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The gas-phase reaction of isoprene with the nitrate radical (NO3) was investigated in experiments in the outdoor SAPHIR chamber under atmospherically relevant conditions specifically with respect to the chemical lifetime and fate of nitrato-organic peroxy radicals (RO2). Observations of organic products were compared to concentrations expected from different chemical mechanisms: (1) the Master Chemical Mechanism, which simplifies the NO3 isoprene chemistry by only considering one RO2 isomer; (2) the chemical mechanism derived from experiments in the Caltech chamber, which considers different RO2 isomers; and (3) the FZJ-NO3 isoprene mechanism derived from quantum chemical calculations, which in addition to the Caltech mechanism includes equilibrium reactions of RO2 isomers, unimolecular reactions of nitrate RO2 radicals and epoxidation reactions of nitrate alkoxy radicals. Measurements using mass spectrometer instruments give evidence that the new reactions pathways predicted by quantum chemical calculations play a role in the NO3 oxidation of isoprene. Hydroperoxy aldehyde (HPALD) species, which are specific to unimolecular reactions of nitrate RO2, were detected even in the presence of an OH scavenger, excluding the possibility that concurrent oxidation by hydroxyl radicals (OH) is responsible for their formation. In addition, ion signals at masses that can be attributed to epoxy compounds, which are specific to the epoxidation reaction of nitrate alkoxy radicals, were detected. Measurements of methyl vinyl ketone (MVK) and methacrolein (MACR) concentrations confirm that the decomposition of nitrate alkoxy radicals implemented in the Caltech mechanism cannot compete with the ring-closure reactions predicted by quantum chemical calculations. The validity of the FZJ-NO3 isoprene mechanism is further supported by a good agreement between measured and simulated hydroxyl radical (OH) reactivity. Nevertheless, the FZJ-NO3 isoprene mechanism needs further investigations with respect to the absolute importance of unimolecular reactions of nitrate RO2 and epoxidation reactions of nitrate alkoxy radicals. Absolute concentrations of specific organic nitrates such as nitrate hydroperoxides would be required to experimentally determine product yields and branching ratios of reactions but could not be measured in the chamber experiments due to the lack of calibration standards for these compounds. The temporal evolution of mass traces attributed to product species such as nitrate hydroperoxides, nitrate carbonyl and nitrate alcohols as well as hydroperoxy aldehydes observed by the mass spectrometer instruments demonstrates that further oxidation by the nitrate radical and ozone at atmospheric concentrations is small on the timescale of one night (12 h) for typical oxidant concentrations. However, oxidation by hydroxyl radicals present at night and potentially also produced from the decomposition of nitrate alkoxy radicals can contribute to their nocturnal chemical loss.

Photochemical processes in ambient air were studied using the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich, Germany. Ambient air was continuously drawn into the chamber through a 50 m high inlet line and passed through the chamber for 1 month in each season throughout 2019. The residence time of the air inside the chamber was about 1 h. As the research center is surrounded by a mixed deciduous forest and is located close to the city Jülich, the sampled air was influenced by both anthropogenic and biogenic emissions. Measurements of hydroxyl (OH), hydroperoxyl (HO2), and organic peroxy (RO2) radicals were achieved by a laser-induced fluorescence instrument. The radical measurements together with measurements of OH reactivity (kOH, the inverse of the OH lifetime) and a comprehensive set of trace gas concentrations and aerosol properties allowed for the investigation of the seasonal and diurnal variation of radical production and destruction pathways. In spring and summer periods, median OH concentrations reached 6 × 106 cm−3 at noon, and median concentrations of both HO2 and RO2 radicals were 3 × 108 cm−3. The measured OH reactivity was between 4 and 18 s−1 in both seasons. The total reaction rate of peroxy radicals with NO was found