottom‐up reporting of national emissions. Here, we present in situ shipborne observations of greenhouse gases (GHGs) and non‐methane hydrocarbons (NMHCs) collected along a >10,000‐km route from Vigo, Spain, to Abu Dhabi, UAE. By comparing our observations with Lagrangian dispersion model simulations, coupled with two methane emission inventories, we identify periods of considerable mismatch and apportion the responsible sources. Employing interspecies relationships with NMHCs has enabled the characterization of methane emissions from oil and gas (O&G) operations, urban centers, Red Sea deep water, enteric fermentation, and agriculture across diverse atmospheric environments. Our analysis reveals that the Suez area is a regional emission hotspot, where simulations consistently underestimate the methane emission sources. Importantly, the Middle Eastern O&G sector has been identified as an additional source of considerable uncertainty. Here, methane emissions were alternately underestimated and overestimated by the two inventories, exposing significant gaps in our understanding of fuel exploitation‐related emissions in the Middle East. This underscores the need for further targeted field campaigns and long‐term observations to improve the accuracy of emission data in the inventories. Plain Language Summary: For the mitigation of human‐induced methane emissions, a detailed characterization of its numerous sources is vital. This is particularly challenging in understudied regions where the source attribution and emission strength thus far relies on satellite observations and country reports. Although such data, representing the entire atmospheric column, are invaluable, source specific emission estimates remain highly uncertain. In this study, we used shipborne measurements of methane to evaluate the performance of two emission inventories commonly used in computer‐based models to simulate methane atmospheric concentrations. The relationships between methane and various co‐emitted reactive trace gases revealed the causes of discrepancies between observations and model simulations. Our results show that, while models are generally reliable at capturing high methane concentrations, they are deficient in the Suez and Middle East areas due to inadequate characterization of emissions from Oil and Gas operations. The research outcomes of this study underscore the crucial role of ground‐based observations in improving the accuracy of methane emission inventories and their reporting, and in supporting evidence‐based policies to mitigate climate change and improve air quality. Key Points: The Suez Canal and the Gulf of Suez are regional pollution hotspots with underestimated methane emission sourcesDiscrepancies between observed and modeled methane mixing ratios were resolved using non‐methane hydrocarbon observationsMethane sources from the oil and gas exploitation sector in the Middle East are particularly uncertain in emission inventories [ABSTRACT FROM AUTHOR]

Acetonitrile plays an important role in atmospheric processes and serves as a key tracer of biomass burning, the major emission source of primary carbonaceous particles and trace gases in the global atmosphere. Recognizing its significance, the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) has designated acetonitrile as one of the target volatile organic compounds for global atmospheric monitoring, aiming for data quality better than 20 % accuracy and 15 % precision. Meeting the objectives of the WMO GAW program requires accurate and stable calibration standards with uncertainties of less than 5 %. In this study, we explored the feasibility of gravimetry for developing primary standard gas mixtures (PSMs) in three different types of aluminium cylinders, each with distinct internal surface treatments, at nmol mol-1 and µmol mol-1 levels with a relative expanded uncertainty of less than 5 %. We found that all three types of cylinders were inadequate, without further passivation, for developing acetonitrile PSMs below 10 nmol mol-1 due to significant adsorption losses (6 %–49 %) onto the cylinder's inner surface. To overcome this challenge, we prepared acetonitrile gas mixtures at 100 nmol mol-1 using a modified gravimetric method and at 10 µmol mol-1 using a conventional gravimetric method and then evaluated their long-term stability. Results showed that the effect of the adsorption loss at 100 nmol mol-1 and 10 µmol mol-1 was negated and negligible, respectively. Stability results show that we can disseminate acetonitrile calibration standards at both 100 nmol mol-1 and 10 µmol mol-1 with a relative expanded uncertainty of 3 % and 1 %, respectively (with an expiration period of 3 years), meeting the target uncertainty of the WMO GAW program. Further research is still needed to develop accurate and stable acetonitrile calibration standards below 10 nmol mol-1 that are closer to atmospheric levels. [ABSTRACT FROM AUTHOR]

The atmosphere of Mars has been studied for many years now by a long series of missions. The paper focuses on the results obtained by two of these that are led by European researchers overseen by the European Space Agency, i.e., Mars Express which was launched in 2003 and ExoMars Trace Gas Orbiter launched in 2016. Both missions are still providing high-quality data about the atmosphere of Mars, such as abundances of its key species – CO2, CO, H2O, O3 - playing an important role in the different cycles existing on the planet, as well as other trace gases – O2 (mixing ratio of 3.1 to 5.8 × 10−3 above 90 km), the recently discovered HCl (up to 4 ppbv below 30 km), and the elusive CH4 (stringent detection limit of 20 pptv). Some instruments are also sensitive enough to provide information on isotopologues of the key elements and have delivered for some of these the first and unique vertical profiles available today ( δ 13 C and δ 18 O in CO2 and CO, D/H, δ 17 O and δ 18 O in water vapour). The paper retraces the history of the exploration of the Martian atmosphere putting the results from both missions in perspective. [ABSTRACT FROM AUTHOR]

Trace gas analysis is a key tool for the investigation of man-made environmental pollution as well as for early detection of respiratory diseases. To detect tiny concentrations, sensitive methods such as cavity ring down spectroscopy or plasmonic sensors have been used. Here, we demonstrate the combination of the photoacoustic effect in a classical cell with a novel, rapidly tunable, narrowband fiber-feedback optical parametric oscillator. The high sensitivity of photoacoustic cells and the extremely narrow linewidth as well as the wide and rapid tunability of the fiber-feedback optical parametric oscillator enable a high resolution of the rotational and vibrational bands of molecules in the near-infrared region. Photoacoustic spectra of methane, carbon dioxide, and water at ambient pressure are obtained in a broad spectral range and compared to high-resolution transmission molecular absorption database. In particular, scanning the entire carbon dioxide overtone around 4965 cm−1 at 2000 ppm takes 185 s with a signal-to-noise ratio of 31. This approach enables a wide tunability in the entire near- and mid-infrared spectral region suitable for many environmental and medical applications. [ABSTRACT FROM AUTHOR]

Many chemical transport models treat mineral dust as spherical. Solar backscatter retrievals of trace gases (e.g., OMI and TROPOMI) implicitly treat mineral dust as spherical. The impact of the morphology of mineral dust particles is studied to assess its implications for global chemical transport model (GEOS‐Chem) simulations and solar backscatter trace gas retrievals at ultraviolet and visible (UV‐Vis) wavelengths. We investigate how the morphology of mineral dust particles affects the simulated dust aerosol optical depth; surface area, reaction, and diffusion parameters for heterogeneous chemistry; phase function, and scattering weights for air mass factor (AMF) calculations used in solar backscatter retrievals. We use a mixture of various aspect ratios of spheroids to model the dust optical properties and a combination of shape and porosity to model the surface area, reaction, and diffusion parameters. We find that assuming spherical particles can introduce size‐dependent and wavelength‐dependent errors of up to 14% in simulated dust extinction efficiency with corresponding error in simulated dust optical depth typically within 5%. We find that use of spheroids rather than spheres increases forward scattered radiance and decreases backward scattering that in turn decrease the sensitivity of solar backscatter retrievals of NO2 to aerosols by factors of 2.0–2.5. We develop and apply a theoretical framework based on porosity and surface fractal dimension with corresponding increase in the reactive uptake coefficient driven by increased surface area and species reactivity. Differences are large enough to warrant consideration of dust non‐sphericity for chemical transport models and UV‐Vis trace gas retrievals. Plain Language Summary: Mineral dust is often treated as spherical in chemical transport and trace gas retrieval models. In this study, we investigate how dust shape affects gas‐particle and radiation‐particle interactions. We examine the impact of dust shape on optical properties and trace gas retrievals at ultraviolet and visible wavelengths. We find that treating dust as nonspherical in trace gas retrievals of nitrogen dioxide decreases the retrieval sensitivity to dust. We also examine the impact of dust shape on heterogeneous chemistry by developing and applying a theoretical model. We find that dust pores change particle surface area significantly and subsequently, reaction and diffusion parameters. Overall, this study signifies the importance of accounting for nonsphericity in chemical transport and trace gas retrieval models. Key Points: We implement a spheroidal model for dust shape along with the porosity to examine dust morphology effects in a chemical transport modelNonspherical dust particles with pores increase surface area available for reactive uptakeSpheroidal rather than spherical dust treatment reduces the effects of aerosols on UV‐Vis NO2 retrievals by factors of 2.0–2.5 [ABSTRACT FROM AUTHOR]

A gas analyzer has been developed using cavity ring‐down spectroscopy (CRDS) technology, designed to simultaneously measure the concentrations of CO2 and CO. These gases are critical indicators of transformer insulation degradation. The analyzer covers a CO2 concentration range from a few ppm to several thousand ppm and can measure CO/CO2 concentration ratios from 0.076 to 0.8. The selected absorption lines for CO and CO2 are centered at 6337.99 and 6338.59 cm−1, respectively. The two candidate lines are proximate to each other and nonoverlapping. The experimental results indicate that the system accurately fits the measured and calculated signals, enabling concentration measurements at the ppm level. This confirms its ability to measure the gas concentrations and ratios critical for assessing the condition of transformer insulation. This CRDS‐based system offers a reliable and sensitive method for early detection of potential transformer faults. [ABSTRACT FROM AUTHOR]

The relationships among sea ice melting, phytoplankton assemblages, and the production of climate‐relevant trace gases in the Southern Ocean are gaining increasing attention from the scientific community. This is particularly true for dimethyl sulfide (DMS), which plays an important role in atmospheric chemistry by influencing the formation of sulfated aerosols with radiative impacts and constituting cloud condensation nuclei. In the current study, chlorophyll a (Chl a), DMS and its precursors dimethylsulfoniopropionate (DMSP), were quantified in the Weddell–Scotia Confluence (WSC) during the 2018 record ice extent minimum period. Mixed layer changes were found to be generally associated with spatial variation in sea ice melt, with the depth being six times deeper in ice‐free, well‐mixed regions than in seasonal ice‐melting zones. The surface Chl a concentration increased from ice‐free to ice‐melting regions with elevated sea ice meltwater percentages and drawdown surface nutrient concentrations. The concentrations of surface and depth‐integrated Chl a in the upper 150 m reached maxima in the ice‐melting region with the highest fraction of sea ice meltwater, illustrating that sea ice melting promoted the occurrence of phytoplankton blooms. The DMS and DMSP concentrations in the vicinity of the ice‐melting zone were approximately three times higher than those in the ice‐free waters. The observations of this study show that the regions of ice melting in the WSC were a zone of particularly high sea–air fluxes of DMS, which could significantly contribute to the atmospheric budget of DMS in the polar regions. [ABSTRACT FROM AUTHOR]

Monitoring, reporting, and verification frameworks for greenhouse gas emissions are being developed by countries across the world to keep track of progress towards national emission reduction targets. Data assimilation plays an important role in monitoring frameworks, combining different sources of information to achieve the best possible estimate of fossil fuel emissions and, as a consequence, better estimates for fluxes from the natural biosphere. Robust estimates for fossil fuel emissions rely on accurate estimates of uncertainties corresponding to different pieces of information. We describe prior uncertainties in CO 2 and CO fossil fuel fluxes, paying special attention to spatial error correlations and the covariance structure between CO 2 and CO. This represents the first time that prior uncertainties in CO 2 and the important co-emitted trace gas CO are defined consistently, with error correlations included, which allows us to make use of the synergy between the two trace gases to better constrain CO 2 fossil fuel fluxes. CO:CO2 error correlations differ by sector, depending on the diversity of sub-processes occurring within a sector, and also show a large range of values between pixels within the same sector. For example, for other stationary combustion, pixel correlation values range from 0.1 to 1.0, whereas for road transport, the correlation is mostly larger than 0.6. We illustrate the added value of our definition of prior uncertainties using closed-loop numerical experiments over mainland Europe and the UK, which isolate the influence of using error correlations between CO 2 and CO and the influence of prescribing more detailed information about prior emission uncertainties. For the experiments, synthetic in situ observations are used, allowing us to validate the results against a "truth". The "true" emissions are made by perturbing the prior emissions (from an emission inventory) according to the prescribed prior uncertainties. We find that using our realistic definition of prior uncertainties helps our data assimilation system to differentiate more easily between CO 2 fluxes from biogenic and fossil fuel sources. Using improved prior emission uncertainties, we find fewer geographic regions with significant deviations from the prior compared to when using default prior uncertainties (32 vs. 80 grid cells of 0.25°×0.3125° , with an absolute difference of more than 1 kg s -1 between the prior and posterior), but these deviations from the prior almost consistently move closer to the prescribed true values, with 92 % showing an improvement, in contrast to the default prior uncertainties, where 61 % show an improvement. We also find that using CO provides additional information on CO 2 fossil fuel fluxes, but this is only the case if the CO:CO2 error covariance structure is defined realistically. Using the default prior uncertainties, the CO 2 fossil fuel fluxes move farther away from the truth in many geographical regions (with 50 % showing an improvement compared to 94 % when advanced prior uncertainties are used). With the default uncertainties, the maximum deviation of fossil fuel CO 2 from the prescribed truth is about 7 % in both the prior and posterior results. With the advanced uncertainties, this is reduced to 3 % in the posterior results. [ABSTRACT FROM AUTHOR]

In the past, satellite climatologies of gravity waves (GWs) have initiated progress in their representation in global models. However, these could not provide the phase speed and direction distributions needed for a better understanding of the interaction between GWs and the large-scale winds directly. The ESA Earth Explorer 11 candidate CAIRT could provide such observations. CAIRT would use a limb-imaging Michelson interferometer resolving a wide spectral range, allowing temperature and trace gas mixing ratio measurements. With the proposed instrument design, a vertical resolution of 1 km, along-track sampling of 50 km, and across-track sampling of 25 km in a 400 km wide swath will be achieved. In particular, this allows for the observation of three-dimensional (3D), GW-resolving temperature fields throughout the middle atmosphere. In this work, we present the methodology for the GW analysis of CAIRT observations using a limited-volume 3D sinusoidal fit (S3D) wave analysis technique. We assess the capability of CAIRT to provide high-quality GW fields by the generation of synthetic satellite observations from high-resolution model data and comparison of the synthetic observations to the original model fields. For the assessment, wavelength spectra, phase speed spectra, horizontal distributions, and zonal means of GW momentum flux (GWMF) are considered. The atmospheric events we use to exemplify the capabilities of CAIRT are the 2006 sudden stratospheric warming (SSW) event, the quasi-biennial oscillation (QBO) in the tropics, and the mesospheric preconditioning phase of the 2019 SSW event. Our findings indicate that CAIRT would provide highly reliable observations not only of global-scale GW distributions and drag patterns but also of specific wave events and their associated wave parameters. Even under worse-than-expected noise levels of the instrument, the resulting GW measurements are highly consistent with the original model data. Furthermore, we demonstrate that the estimated GW parameters can be used for ray tracing, which physically extends the horizontal coverage of the observations beyond the orbit tracks. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate the utility of available correlative measurements of carbon species to identify regional and local air mass characteristics as well as their associated source types. In particular, we combine different regression techniques and enhancement ratio algorithms with carbon monoxide (CO), carbon dioxide (CO 2), and methane (CH 4) total column abundance from 11 sites of the Total Carbon Column Observing Network (TCCON) to infer relative contributions of regional and local sources to each of these sites. The enhancement ratios provide a viable alternative to univariate measures of relationships between the trace gases that are insufficient in capturing source-type and transport signatures. Regional enhancements are estimated from the difference between bivariate regressions across a specific time window of observed total abundance of these species (BERr for bulk enhancement regression ratio) and inferred anomalies (AERr for anomaly enhancement regression ratio) associated with a site-specific background. Since BERr and AERr represent the bulk and local species enhancement ratio, respectively, its difference simply represents the site-specific regional component of these ratios. We can then compare these enhancements for CO 2 and CH 4 with CO to differentiate between combustion and non-combustion air masses. Our results show that while the regional and local influences in enhancements vary across sites, dominant characteristics are found to be consistent with previous studies over these sites and with bottom-up anthropogenic and fire emission inventories. The site in Pasadena shows a dominant local influence (> 60 %) across all species enhancement ratios, which appear to come from a mixture of biospheric and combustion activities. In contrast, Anmyeondo shows more regionally influenced (> 60 %) air masses associated with high-temperature and/or biofuel combustion activities. Ascension Island appears to only show a large regional influence (> 80 %) on CO / CO 2 and CO / CH 4 , which is indicative of transported and combustion-related CO from the nearby African region, consistent with a sharp rise in column CO (3.51 ± 0.43 % ppb yr -1) at this site. These methods have important applications to source analysis using spaceborne column retrievals of these species. [ABSTRACT FROM AUTHOR]