to be consistent with production rates of odd oxygen (Ox= NO2 + O3) determined from NO2 and O3 concentration measurements. The chemical budgets of radicals were analyzed for the spring and summer seasons, when peroxy radical concentrations were above the detection limit. For most conditions, the concentrations of radicals were mainly sustained by the regeneration of OH via reactions of HO2 and RO2 radicals with nitric oxide (NO). The median diurnal profiles of the total radical production and destruction rates showed maxima between 3 and 6 ppbv h−1 for OH, HO2, and RO2. Total ROX (OH, HO2, and RO2) initiation and termination rates were below 3 ppbv h−1. The highest OH radical turnover rate of 13 ppbv h−1 was observed during a high-temperature (max. 40 ∘C) period in August. In this period, the highest HO2, RO2, and ROX turnover rates were around 11, 10, and 4 ppbv h−1, respectively. When NO mixing ratios were between 1 and 3 ppbv, OH and HO2 production and destruction rates were balanced, but unexplained RO2 and ROX production reactions with median rates of 2 and 0.4 ppbv h−1, respectively, were required to balance their destruction. For NO mixing ratios above 3 ppbv, the peroxy radical reaction rates with NO were highly uncertain due to the low peroxy radical concentrations close to the limit of NO interferences in the HO2 and RO2 measurements. For NO mixing ratios below 1 ppbv, a missing source for OH and a missing sink for HO2 were found with maximum rates of 3.0 and 2.0 ppbv h−1, respectively. The missing OH source likely consisted of a combination of a missing inter-radical HO2 to OH conversion reaction (up to 2 ppbv h−1) and a missing primary radical source (0.5–1.4 ppbv h−1). The dataset collected in this campaign allowed analyzing the potential impact of OH regeneration from RO2 isomerization reactions from isoprene, HO2 uptake on aerosol, and RO2 production from chlorine chemistry on radical production and destruction rates. These processes were negligible for the chemical conditions encountered in this study.

Nighttime NO3-initiated oxidation of biogenic volatile organic compounds (BVOCs) such as monoterpenes is important for the atmospheric formation and growth of secondary organic aerosol (SOA), which has significant impact on climate, air quality, and human health. In such SOA formation and growth, highly oxygenated organic molecules (HOM) may be crucial, but their formation pathways and role in aerosol formation have yet to be clarified. Among monoterpenes, limonene is of particular interest for its high emission globally and high SOA yield. In this work, HOM formation in the reaction of limonene with nitrate radical (NO3) was investigated in the SAPHIR chamber (Simulation of Atmospheric PHotochemistry In a large Reaction chamber). About 280 HOM products were identified, grouped into 19 monomer families, 11 dimer families, and 3 trimer families. Both closed-shell products and open-shell peroxy radicals (RO2⚫) were observed, and many of them have not been reported previously. Monomers and dimers accounted for 47 % and 47 % of HOM concentrations, respectively, with trimers making up the remaining 6 %. In the most abundant monomer families, C10H15−17NO6−14, carbonyl products outnumbered hydroxyl products, indicating the importance of RO2⚫ termination by unimolecular dissociation. Both RO2⚫ autoxidation and alkoxy–peroxy pathways were found to be important processes leading to HOM. Time-dependent concentration profiles of monomer products containing nitrogen showed mainly second-generation formation patterns. Dimers were likely formed via the accretion reaction of two monomer RO2⚫, and HOM-trimers via the accretion reaction between monomer RO2⚫ and dimer RO2⚫. Trimers are suggested to play an important role in new particle formation (NPF) observed in our experiment. A HOM yield of 1.5%-0.7%+1.7% was estimated considering only first-generation products. SOA mass growth could be reasonably explained by HOM condensation on particles assuming irreversible uptake of ultra-low volatility organic compounds (ULVOCs), extremely low volatility organic compounds (ELVOCs), and low volatility organic compounds (LVOCs). This work provides evidence for the important role of HOM formed via the limonene +NO3 reaction in NPF and growth of SOA particles.

Although anthropogenic emissions have decreased during the last two decades, air pollution is still problematic in many regions in Europe. In 2021, the World Health Organisation has released updated air quality guideline levels that base on newest medical research and have drastically decreased in comparison to the previous levels, except for SO2. These levels reflect the minimum concentration for which evidence of adverse health effects have been found. This study analyses the air quality in Europe using simulations by EURAD-IM for the year 2016 with optimized emissions to evaluate guideline exceedances for PM2.5, NO2, and O3. All air pollutant concentrations in Europe exceed the WHO2021 annual guideline levels by a large amount. High PM2.5 and O3 concentrations are homogeneously distributed across Europe with 99 % and 100 % of the EU38 population (European Union and eleven other European states) exposed to concentrations above the guideline levels. High NO2 concentrations are linked to densely populated areas. However, 61% of the EU38 population is exposed to concentrations above the guideline level. For PM2.5, the effect of different aerosol classes on the bulk mass and different PM reduction scenarios are analysed. NO3- shows the largest contribution to total PM2.5 while primary anthropogenic aerosols are mainly responsible for extremely high PM2.5 concentrations of up to 30 μg m−3. In the extreme case of completely removing different aerosol classes from the bulk mass, jointly removing NO3- and primary anthropogenic aerosols as well as removing all secondary inorganic aerosols decrease PM2.5 annual concentrations to below 5 μg m−3, which is the WHO2021 annual guideline level, in most parts of Europe. However, a more realistic scenario, in which the decrease of aerosol concentrations linearly follows the targeted anthropogenic emission reductions by the European Union, still shows an exceedance of the annual WHO2021 guideline levels by a factor of 2 - 3 throughout Europe. Thus, besides implementing strong emission reduction plans, other ways of removing air pollutants from the atmosphere need to be designed and implemented.

The oxidation of limonene by the hydroxyl (OH) radical and ozone (O3) was investigated in the atmospheric simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a large Reaction Chamber) in experiments performed at different nitric oxide (NO) mixing ratios from nearly 0 up to 10 ppbv. For the experiments dominated by OH oxidation, the formaldehyde (HCHO) yield was experimentally determined and found to be (12 ± 3), (13 ± 3), and (32 ± 5) % for experiments with low (∼ 0.1 ppbv), medium (∼ 0.3 ppbv), and high NO (5 to 10 ppbv), respectively. The yield in an ozonolysis-only experiment was (10 ± 1) %, which agrees with previous laboratory studies. The experimental yield of the first-generation organic nitrates from limonene–OH oxidation is calculated as (34 ± 5) %, about 11 % higher than the value in the Master Chemical Mechanism (MCM), which is derived from structure–activity relationships (SARs). Time series of measured radicals, trace-gas concentrations, and OH reactivity are compared to results from zero-dimensional chemical box model calculations applying MCM v3.3.1. Modeled OH reactivity is 5 to 10 s−1 (25 % to 33 % of the OH reactivity at the start of the experiment) higher than measured values at the end of the experiments under all chemical conditions investigated, suggesting either that there are unaccounted loss processes of limonene oxidation products or that products are less reactive toward OH. In addition, model calculations underestimate measured hydroperoxyl radical (HO2) concentrations by 20 % to 90 % and overestimate organic peroxyl radical (RO2) concentrations by 50 % to 300 %. The largest deviations are found in low-NO experiments and in the ozonolysis experiment. An OH radical budget analysis, which uses only measured quantities, shows that the budget is closed in most of the experiments. A similar budget analysis for RO2 radicals suggests that an additional RO2 loss rate constant of about (1–6) × 10−2 s−1 for first-generation RO2 is required to match the measured RO2 concentrations in all experiments. Sensitivity model runs indicate that additional reactions converting RO2 to HO2 at a rate constant of about (1.7–3.0) × 10−2 s−1 would improve the model–measurement agreement of NOx, HO2, and RO2 concentrations and OH reactivity. Reaction pathways that could lead to the production of additional OH and HO2 are discussed, which include isomerization reactions of RO2 from the oxidation of limonene, different branching ratios for the reaction of RO2 with HO2, and a faster rate constant for RO2 recombination reactions. As the exact chemical mechanisms of the additional HO2 and OH sources could not be identified, further work needs to focus on quantifying organic product species and organic peroxy radicals from limonene oxidation.