The Environmental Trace Gases Monitoring Instrument (EMI) series are second-generation Chinese spectrometers on board the GaoFen-5 (GF-5) and DaQi-1 (DQ-1) satellites. In this study, a comparative analysis of EMI series data was conducted to determine the daily trend of ozone concentration changes owing to different transit times and to improve the overall quality and reliability of EMI series datasets. The daily EMI total ozone column (TOC) obtained using the Differential Optical Absorption Spectroscopy (DOAS) method were compared to vertical column density (VCD) gathered by the TROPOspheric Monitoring Instrument (TROPOMI). The results from October to November 2023 indicated a fine correlation (R = 0.98) between the daily EMI series data and a fine correlation (R ≥ 0.95) and spatial distribution closely resembling that of the TROPOMI TOCs. Furthermore, the EMI series data fusion results were highly correlated with TROPOMI TOCs (R = 0.99). Since the EMI series instruments had two different overpass times and the volume of available data at same pixel was increased by approximately three-fold, the temporal and spatial resolution was improved a lot. The results indicated that, compared to a single sensor, the EMI series DOAS TOCs generated more accurate and stable global TOC results and also enabled looking at the changes in the intraday TOCs. These outcomes highlight the potential of the EMI instruments for reliably monitoring the ozone variations in polar regions. [ABSTRACT FROM AUTHOR]

Studies of the impact of biomass burning and the emissions of trace gases from biomass burning, especially using long-term observations, are scarce in China. We utilize solar absorption spectra obtained via ground-based high-resolution Fourier transform infrared (FTIR) spectroscopy to retrieve the atmospheric total columns and vertical profiles of carbon monoxide (CO), formaldehyde (H2CO), and hydrogen cyanide (HCN) in Hefei, China. Seasonal and interannual variability in the three gases from 2016 to 2022 are analyzed. Atmospheric CO shows significant seasonal variations, peaking during spring and winter, and declining during summer, with a seasonal amplitude of 8.07 × 1017 molecules cm−2 and a seasonal variability of 29.35%. H2CO and HCN have similar seasonal patterns to each other, with high concentrations in summer and low concentrations in winter. The seasonal amplitude of H2CO and HCN are 1.89 × 1016 molecules cm−2 and 2.32 × 1015 molecules cm−2, respectively, with a seasonal variability of 133.07% and 34.69%, respectively. The means of the annual variation rate for CO, H2CO, and HCN are (−2.67 ± 2.88)% yr−1, (2.52 ± 12.48)% yr−1 and (−3.48 ± 7.26)% yr−1, respectively. To assess the influence of biomass burning on the variations in column concentrations of the three gases, the correlation between CO, H2CO, and HCN was analyzed. The months during which the monthly correlation coefficient between CO and H2CO with HCN exceeds 0.8, and the fire radiative power (FRP) observed by satellites is larger than its monthly average are regarded as a biomass-burning occurrence in Anhui province. Additionally, the enhancement ratios of ΔH2CO/ΔCO and ΔHCN/ΔCO were calculated for the periods impacted by the biomass burning. Finally, backward trajectory cluster analysis and the potential source contribution function (PSCF) calculation identified the air mass transport pathways and the potential source areas at the Hefei site. [ABSTRACT FROM AUTHOR]

Biogenic volatile organic compounds (VOCs) constitute a significant portion of gas-phase metabolites in modern ecosystems and have unique roles in moderating atmospheric oxidative capacity, solar radiation balance, and aerosol formation. It has been theorized that VOCs may account for observed geological and evolutionary phenomena during the Archaean, but the direct contribution of biology to early non-methane VOC cycling remains unexplored. Here, we provide an assessment of all potential VOCs metabolized by the last universal common ancestor (LUCA). We identify enzyme functions linked to LUCA orthologous protein groups across eight literature sources and estimate the volatility of all associated substrates to identify ancient volatile metabolites. We hone in on volatile metabolites with confirmed modern emissions that exist in conserved metabolic pathways and produce a curated list of the most likely LUCA VOCs. We introduce volatile organic metabolites associated with early life and discuss their potential influence on early carbon cycling and atmospheric chemistry. [ABSTRACT FROM AUTHOR]

This study concerns the development of a maghemite (γ-Fe2O3)-coupled tetra sulfophenyl porphyrin (TSPP) thin film–based optical waveguide (OWG) sensor (TSPP-γ-Fe2O3-OWG) for the detection of ethylenediamine (EDA). For ease of manufacture, we fabricated sensors using a spin-coating technique, and characterized their response based on their ultraviolet-visible (UV-vis) absorption spectra and the response intensity of OWG sensor. We have observed significant changes in the location of the peaks in the sensor's UV-vis absorption spectra after exposed to EDA gas, indicating aggregation of TSPP. Optical characterization confirmed that the combination of TSPP with maghemite (TSPP-γ-Fe2O3-OWG) had improved device response, with twice as high as those of the acid-treated TSPP-OWG sensor, and 30 times higher than that of the pure γ-Fe2O3-OWG sensor. At ambient temperature, the composite sensor exhibited a linear response to EDA gas in the concentration range of 0.1–1000 ppm with signal-to-noise ratio (S/N) 8.33, confirming that the improved stability of the composite TSPP-γ-Fe2O3 thin-film OWG enables the detection of trace amounts of gas with high sensitivity and selectivity. [ABSTRACT FROM AUTHOR]

Globally, the emission of biogenic volatile organic compounds (BVOC) by plants represents the dominant source of volatile organic compounds emitted to the atmosphere. Monoterpenes, as the major BVOC group, can contribute to forming secondary organic aerosols and influence cloud properties. In this study, we developed a process‐based monoterpene module in the Vegetation Integrative SImulator for Trace gases (VISIT) model by considering the production, storage, and emission of monoterpene as three main processes. We further evaluated the modeled monoterpene emissions against the ecosystem‐level observation data at a half‐hour scale at a Japanese larch (Larix kaempferi) forest site on Mt. Fuji, Japan. The VISIT model performed with relatively higher accuracy with a Willmott's index of agreement at 0.61, a mean bias error (MBE) at 0.29, and a root mean squared error (RMSE) at 0.43, comparable to that of Model of Emissions of Gases and Aerosols from Nature model with a Willmott's index of agreement at 0.63, a MBE at 0.40, and a RMSE at 0.54. In a long‐term simulation under high CO2 emission scenarios, the ratio between monoterpene emission and gross primary production exhibited a stronger correlation with CO2 concentration than temperature. Our study provides a process‐based modeling approach for more accurately simulating monoterpene emissions from Japanese larch. Plain Language Summary: This study focuses on constructing the process and improving the accuracy of simulating emissions of biogenic volatile organic compounds (BVOC), specifically monoterpenes, from a Japanese larch forest using the Vegetation Integrative SImulator for Trace gases model. By incorporating a process‐based monoterpene module, the model demonstrated better performance compared to the widely‐used Model of Emissions of Gases and Aerosols from Nature model. The simulated results showed temperature acting as the dominant factor in determining the proportion between gross primary production and monoterpene emission in the short term. In future projections, the analysis emphasized the significant role of long‐term increases in CO2 concentration in determining this proportion. This study provides a valuable tool for simulating site‐based BVOC emissions, contributing to our understanding of the complex interactions between vegetation and the atmosphere. Key Points: The process‐based ecosystem model shows better performance than empirical model in modeling monoterpene emission from a Japanese larchHigh emission of CO2 in future will significantly influence the proportion between gross primary production and monoterpene emission [ABSTRACT FROM AUTHOR]