Atmospheric simulation chambers have been deployed with various research goals for more than 80 years. In this chapter, an overview of the various applications, including emerging new applications, is given. The chapter starts with a brief historical overview of atmospheric simulation chambers. It also provides an overview of how simulation chambers complement field observations and more classical laboratory experiments. The chapter is concluded with an introduction to the different aspects requiring consideration when designing an atmospheric simulation chamber.

Soot particles (SP) are ubiquitous components of atmospheric particulate matter and have been shown to cause various adverse health effects. In the atmosphere, freshly emitted SP can be coated by condensed low-volatility secondary organic and inorganic species. In addition, gas-phase oxidants may react with the surface of SP. Due to the chemical and physical resemblance of SP carbon backbone with polyaromatic hydrocarbon species and their potent oxidation products, we investigated the biological responses of BEAS-2B lung epithelial cells following exposure to fresh- and photochemically aged-SP at the air–liquid interface. A comprehensive physical and chemical aerosol characterization was performed to depict the atmospheric transformations of SP, showing that photochemical aging increased the organic carbon fraction and the oxidation state of the SP. RNA-sequencing and qPCR analysis showed varying gene expression profiles for fresh- and aged-SP. Exposure to aged-SP increased DNA damage, oxidative damage, and upregulation of NRF2-mediated oxidative stress response genes compared to fresh-SP. Furthermore, aged-SP augmented inflammatory cytokine secretion and activated AhR-response, as evidenced by increased expression of AhR-responsive genes. These results indicate that oxidative stress, inflammation, and DNA damage play a key role in the cytotoxicity of SP in BEAS-2B cells, where aging leads to higher toxic responses. Collectively, our results suggest that photochemical aging may increase SP toxicity through surface modifications that lead to an increased toxic response by activating different molecular pathways.

The photo-oxidation of myrcene, a monoterpene species emitted by plants, was investigated at atmospheric conditions in the outdoor simulation chamber SAPHIR (Simulation of Atmospheric PHotochemistry In a Large Reaction Chamber). The chemical structure of myrcene consists of one moiety that is a conjugated π system (similar to isoprene) and another moiety that is a triple-substituted olefinic unit (similar to 2-methyl-2-butene). Hydrogen shift reactions of organic peroxy radicals (RO2) formed in the reaction of isoprene with atmospheric OH radicals are known to be of importance for the regeneration of OH. Structure–activity relationships (SARs) suggest that similar hydrogen shift reactions like in isoprene may apply to the isoprenyl part of RO2 radicals formed during the OH oxidation of myrcene. In addition, SAR predicts further isomerization reactions that would be competitive with bimolecular RO2 reactions for chemical conditions that are typical for forested environments with low concentrations of nitric oxide. Assuming that OH peroxy radicals can rapidly interconvert by addition and elimination of O2 like in isoprene, bulk isomerization rate constants of 0.21 and 0.097 s−1 (T=298 K) for the three isomers resulting from the 3′-OH and 1-OH addition, respectively, can be derived from SAR. Measurements of radicals and trace gases in the experiments allowed us to calculate radical production and destruction rates, which are expected to be balanced. The largest discrepancies between production and destruction rates were found for RO2. Additional loss of organic peroxy radicals due to isomerization reactions could explain the observed discrepancies. The uncertainty of the total radical (ROx=OH+HO2+RO2) production rates was high due to the uncertainty in the yield of radicals from myrcene ozonolysis. However, results indicate that radical production can only be balanced if the reaction rate constant of the reaction between hydroperoxy (HO2) and RO2 radicals derived from myrcene is lower (0.9 to 1.6×10-11 cm3 s−1) than predicted by SAR. Another explanation of the discrepancies would be that a significant fraction of products (yield: 0.3 to 0.6) from these reactions include OH and HO2 radicals instead of radical-terminating organic peroxides. Experiments also allowed us to determine the yields of organic oxidation products acetone (yield: 0.45±0.08) and formaldehyde (yield: 0.35±0.08). Acetone and formaldehyde are produced from different oxidation pathways, so that yields of these compounds reflect the branching ratios of the initial OH addition to myrcene. Yields determined in the experiments are consistent with branching ratios expected from SAR. The yield of organic nitrate was determined from the gas-phase budget analysis of reactive oxidized nitrogen in the chamber, giving a value of 0.13±0.03. In addition, the reaction rate constant for myrcene + OH was determined from the measured myrcene concentration, yielding a value of (2.3±0.3)×10-10 cm3 s−1.

Photochemical processes in ambient air were studied using the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich, Germany. Ambient air was continuously drawn into the chamber through a 50 m high inlet line and passed through the chamber for 1 month in each season throughout 2019. The residence time of the air inside the chamber was about 1 h. As the research center is surrounded by a mixed deciduous forest and is located close to the city Jülich, the sampled air was influenced by both anthropogenic and biogenic emissions. Measurements of hydroxyl (OH), hydroperoxyl (HO2), and organic peroxy (RO2) radicals were achieved by a laser-induced fluorescence instrument. The radical measurements together with measurements of OH reactivity (kOH, the inverse of the OH lifetime) and a comprehensive set of trace gas concentrations and aerosol properties allowed for the investigation of the seasonal and diurnal variation of radical production and destruction pathways. In spring and summer periods, median OH concentrations reached 6 × 106 cm−3 at noon, and median concentrations of both HO2 and RO2 radicals were 3 × 108 cm−3. The measured OH reactivity was between 4 and 18 s−1 in both seasons. The total reaction rate of peroxy radicals with NO was found to be consistent with production rates of odd oxygen (Ox= NO2 + O3) determined from NO2 and O3 concentration measurements. The chemical budgets of radicals were analyzed for the spring and summer seasons, when peroxy radical concentrations were above the detection limit. For most conditions, the concentrations of radicals were mainly sustained by the regeneration of OH via reactions of HO2 and RO2 radicals with nitric oxide (NO). The median diurnal profiles of the total radical production and destruction rates showed maxima between 3 and 6 ppbv h−1 for OH, HO2, and RO2. Total ROX (OH, HO2, and RO2) initiation and termination rates were below 3 ppbv h−1. The highest OH radical turnover rate of 13 ppbv h−1 was observed during a high-temperature (max. 40 ∘C) period in August. In this period, the highest HO2, RO2, and ROX turnover rates were around 11, 10, and 4 ppbv h−1, respectively. When NO mixing ratios were between 1 and 3 ppbv, OH and HO2 production and destruction rates were balanced, but unexplained RO2 and ROX production reactions with median rates of 2 and 0.4 ppbv h−1, respectively, were required to balance their destruction. For NO mixing ratios above 3 ppbv, the peroxy radical reaction rates with NO were highly uncertain due to the low peroxy radical concentrations close to the limit of NO interferences in the HO2 and RO2 measurements. For NO mixing ratios below 1 ppbv, a missing source for OH and a missing sink for HO2 were found with maximum rates of 3.0 and 2.0 ppbv h−1, respectively. The missing OH source likely consisted of a combination of a missing inter-radical HO2 to OH conversion reaction (up to 2 ppbv h−1) and a missing primary radical source (0.5–1.4 ppbv h−1). The dataset collected in this campaign allowed analyzing the potential impact of OH regeneration from RO2 isomerization reactions from isoprene, HO2 uptake on aerosol, and RO2 production from chlorine chemistry on radical production and destruction rates. These processes were negligible for the chemical conditions encountered in this study.