Land surface changes can have substantial impacts on biosphere–atmosphere interactions. In South America, rainforests abundantly emit biogenic volatile organic compounds (BVOCs), which, when coupled with pyrogenic emissions from deforestation fires, can have substantial impacts on regional air quality. We use novel and long-term satellite records of five trace gases, namely isoprene (C 5 H 8), formaldehyde (HCHO), methanol (CH 3 OH), carbon monoxide (CO), and nitrogen dioxide (NO 2), in addition to aerosol optical depth (AOD), vegetation (land cover and leaf area index), and burned area. We characterise the impacts of biogenic and pyrogenic emissions on atmospheric composition for the period 2001 to 2019 in the southern Amazon, a region of substantial deforestation. The seasonal cycle for all of the atmospheric constituents peaks in the dry season (August–October), and the year-to-year variability in CO, HCHO, NO 2 , and AOD is strongly linked to the burned area. We find a robust relationship between the broadleaf forest cover and total column C 5 H 8 (R2 = 0.59), while the burned area exhibits an approximate fifth root power law relationship with tropospheric column NO 2 (R2 = 0.32) in the dry season. Vegetation and burned area together show a relationship with HCHO (R2 = 0.23). Wet-season AOD and CO follow the forest cover distribution. The land surface variables are very weakly correlated with CH 3 OH, suggesting that other factors drive its spatial distribution. Overall, we provide a detailed observational quantification of biospheric process influences on southern Amazon regional atmospheric composition, which in future studies can be used to help constrain the underpinning processes in Earth system models. [ABSTRACT FROM AUTHOR]

We present a novel dataset that extends our view of the cosmic gas around z ≈ 3 − 4 Lyα emitters (LAEs) in the Muse Analysis of Gas around Galaxies (MAGG) survey by tracing a cool and enriched gas phase through 47 Mg II absorbers identified in newly obtained VLT/X-shooter near-infrared quasar spectra. Jointly with the more ionized gas traced by C IV systems and the neutral H I from previous work, we find that LAEs are distributed inside cosmic structures that contain multiphase gas in composition and temperature. All gas phases are a strong function of the large-scale galaxy environment: the Mg II and the C IV strength and kinematics positively correlate with the number of associated galaxies, and it is ≈3 − 4 times more likely to detect metal absorbers around groups of LAEs than isolated ones. Exploring the redshift evolution, the covering factor of Mg II around groups of LAEs and isolated ones remains approximately constant from z ≈ 3 − 4 to z ≲ 2, but the one of C IV around group galaxies drops by z ≲ 2. Adding the cool enriched gas traced by the Mg II absorbers to the results that we obtained for the H I and C IV gas, we put forward a picture in which LAEs lie along gas filaments that contain high column-density H I systems and are enriched by strong C IV and Mg II absorbers. While the Mg II gas appears to be more centrally concentrated near LAEs, weaker C IV systems instead trace a more diffuse gas phase extended up to larger distances around the galaxies. [ABSTRACT FROM AUTHOR]

Concern over increasing pollution and ways to mitigate it is in high demand due to the swift advancement of technology and the creation of advanced utilities. Nitrogen oxide (NO2) is a well‐known evolved toxin that poses a threat to human health, the environment, and biodiversity. Therefore, several works are carried to sense the NO2 gas at its trace concentration. However, the majority of NO2 sensors that have been reported have inadequate Limit of Detection (LOD), high operating temperature, and low sensitivity. Orthorhombic molybdenum oxide (α‐MoO3) recently emerged as hotspot in the gas sensing research and noted for its high sensitivity, and distinct sensing capabilities owing to its unique layered structure. In this study, Fe‐doped α‐MoO3 nanosheets for NO2 sensing is prepared, and at a low operating temperature of 110 °C, an excellent sensitivity of 1282% for 10 ppm of NO2 is achieved. Long‐term stability, good repeatability, and an ultra‐low detection limit of 79 ppt are also demonstrated by the manufactured sensors. In addition, the obtained low activation energy of ‐2.9 KJ mol−1 and the high band bending for FM6 supports the highly responsive NO2 detection at low operating temperatures. [ABSTRACT FROM AUTHOR]

Quantification of wildfire emissions is essential for comprehending and simulating the effects of wildfires on atmospheric chemical composition. Sub-orbital measurements of vertical column nitrous acid (HONO) and nitrogen dioxide (NO2) were made during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field campaign using the GeoCAPE Airborne Simulator (GCAS) instrument aboard the NASA ER-2 aircraft. Emission rates and lifetimes of HONO and NO2 from the Sheridan Fire were estimated by fitting exponentially modified Gaussians (EMGs) to line densities, a technique previously used to estimate urban and point source NO2 emissions. As the EMG approach does not capture temporal changes in emissions and lifetimes due to time-varying fire behavior, we developed a Monte Carlo implementation of the Python Editable Chemical Atmospheric Numeric Solver (PECANS) model that includes diurnal fire radiative power (FRP) behavior. We assess the validity of a range of emission rate and lifetime combinations for both HONO and NO2 as the fire evolves by comparing the resulting line density predictions to the observations. We find that our method results in emissions that are lower than top-down biomass burning emissions inventories and higher than bottom-up inventories. Our approach is applicable to interpreting time-resolved remotely sensed measurements of atmospheric trace gases such as those now becoming available with instruments aboard geo-stationary satellites such as the Tropospheric Emissions: Monitoring of Pollution (TEMPO) and the Geostationary Environment Monitoring Spectrometer (GEMS) instruments. [ABSTRACT FROM AUTHOR]

The Total Carbon Column Observing Network (TCCON) and the Infrared Working Group of the Network for the Detection of Atmospheric Composition Change (NDACC-IRWG) are two ground-based networks that provide the retrieved concentrations of up to 30 atmospheric trace gases, using solar absorption spectrometry. Both networks provide reference measurements for the validation of satellites and models. TCCON concentrates on long-lived greenhouse gases (GHGs) for carbon cycle studies and validation. The number of sites is limited, and the geographical coverage is uneven, covering mainly Europe and the USA. A better distribution of stations is desired to improve the representativeness of the data for various atmospheric conditions and surface conditions and to cover a large latitudinal distribution. The two successive Fiducial Reference Measurements for Greenhouse Gases European Space Agency projects (FRM4GHG and FRM4GHG2) aim at the assessment of several low-cost portable instruments for precise measurements of GHGs to complement the existing ground-based sites. Several types of low spectral resolution Fourier transform infrared (FTIR) spectrometers manufactured by Bruker, namely an EM27/SUN, a Vertex70, a fiber-coupled IRCube, and a Laser Heterodyne spectro-Radiometer (LHR) developed by UK Rutherford Appleton Laboratory are the participating instruments to achieve the Fiducial Reference Measurements (FRMs) status. Intensive side-by-side measurements were performed using all four instruments next to the Bruker IFS 125HR high spectral resolution FTIR, performing measurements in the NIR (TCCON configuration) and MIR (NDACC configuration) spectral range. The remote sensing measurements were complemented by AirCore launches, which provided in situ vertical profiles of target gases traceable to the World Meteorological Organization (WMO) reference scale. The results of the intercomparisons are shown and discussed. Except for the EM27/SUN, all other instruments, including the reference TCCON spectrometer, needed modifications during the campaign period. The EM27/SUN and the Vertex70 provided stable and precise measurements of the target gases during the campaign with quantified small biases. As part of the FRM4GHG project, one EM27/SUN is now used as a travel standard for the verification of column-integrated GHG measurements. The extension of the Vertex70 to the MIR provides the opportunity to retrieve additional concentrations of N2O, CH4, HCHO, and OCS. These MIR data products are comparable to the retrieval results from the high-resolution IFS 125HR spectrometer as operated by the NDACC. Our studies show the potential for such types of spectrometers to be used as a travel standard for the MIR species. An enclosure system with a compact solar tracker and meteorological station has been developed to house the low spectral resolution portable FTIR systems for performing solar absorption measurements. This helps the spectrometers to be mobile and enables autonomous operation, which will help to complement the TCCON and NDACC networks by extending the observational capabilities at new sites for the observation of GHGs and additional air quality gases. The development of the retrieval software allows comparable processing of the Vertex70 type of spectra as the EM27/SUN ones, therefore bringing them under the umbrella of the COllaborative Carbon Column Observing Network (COCCON). A self-assessment following the CEOS-FRM Maturity Matrix shows that the COCCON is able to provide GHG data products of FRM quality and can be used for either short-term campaigns or long-term measurements to complement the high-resolution FTIR networks. [ABSTRACT FROM AUTHOR]

The tropospheric vertical column concentration (VCDtrop) of NO2, SO2, and HCHO was retrieved, respectively, by employing the geometric method (Geomtry), simplified model method (Model), and look-up table method (Table) with the observation spectra of the multi-axis differential absorption spectroscopy instrument (MAX-DOAS). The correlation and relative differences of the inversion results obtained by these three algorithms, as well as the changes in quantiles, were explored. The comparative analysis reveals that the more concentrated the vertical distribution height of gas components is in the near-surface layer, the better the conformity of the VCDtrop retrieved by different algorithms. However, the increase in relative differences is also related to the diurnal variation of gas components. The influence of aerosols on the inversion of the VCDtrop is greater than the change in the vertical distribution height of the gas component itself. The near-surface concentration and distribution height of gas components are the internal factors that give rise to relative differences in the inversion of the VCDtrop by different algorithms, while aerosols are one of the extremely important external reasons. The VCDtrop inverted by Geomtry without considering the influence of aerosols is generally larger except for NO2. Model sets up aerosols in accordance with the height and meteorological conditions of the atmospheric environment. Table can invert the aerosol profile in real time. Compared with Model, it shows a significant improvement in the refined setting of aerosols. Moreover, while obtaining the vertical distribution of aerosols, it can invert the diurnal variation of the VCDtrop. The VCDtrop inverted by Table is the smallest, and the relative difference with Model is on average about 10% smaller. The relative difference of the VCDtrop for the same height (aerosol optical thickness) quantile is 7–15% (about 25% lower on average). When comparing the inversion results of Table with the Ozone Monitoring Instrument (OMI) satellite product, the MAX-DOAS inversion results of NO2, SO2, and HCHO are all larger than the OMI product. This is related to the different observation methods of the MAX-DOAS and OMI and the configuration between the aerosol layer and the distribution height of gas components. [ABSTRACT FROM AUTHOR]

​​​​​​​At the altitudes of the mesosphere–lower thermosphere, OH and HO 2 play a significant role in many physicochemical processes. Thus, monitoring their spatiotemporal evolution, together with other chemically active trace gases, is one of the most important problems for this atmosphere region, in which direct measurements are difficult. This paper studies the nighttime OH and HO 2 chemical equilibria using the 3D chemical transport modeling within the general approach, which includes the identification of the main sources and sinks in the equilibrium space–time areas and the derivation of analytical criteria for equilibrium validity. The presented analysis shows that there are extended areas where nighttime HO 2 and OH are close to their local equilibrium concentrations, determined mainly by the reaction between HOx and Ox components among themselves and with H 2 O 2 , N, NO, NO 2 , and CO. In the upper mesosphere–lower thermosphere, the equilibrium expressions can be shortened so that they include the HOx – Ox chemistry only. These expressions describe the HO 2 and OH equilibria from the top down to some boundaries, the altitude positions of which vary in the interval between 72–73 and 85 km and depend essentially on season and latitude. The developed analytical criteria reproduce the main features of these boundaries well almost everywhere. Due to weak sensitivity to uncertainties of reaction rates and other parameters, the criteria can be regarded as a robust instrument for HO 2 and OH equilibrium validation. The obtained results allow us to extend previously proposed methods for the retrieval of poorly measured components from measurement data and to develop new approaches. [ABSTRACT FROM AUTHOR]

Under the Paris Agreement, countries report their anthropogenic greenhouse gas emissions in national inventories, which are used to track progress towards mitigation goals, but they must be independently verified. Atmospheric observations of CO2 , interpreted using inverse methods, can potentially provide that verification. Conventional CO2 inverse methods infer natural CO2 fluxes by subtracting a priori estimates of fuel combustion from the a posteriori net CO2 fluxes, assuming that a priori knowledge for combustion emissions is better than for natural fluxes. We describe an inverse method that uses measurements of CO2 and carbon monoxide (CO), a trace gas that is co-emitted with CO2 during combustion, to report self-consistent combustion emissions and natural fluxes of CO2. We use an ensemble Kalman filter and the GEOS-Chem atmospheric transport model to explore how satellite observations of CO and CO2 collected by the TROPOspheric Monitoring Instrument (TROPOMI) and Orbiting Carbon Observatory-2 (OCO-2), respectively, can improve understanding of combustion emissions and natural CO2 fluxes across the UK and mainland Europe in 2018–2021. We assess the value of using satellite observations of CO2 , with and without CO, above what is already available from the in situ network. Using CO2 satellite observations leads to small corrections to a priori emissions that are inconsistent with in situ observations, due partly to the insensitivity of the atmospheric CO2 column to CO2 emission changes. When we introduce satellite CO observations, we find better agreement with our in situ inversion and a better model fit to atmospheric CO2 observations. Our regional mean a posteriori combustion CO2 emission ranges from 4.6–5.0 Gta-1 (1.5 %–2.4 % relative standard deviation), with all inversions reporting an overestimate for Germany's wintertime emissions. Our national a posteriori CO2 combustion emissions are highly dependent on the assumed relationship between CO2 and CO uncertainties, as expected. Generally, we find better results when we use grid-scale-based a priori CO2:CO uncertainty estimates rather than a fixed relationship between the two species. [ABSTRACT FROM AUTHOR]

We present measurements of volatile organic compounds (VOCs) and other trace gases taken in Salt Lake City, Utah in August and September 2022. As part of the Salt Lake regional Smoke, Ozone and Aerosol Study (SAMOZA), 35 VOCs were measured with two methods: a proton‐transfer‐reaction time‐of‐flight mass spectrometer (PTR‐ToF‐MS) and 2,4‐dinitrophenylhydrazine (DNPH) cartridges analyzed by high‐performance liquid chromatography (HPLC). Over two months, the total measured VOCs averaged 32 ± 24 ppb (mean ± standard deviation) with the hourly maximum at 141 ppb, and the total calculated OH reactivity averaged 3.7 ± 3.0 s−1 (maximum at 20.7 s−1). Among them, methanol and ethanol were the most abundant VOCs, making up 42% of the ambient mixing ratio. Isoprene and monoterpenes contributed 25% of the OH reactivity from VOCs, while formaldehyde and acetaldehyde made up another 30%. The positive matrix factorization analysis showed 5 major sources of VOCs, with 32% of abundance being attributed to secondary production/biogenic sources, 44% from the combination of traffic and personal care products, 15% from industrial solvent use, and the rest from biomass burning (10%). Moderate smoke‐impacted days elevated various hazardous air pollutants (HAPs) on average by 45%–217% compared to smoke‐free days. The ratio of OH reactivity from NOx to that from VOCs showed that ozone production was mostly VOC‐limited throughout the campaign, consistent with our modeling study. VOCs and NOx both showed increased OH reactivity due to smoke influence. NOx featured increased reactivity on weekdays compared to weekends, an effect not shown for VOC reactivity during SAMOZA. Plain Language Summary: Salt Lake City, Utah has higher concentrations of ozone, a pollutant harmful to human and plant life, in the atmosphere than the standard set by the United States Environmental Protection Agency (US EPA). The reasons for the high levels of ozone remain uncertain. Volatile organic compounds (VOCs) are a class of air pollutants that undergo reactions that produce ozone. Understanding their sources and reactions is important to be able to reduce air pollution. In this study, we measured 35 VOCs in SLC in August and September 2022 and used a model to identify their major sources. Concentrations of hazardous VOCs identified by the US EPA increased by 45%–217% when wildfire smoke was present in the air. Methanol and ethanol were the most important VOCs in terms of total concentration in the air, while isoprene and monoterpenes were the most important in terms of reactions that could create ozone. According to the model results, VOCs are emitted from five major sources including traffic and solvent use. Further measurements are needed to confirm the model results and reduce uncertainty of the important sources of VOCS. Key Points: Methanol and ethanol dominated the total measured VOC abundance while isoprene dominated total OH reactivity from volatile organic compounds (VOCs) in Salt Lake CityTraffic and solvent use are roughly equivalent contributors to anthropogenic VOC emissions in Salt Lake City during SAMOZAOzone production was limited by VOCs in Salt Lake City in summer 2022 [ABSTRACT FROM AUTHOR]