Italy and Germany are establishing a new bilateral cooperation in meteorology, climatology and related disciplines that will create a hub of excellence for cutting edge research and translate the findings into improving operational services and university education. The joint research and education network IDEA-S4S will harness expertise of universities, research institutes and operational services in both countries and foster scientific exchange and collaboration to improve weather, climate and environmental services.Within the new programme, the core areas of scientific expertise of both countries will be systematically brought together, activities will be streamlined and extended beyond basic research collaboration to form a holistic IDEA-S4S network of weather and climate science and education, extending from qualification of graduates to support for early career researchers to networking of senior scientists. The programme will cooperate with WMO and the European Meteorological Infrastructure (ECMWF, EUMETSAT, EUMETNET) and strengthen the scientific environment for the ECMWF sites in Bonn and Bologna. A Joint Steering Committee will oversee the cooperation and guide the overall scientific and strategic direction of the programme.Through four-year funding periods, the network aims to make substantial progress in seamless high-resolution probabilistic Earth system prediction, employing state-of-the-art observing systems and Earth system models. This requires improved understanding and application of coupled processes between the components of the Earth system (including atmosphere-ocean-ice-land-vegetation-rivers) as well as between the impacts of human activities and the Earth system. Such complex weather and climate prediction systems place high demands on high-performance computing infrastructure, generate extremely large data volumes and need to integrate observations seamlessly into the models.In this contribution, we will present the concept and roadmap of the IDEA-S4S network, which will focus on improving seamless weather and climate forecasts, in particular for high impact events such as floods and droughts. Both countries have experienced devastating impacts of such extreme events with unusual rainfall intensities, some of which even lead to the destruction of entire regions. Better understanding the complex structure and the numerous feedback processes in such events will improve the prediction of future events in support of a better prepared and resilient society.

Ambient measurements of nitryl chloride (ClNO2) were performed at a rural site in Germany covering 3 periods in winter, summer, and autumn 2019 as part of the JULIAC campaign (Jülich Atmospheric Chemistry Project) that aimed for understanding the photochemical processes in air masses typical for mid-west Europe. Measurements were conducted at 50 m above ground, which was most located mainly at the nocturnal boundary layer and thus uncoupled from local surface emissions. ClNO2 is produced at nighttime by heterogeneous reaction of dinitrogen pentoxide (N2O5) on chloride ion (Cl-) containing aerosol. Its photolysis at day is of general interest as it produces chlorine (Cl) atoms that react with different atmospheric trace gases forming radicals. The highest observed ClNO2 mixing ratio was 1.6 ppbv (15-min average) in the middle of one night in September. Air masses reaching the measurement site either originated from long-range transport from the southwest and had an oceanic influence or circulated in the nearby region and were influenced by anthropogenic activities. Nocturnal maximum ClNO2 mixing ratios were around 0.2 ppbv if originating from long-range transport in nearly all seasons, while values were higher ranging from 0.4 to 0.6 ppbv for regionally influenced air. The chemical composition of long-range transported air was similar in all investigated seasons, while the regional air exhibited larger differences between the seasons. The N2O5 necessary for ClNO2 formation comes from the reaction of nitrate radicals (NO3) with nitrogen dioxide (NO2), where NO3 itself is formed by reaction of NO2 with ozone (O3). Measured concentrations of ClNO2, NO2 and O3 were used to quantify ClNO2 production efficiencies, i.e., the yield of ClNO2 formation per NO3 radical formed, and a box model was used to examine the idealized dependence of ClNO2 on the observed nocturnal O3 and NO2 concentrations. Results indicate that ClNO2 production efficiency was most sensitive to the availability of NO2 rather than that of O3 and increase with decreasing temperature. The average ClNO2 production efficiency was highest in February and September with values of 18 % and was lowest in December with values of 3 %. The average ClNO2 production efficiencies were in the range of 3 and 6 % from August to November for air masses originating from long-range transportation. These numbers are at the high end of values reported in literature indicating the importance of ClNO2 chemistry in rural environments in mid-west Europe.