Improved urban greenhouse gas (GHG) flux estimates are crucial for informing policy and mitigation efforts. Atmospheric inversion modeling (AIM) is a widely used technique combining atmospheric measurements of trace gas, meteorological modeling, and a prior emission map to infer fluxes. Traditionally, AIM relies on mid‐afternoon observations due to the well‐represented atmospheric boundary layer in meteorological models. However, confining flux assessment to daytime observations is problematic for the urban scale, where air masses typically move over a city in a few hours and AIM therefore cannot provide improved constraints on emissions over the full diurnal cycle. We hypothesized that there are atmospheric conditions beyond the mid‐afternoon under which meteorological models also perform well. We tested this hypothesis using tower‐based measurements of CO2 and CH4, wind speed observations, weather model outputs from INFLUX (Indianapolis Flux Experiment), and a prior emissions map. By categorizing trace gas vertical gradients according to wind speed classes and identifying when the meteorological model satisfactorily simulates boundary layer depth (BLD), we found that non‐afternoon observations can be assimilated when wind speed is >5 m/s. This condition resulted in small modeled BLD biases (<40%) when compared to calmer conditions (>100%). For Indianapolis, 37% of the GHG measurements meet this wind speed criterion, almost tripling the observations retained for AIM. Similar results are expected for windy cities like Auckland, Melbourne, and Boston, potentially allowing AIM to assimilate up to 60% of the total (24‐hr) observations. Incorporating these observations in AIMs should yield a more diurnally comprehensive evaluation of urban GHG emissions. Plain Language Summary: It is crucial to improve greenhouse gas (GHG) emission estimates to inform policy and mitigation strategies. However, the current model techniques used to estimate such emissions rely on incorporating only mid‐afternoon observations of atmospheric concentrations of GHGs. For cities, this limits a detailed understanding of emissions during hours of the day when emissions are the highest, such as the morning rush hours. This constraint is due to the limitations on how well meteorological models can describe the atmosphere during stable conditions, such as when calm winds prevail. To understand if there are any atmospheric conditions when meteorological models have good performance, for non‐afternoon hours, we used atmospheric measurements of carbon dioxide and methane, alongside meteorological model outputs. We found that observations during non‐afternoon hours are suitable for use in models when wind speed is greater than 5 m/s. This means that it is possible to double the amount of data that goes into the modeled GHG emission estimates. With this finding, emission estimates will potentially be improved, leading to a better evaluation of the diurnal cycle of GHG emissions. Key Points: Assimilating non‐afternoon greenhouse gas (GHG) observations in atmospheric inversions is reliable when wind speeds are greater than 5 m/sInclusion of non‐afternoon atmospheric observations during windy conditions doubles the current data assimilation in atmospheric inversionsAdditional observations in atmospheric inversions have the potential to improve GHG emissions estimates [ABSTRACT FROM AUTHOR]

We report new radio observations of SDSS J090122.37+181432.3, a strongly lensed star-forming galaxy at z = 2.26. We image 1.4 GHz (L -band) and 3 GHz (S -band) continuum using the Very Large Array (VLA) and 1.2 mm (band 6) continuum with Atacama Large Millimeter/submillimeter Array, in addition to the CO(7–6) and C i (3 P 2→3 P 1) lines, all at ≲1.″7 resolution. Based on the VLA integrated flux densities, we decompose the radio spectrum into its free–free (FF) and nonthermal components. The infrared–radio correlation parameter q TIR = 2.65 − 0.31 + 0.24 is consistent with expectations for star-forming galaxies. We obtain radio continuum-derived star formation rates (SFRs) that are free of dust extinction, finding 620 − 220 + 280 M ⊙ yr − 1 , 230 − 160 + 570 M ⊙ yr − 1 , and 280 − 120 + 460 M ⊙ yr − 1 from the FF emission, nonthermal emission, and when accounting for both emission processes, respectively, in agreement with previous results. We estimate the gas mass from the C i (3 P 2→3 P 1) line as M gas = (1.2 ± 0.2) × 1011 M ☉, which is consistent with prior CO(1–0)-derived gas masses. Using our new IR and radio continuum data to map the SFR, we assess the dependence of the Schmidt–Kennicutt relation on choices of SFR and gas tracer for ∼kpc scales. The different SFR tracers yield different slopes, with the IR being the steepest, potentially due to highly obscured star formation in J0901. The radio continuum maps have the lowest slopes and overall fidelity for mapping the SFR, despite producing consistent total SFRs. We also find that the Schmidt–Kennicutt relation slope is flattest when using CO(7–6) or C i (3 P 2→3 P 1) to trace gas mass, suggesting that those transitions are not suitable for tracing the bulk molecular gas in galaxies like J0901. [ABSTRACT FROM AUTHOR]

Optical fiber sensor emerges as a highly promising technology for trace gas detection due to their high sensitivity, remote capability, and immunity to electromagnetic interference. However, the state‐or‐the‐art fiber‐optic gas sensors typically use lengthy optical fibers as gas absorption cells or coatings with functional materials to achieve more sensitive gas detection, which poses challenges such as slow response and/or poor selectivity, as well as limitations on their use in confined spaces. Here, an ultraminiature optical fiber‐tip photothermal gas sensor via direct 3D micro‐printing of a Fabry‐Pérot cavity on the end face of a standard single‐mode optical fiber is reported. It enables not only direct interaction between light and gas molecules at the fiber output but also remote interrogation through an interferometric read‐out scheme. With a low‐finesse microcavity of 66 µm in length, a noise equivalent concentration of 160 parts‐per‐billion acetylene gas is demonstrated with an ultra‐fast response time of 0.5 s. Such a small high‐performance photothermal gas sensor offers an approach to remotely detecting trace gases for a myriad of applications ranging from in‐reactor monitoring to medical diagnosis. [ABSTRACT FROM AUTHOR]

Biomass burning (BB) is a major source of trace gases and particles in the atmosphere, influencing air quality, radiative balance, and climate. Previous studies have mainly focused on the BB emissions of carbon and nitrogen species with less attention on chlorine. Reactive chlorine chemistry has significant effects on atmospheric chemistry and air quality. However, quantitative information on chlorine emissions from BB, particularly the long-term trend and associated atmospheric impacts, is limited both on regional and global scales. Here, we report a long-term (2001–2018) high-resolution BB emission inventory for the major chlorine-containing compounds (HCl, chloride, and CH3Cl) in Asia based on satellite observations. We estimate an average of 730 Gg yr−1 chlorine emitted from BB activity in Asia, with China contributing the largest share at 24.2% (177 Gg yr−1), followed by Myanmar at 18.7% and India at 18.3%. Distinct seasonal patterns and significant spatial and interannual variability are observed, mainly driven by human-mediated changes in agricultural activity. By incorporating the newly developed chlorine emission inventory into a global chemistry-climate model (CAM-Chem), we find that the BB-chlorine emissions lead to elevated levels of HCl and CH3Cl (monthly average up to 2062 and 1421 parts per trillion by volume (pptv), respectively), subsequently resulting in noticeable changes in oxidants (up to 3.1% in O3 and 17% in OH radicals). The results demonstrate that BB is not only a significant source of air pollutants but also of oxidants, suggesting a larger role of BB emissions in the atmospheric chemistry and oxidation process than previously appreciated. In light of the projected increase in BB activity toward the end of the century and the extensive control of anthropogenic emissions worldwide, the contribution of BB emissions may become fundamental to air quality composition in the future. [ABSTRACT FROM AUTHOR]

European Space Agency's Mars Express (MEX) has been orbiting Mars for 20 years and its instruments have provided a plethora of observations of atmospheric dust and clouds. These observations have been analysed to produce many unique views of the processes leading to dust lifting and cloud formation, and a full picture of the climatologies of dust and clouds has emerged. Moreover, the orbit of MEX enables viewing the planet at many local times, giving a unique access to the diurnal variations of the atmosphere. This article provides an overview of the observations of dust and clouds on Mars by MEX, complemented by the Trace Gas Orbiter that has been accompanying MEX on orbit for some years. [ABSTRACT FROM AUTHOR]

The exchange of momentum, heat and trace gases between atmosphere and surface is mainly controlled by turbulent fluxes. Turbulent mixing is usually parametrized using Monin–Obukhov similarity theory (MOST), which was derived for steady turbulence over homogeneous and flat surfaces, but is nevertheless routinely applied to unsteady turbulence over non-homogeneous surfaces. We study four years of eddy-covariance measurements at a highly heterogeneous alpine valley site in Finse, Norway, to gain insights into the validity of MOST, the turbulent transport mechanisms and the contributing coherent structures. The site exhibits a bimodal topography-following flux footprint, with the two dominant wind sectors characterized by organized and strongly negative momentum flux, but different anisotropy and contributions of submeso-scale motions, leading to a failure of eddy-diffusivity closures and different transfer efficiencies for different scalars. The quadrant analysis of the momentum flux reveals that under stable conditions sweeps transport more momentum than the more frequently occurring ejections, while the opposite is observed under unstable stratification. From quadrant analysis, we derive the ratio of the amount of disorganized to organized structures, that we refer to as organization ratio (OR). We find an invertible relation between transfer efficiency and corresponding organization ratio with an algebraic sigmoid function. The organization ratio further explains the scatter around scaling functions used in MOST and thus indicates that coherent structures modify MOST. Our results highlight the critical role of coherent structures in turbulent transport in heterogeneous tundra environments and may help to find new parametrizations for numerical weather prediction or climate models. [ABSTRACT FROM AUTHOR]

The Earth's atmosphere is composed of an enormous variety of chemical species associated with trace gases and aerosol particles whose composition and chemistry have critical impacts on the Earth's climate, air quality, and human health. Mass spectrometry analysis as a powerful and popular analytical technique has been widely developed and applied in atmospheric chemistry for decades. Mass spectrometry allows for effective detection, identification, and quantification of a broad range of organic and inorganic chemical species with high sensitivity and resolution. In this review, we summarize recently developed mass spectrometry techniques, methods, and applications in atmospheric chemistry research in the past several years on molecular‐level. Specifically, new developments of ion‐molecule reactors, various soft ionization methods, and unique coupling with separation techniques are highlighted. The new mass spectrometry applications in laboratory studies and field measurements focused on improving the detection limits for traditional and emerging volatile organic compounds, characterizing multiphase highly oxygenated molecules, and monitoring particle bulk and surface compositions. [ABSTRACT FROM AUTHOR]

Black-carbon-containing (BCc) particles are ubiquitous in ambient air, significantly contributing to particulate matter (PM) pollution. The unexpected outbreak of the COVID-19 pandemic in the summer of 2021 prompted a localized and prolonged lockdown in Yangzhou, situated in the Yangtze River Delta, China. This lockdown led to significant alteration of local anthropogenic emissions, while neighboring cities continued regular operations, providing a unique opportunity for the investigation of BCc particle characteristics influenced by varying emission conditions. Single-particle aerosol mass spectrometer (SPA-MS) analysis revealed a notable decrease in the proportion of freshly emitted BCc particles during the lockdown (LD) period. However, PM 2.5 concentrations remained relatively unchanged, with an observed increase in the proportion of aged BCc particles during LD compared to the period before the lockdown (BLD). The study also underscores the significant role of regional transport in PM 2.5 pollution during the campaign. Moreover, reactive trace gases (e.g., NOx , SO2 , and volatile organic compounds – VOCs) could form thick coatings on pre-existing particles, likely via enhanced heterogeneous hydrolysis under high relative humidity (RH), resulting in significant BCc particle growth (∼ 600 nm), as well as PM 2.5 concentration, during LD. Our study highlights that short-term, strict local emission controls may not effectively reduce PM pollution due to the complex production and transmission characteristics of BCc particles and the nonlinear responses of PM 2.5 to its precursors. Achieving further effective PM 2.5 reduction mandates a focus on nuanced control of BCc particles and necessitates a comprehensive and extensive approach with a regionally coordinated and balanced control strategy through joint regulation. [ABSTRACT FROM AUTHOR]

Emissions from biomass burning are a significant source of air pollution, which can adversely impact air quality and ecosystems thousands of kilometres downwind. These emissions can be estimated by a bottom-up approach that relies on fuel consumed and standardized emission factors. Emissions are also commonly derived with a top-down approach, using satellite-observed fire radiative power (FRP) as a proxy for fuel consumption. Biomass burning emissions can also be estimated directly from satellite trace gas observations, including carbon monoxide (CO). Here, we explore the potential of satellite-derived CO emission rates from biomass burning and provide new insights into the understanding of satellite-derived fire CO emissions globally, with respect to differences in regions and vegetation type. Specifically, we use the TROPOMI (Tropospheric Monitoring Instrument) high-spatial-resolution satellite datasets to derive burning CO emissions directly for individual fires between 2019 and 2021 globally. Using synthetic data (with known emissions), we show that the direct emission estimate methodology has a 34 % uncertainty for deriving CO emissions (and a total uncertainty of 44 % including wind and CO column uncertainty). From the TROPOMI-derived CO emissions, we derive biome-specific emission coefficients (emissions relative to FRP) by combining the direct emission estimates and the satellite-observed FRP from the Moderate Resolution Imaging Spectrometer (MODIS). These emission coefficients are used to establish annual top-down CO emission inventories from biomass burning, showing that Southern Hemisphere Africa has the highest CO biomass burning emissions (over 25 % of global total of 300–390 Mt(CO) yr -1 between 2003–2021), and almost 25 % of global CO biomass burning emissions are from broadleaved evergreen tree fires. A comprehensive comparison between direct estimates, top-down and bottom-up approaches, provides insight into the strengths and weaknesses of each method: FINN2.5 has higher CO emissions, by a factor between 2 and 5, than all other inventories assessed in this study. Trends over the past 2 decades are examined for different regions around the globe, showing that global CO biomass burning emissions have, on the whole, decreased (by 5.1 to 8.7 Mt(CO) yr -1), where some regions experience increased and others decreased emissions. [ABSTRACT FROM AUTHOR]

Hydration of the stratosphere by tropopause‐overshooting convection has received increasing interest due to the extreme concentrations of water vapor that can result and, ultimately, the climate warming potential such hydration provides. Previous work has recognized the importance of numerous dynamic and physical processes that control stratospheric water vapor delivery by convection. This study leverages recent comprehensive observations from the NASA Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign to determine the frequency at which each process operates during real events. Specifically, a well‐established analysis technique known as tracer‐tracer correlation is applied to DCOTSS observations of ozone, water vapor, and potential temperature to identify the occurrence of known processes. It is found that approximately half of convectively‐driven stratospheric hydration samples show no indication of significant air mass transport and mixing, emphasizing the importance of ice sublimation to stratospheric water vapor delivery. Furthermore, the temperature of the upper troposphere and lower stratosphere environment and/or overshoot appears to be a commonly active constraint, since the approximate maximum possible water vapor concentration that can be reached in an air mass is limited to the saturation mixing ratio when ice is present. Finally, little evidence of relationships between dynamic and physical processes and their spatial distribution was found, implying that stratospheric water vapor delivery by convection is likely facilitated by a complex collection of processes in each overshooting event. Plain Language Summary: Thunderstorms are capable of transporting air and water up to the second layer of Earth's atmosphere, the stratosphere. Resulting irreversible modifications to greenhouse gases that regulate climate, such as water vapor and ozone, are important to quantify and poorly understood. This study uses recently‐obtained aircraft observations to improve understanding of irreversible transport in thunderstorms and the environmental and storm factors that control it. By examining how multiple trace gases and other quantities co‐vary, it is found that half of observed stratospheric changes by thunderstorms only exhibit increases in water vapor, which is argued to be driven by transported ice. It is also found that the environmental temperature is an important constraint in any storm because it limits the amount of stratospheric water vapor change that can occur. Key Points: Recent airborne observations reveal key dynamic and physical processes controlling the stratospheric delivery of water vapor by convectionIn situ observations suggest that water vapor is delivered routinely via both air transport and ice sublimationTemperature is an important constraint for water vapor delivery in any stratospheric environment [ABSTRACT FROM AUTHOR]