Aromatic hydrocarbons are a class of volatile organic compounds associated with anthropogenic activity and make up a significant fraction of urban volatile organic compound (VOC) emissions that contribute to the formation of secondary organic aerosol (SOA). Benzene is one of the most abundant species emitted from vehicles, biomass burning and industry. An iodide time-of-flight chemical ionisation mass spectrometer (ToF-CIMS) and nitrate ToF-CIMS were deployed at the Julich Plant Atmosphere Chamber as part of a series of experiments examining benzene oxidation by OH under high- and low-NO x conditions, where a range of organic oxidation products were detected. The nitrate scheme detects many oxidation products with high masses, ranging from intermediate volatile organic compounds (IVOCs) to extremely low volatile organic compounds (ELVOCs), including C 12 dimers. In comparison, very few species with C ≥6 and O ≥8 were detected with the iodide scheme, which detected many more IVOCs and semi-volatile organic compounds (SVOCs) but very few ELVOCs and low volatile organic compounds (LVOCs). A total of 132 and 195 CHO and CHON oxidation products are detected by the iodide ToF-CIMS in the low- and high-NO x experiments respectively. Ring-breaking products make up the dominant fraction of detected signal and 21 and 26 of the products listed in the Master Chemical Mechanism (MCM) were detected. The time series of highly oxidised (O ≥6 ) and ring-retaining oxidation products (C 6 and double-bond equivalent = 4) equilibrate quickly, characterised by a square form profile, compared to MCM and ring-breaking products which increase throughout oxidation, exhibiting sawtooth profiles. Under low-NO x conditions, all CHO formulae attributed to radical termination reactions of first-generation benzene products, and first-generation auto-oxidation products are observed. Several N-containing species that are either first-generation benzene products or first-generation auto-oxidation products are also observed under high-NO x conditions. Hierarchical cluster analysis finds four clusters, of which two describe photo-oxidation. Cluster 2 shows a negative dependency on the NO 2 / NO x ratio, indicating it is sensitive to NO concentration and thus likely to contain NO addition products and alkoxy-derived termination products. This cluster has the highest average carbon oxidation state ( OS C ‾ ) and the lowest average carbon number. Where nitrogen is present in a cluster member of cluster 2, the oxygen number is even, as expected for alkoxy-derived products. In contrast, cluster 1 shows no dependency on the NO 2 / NO x ratio and so is likely to contain more NO 2 addition and peroxy-derived termination products. This cluster contains fewer fragmented species, as the average carbon number is higher and OS C ‾ lower than cluster 2, and more species with an odd number of oxygen atoms. This suggests that clustering of time series which have features pertaining to distinct chemical regimes, for example, NO 2 / NO x perturbations, coupled with a priori knowledge, can provide insight into identification of potential functionality.