We use measurements of trace gases from the Microwave Limb Sounder and polar stratospheric clouds (PSCs) from the Cloud‐Aerosol Lidar with Orthogonal Polarization to investigate how the extraordinary stratospheric water vapor enhancement from the 2022 Hunga eruption affected polar processing during the 2023 Antarctic winter. Although the dynamical characteristics of the vortex itself were generally unexceptional, the excess moisture initially raised PSC formation threshold temperatures above typical values. Cold conditions, especially in early July, prompted ice PSC formation and unusually severe irreversible dehydration at higher levels (500–700 K), while atypical hydration occurred at lower levels (380–460 K). Heterogeneous chemical processing was more extensive, both vertically (up to 750–800 K) and temporally (earlier in the season), than in prior Antarctic winters. The resultant HCl depletion and ClO enhancement redefined their previously observed ranges at and above 600 K. Albeit unmatched in the satellite record, the early‐winter upper‐level chlorine activation was insufficient to induce substantial ozone loss. Chlorine activation, denitrification, and dehydration processes ran to completion by July/August, with trace gas evolution mostly following the climatological mean thereafter, but with chlorine deactivation starting slightly later than usual. While cumulative ozone losses at 410–550 K were relatively large, probably because of the delayed chlorine deactivation, they were not unprecedented. Thus, ozone depletion was unremarkable throughout the lower stratosphere. Although Hunga enhanced PSC formation and chemical processing in early winter, saturation of lower stratospheric denitrification, dehydration, and chlorine activation (as is typical in the Antarctic) prevented an exceptionally severe ozone hole in 2023. Plain Language Summary: The 2022 eruption of the Hunga volcano produced an increase in stratospheric water vapor unmatched in the satellite record. Excess moisture pervaded the Antarctic stratosphere at the beginning of the 2023 Southern Hemisphere winter. Cold moist conditions prompted formation of ice clouds in the Antarctic stratosphere at higher altitudes than usual. Falling ice particles caused unusually severe permanent removal of water vapor from these levels and deposited it at lower altitudes. Chemical processing on polar stratospheric cloud particles occurred both earlier in the season and over a broader vertical domain than typical, resulting in exceptional early‐winter upper‐level conversion of chlorine from nonreactive into ozone‐destroying forms. Chemical processing ran its course by midwinter (i.e., July/August), with trace gases, including ozone, mostly following average behavior thereafter. Deactivation (reconversion of chlorine into nonreactive forms) started slightly later than in most years. While cumulative seasonal ozone losses were relatively large at some levels, probably because of the delayed chlorine deactivation, they were not unprecedented. Thus, although Hunga accelerated and expanded the vertical extent of chemical processing in early winter, that chemical processing reached completion as usually happens in Antarctic midwinter, preventing an extraordinarily severe ozone hole in 2023. Key Points: Hydration from Hunga led to unusually early and vertically extensive polar stratospheric cloud activity in the 2023 Antarctic vortexAs a result, heterogeneous chlorine activation occurred weeks earlier and at higher altitudes and dehydration removed more H2O than typicalDespite exceptional early‐winter conditions, cumulative ozone losses were unremarkable because stratospheric chemical processing saturated [ABSTRACT FROM AUTHOR]

Highlights: Exploiting single-atom catalytic activation and targeted adsorption properties, Ni single-atom active sites based on N, C coordination are constructed on the surface of two-dimensional MXene nanosheets (Ni–N–C/Ti3C2Tx), enabling highly sensitive and selective NH3 gas detection. The catalytic activation effect of Ni–N–C/Ti3C2Tx effectively reduces the Gibbs free energy of the sensing elemental reaction, while its electronic structure promotes the spill-over effect of reactive oxygen species at the gas–solid interface. An end-sealing passivation strategy utilizing a conjugated hydrogen bond network of the conductive polymer was employed on MXene-based flexible electrodes, effectively mitigating the oxidative degradation of MXene-based gas sensors. Significant challenges are posed by the limitations of gas sensing mechanisms for trace-level detection of ammonia (NH3). In this study, we propose to exploit single-atom catalytic activation and targeted adsorption properties to achieve highly sensitive and selective NH3 gas detection. Specifically, Ni single-atom active sites based on N, C coordination (Ni–N–C) were interfacially confined on the surface of two-dimensional (2D) MXene nanosheets (Ni–N–C/Ti3C2Tx), and a fully flexible gas sensor (MNPE–Ni–N–C/Ti3C2Tx) was integrated. The sensor demonstrates a remarkable response value to 5 ppm NH3 (27.3%), excellent selectivity for NH3, and a low theoretical detection limit of 12.1 ppb. Simulation analysis by density functional calculation reveals that the Ni single-atom center with N, C coordination exhibits specific targeted adsorption properties for NH3. Additionally, its catalytic activation effect effectively reduces the Gibbs free energy of the sensing elemental reaction, while its electronic structure promotes the spill-over effect of reactive oxygen species at the gas–solid interface. The sensor has a dual-channel sensing mechanism of both chemical and electronic sensitization, which facilitates efficient electron transfer to the 2D MXene conductive network, resulting in the formation of the NH3 gas molecule sensing signal. Furthermore, the passivation of MXene edge defects by a conjugated hydrogen bond network enhances the long-term stability of MXene-based electrodes under high humidity conditions. This work achieves highly sensitive room-temperature NH3 gas detection based on the catalytic mechanism of Ni single-atom active center with N, C coordination, which provides a novel gas sensing mechanism for room-temperature trace gas detection research. [ABSTRACT FROM AUTHOR]

Odd-hydrogen (HO |$_\mathrm{x}$|⁠) species have a crucial role in regulating the chemistry of the atmosphere of Mars and are important to understand some of the most fundamental aspects regarding its atmospheric composition such as the long-term stability of CO |$_2$|⁠. Despite the key role of these species for our understanding of the Martian photochemistry, there is little observational evidence constraining their abundances. In this study, we use infrared solar occultation observations from the Atmospheric Chemistry Suite aboard the ExoMars Trace Gas Orbiter to search for spectral signatures of HO |$_2$| in the atmosphere of Mars. In our analysis of the data, we retrieve vertical profiles of pressure, temperature, and water vapour mixing ratio, but are unable to confidently detect the presence of HO |$_2$| features in the spectra. We report upper limits of 15 ppbv (5 |$\sigma$|⁠), which represents an order of magnitude improvement with respect to previous investigations. Comparing the derived upper limits with the expectations from 3-dimensional Global Climate Models, we find that approximately an order of magnitude improvement in the instrument sensitivity would be required to detect this molecule and/or constrain the models. [ABSTRACT FROM AUTHOR]

Molecular identification of volatile organic compounds (VOCs) plays an important role in various applications including environmental monitoring and smart farming. Mid‐infrared (MIR) fingerprint absorption spectroscopy is a powerful tool to extract chemical‐specific features for gas identification. However, the detection and recognition of trace VOC gas mixtures remain challenging due to their intrinsic weak light–matter interaction and highly overlapped absorption spectra. Here, an artificial intelligence‐enhanced “photonic nose” for MIR spectroscopic analysis of trace VOC gas mixtures is proposed. To enhance the sensing performance by increasing bandwidth and sensitivity, the “photonic nose” is designed to employ coupled multi‐resonant plasmonic nanoantennas to cover MIR molecular fingerprints, coated with metal–organic frameworks as the gas enrichment layer. Low limits of detection are achieved (IPA: 1.99 ppm, ethanol: 3.43 ppm, and acetone: 9.82 ppm). With machine learning, a high classification accuracy of 100% is realized for 125 mixing ratios (IPA, ethanol: both 5 concentrations, 0–130 ppm; acetone: 5 concentrations, 0–201 ppm), and low‐deviation component concentration predictions of root‐mean‐squared error within 10 ppm are achieved for IPA and ethanol (both 0–130 ppm) under interference from 50 ppm acetone. The work paves the way for intelligent sensing platforms for environmental monitoring and smart framing. [ABSTRACT FROM AUTHOR]

Accurately detecting atmospheric carbon dioxide is a vital part of responding to the global greenhouse effect. Conventional off-axis integral cavity detection systems are computationally intensive and susceptible to environmental factors. This study deploys an Extreme Learning Machine model incorporating a cascaded integrator comb (CIC) filter into the off-axis integrating cavity. It is shown that appropriate parameters can effectively improve the performance of the instrument in terms of lower detection limit, accuracy, and root mean square deviation. The proposed method is incorporated successfully into a monitoring station situated near an industrial area for detecting atmospheric carbon dioxide (CO2) concentration daily. [ABSTRACT FROM AUTHOR]