Heterogeneous uptake of hydroperoxyl radicals (HO2) onto aerosols has been proposed to be a significant sink of HOx, hence impacting the atmospheric oxidation capacity. Accurate calculation of the HO2 uptake coefficient γHO2 is key to quantifying the potential impact of this atmospheric process. Laboratory studies show that γHO2 can vary by orders of magnitude due to changes in aerosol properties, especially aerosol soluble copper (Cu) concentration and aerosol liquid water content (ALWC). In this study we present a state-of-the-art model called MARK to simulate both gas- and aerosol-phase chemistry for the uptake of HO2 onto Cu-doped aerosols. Moreover, a novel parameterization of HO2 uptake was developed that considers changes in relative humidity (RH) and condensed-phase Cu ion concentrations and which is based on a model optimization using previously published and new laboratory data included in this work. This new parameterization will be applicable to wet aerosols, and it will complement current IUPAC recommendations. The new parameterization is as follows (the explanations for symbols are in the Appendix): 1γHO2=1αHO2+3×υHO24×106×RdHcorrRT×(5.87+3.2×ln⁡(ALWC/[PM]+0.067))×[PM]-0.2×Cu2+eff0.65+υHO2l4RTHorgDorgε. All parameters used in the paper are summarized in Table A1. Using this new equation, field data from a field campaign were used to evaluate the impact of the HO2 uptake onto aerosols on the ROx (= OH + HO2 + RO2) budget. Highly variable values for HO2 uptake were obtained for the North China Plain (median value

State of the art atmospheric chemistry transport models on regional scales as the EURAD-IM (EURopean Air pollution Dispersion-Inverse Model) simulate physical and chemical processes in the atmosphere to predict the dispersion of air pollutants. With EURAD-IM’s 4D-var data assimilation application, detailed analyses of the air quality can be conducted. These analyses allow for improvements of atmospheric chemistry forecast as well as emission source strength assessments. Simulations of EURAD-IM can be nested to a spatial resolution of 1 km, which does not correspond to the urban scale. Thus, inner city street canyon observations cannot be exploited since here, anthropogenic pollution vary vastly over scales of 100 m or less.We address this issue by implementing a machine learning (ML) module into EURAD-IM, forming a hybrid model that enable bridging the representativeness gap between model resolution and inner-city observations. Thus, the data assimilation of EURAD-IM is strengthened by additional observations in urban regions. Our approach of the ML module is based on a neural network (NN) with relevant environmental information of street architecture, traffic density, meteorology, and atmospheric pollutant concentrations from EURAD-IM as well as the street canyon observation of pollutants as input features. The NN then maps the observed concentration from street canyon scale to larger spatial scales.We are currently working with a fully controllable test environment created from EURAD-IM forecasts of the years 2020 and 2021 at different spatial resolutions. Here, the ML model maps the high-resolution hourly NO2 concentration to the concentration of the low resolution model grid. It turns out that it is very difficult for NNs to learn the hourly concentrations with equal accuracy using diurnal cycles of pollutant concentrations. Thus, we develop a model that uses an independent NN for each hour to support time-of-day learning. This allows to reduce the training error by a factor of 102. As a proof of concept, we trained the ML model in an overfitting regime where the mean squared training error reduce to 0.001% for each hour. Furthermore, by optimizing the hyperparameters and introducing regularization terms to reduce the overfitting, we achieved a validation error of 9−12% during night and 9−16% during day.

Ozonolysis of unsaturated hydrocarbons (VOCs) is one of the main oxidation processes in the atmosphere. The stabilized Criegee intermediates (SCI) formed are highly reactive oxygenated species that potentially influence the HOx, NOx and SOx cycles, and affect aerosol formation by yielding low-volatility oxygenated compounds. The current knowledge spans mostly SCI formed from primary emitted VOCs, but little is known about the reactivity of oxygenated SCI. In this work we present a theoretical kinetic study of a large number of unsaturated and oxygenated SCI, covering C[double bond, length as m-dash]C, OH, OR, OOH, OOOH, COOH, COOR, and ONO2 functionalities at various stereo- and site-specific substitutions relative to the SCI carbonyl oxide moiety. Several novel reaction types are covered, the most important of which are fast intramolecular insertion reactions in OH, OOH and COOH groups, or secondary ozonide formation with a COOH group, forming cyclic oxygenated species; these reaction classes are reminiscent of the analogous bimolecular reactions. The reaction with H2O molecules was likewise studied, finding that these cyclisation reactions can be catalysed, with predicted rate coefficients nearing the collision limit. The theoretical data is used to extend the structure–activity relationships (SARs) proposed by Vereecken et al. (2017), predicting the dominant unimolecular reaction class and rate, and the rates for reaction with H2O and (H2O)2. The SARs cover over 300 SCI categories with over 40 substituent categories. The validation of these SARs is discussed, and an outlook is given for further improvement. The generally short lifetime of oxygenated SCI suggests that ozonolysis of secondary, oxygenated VOCs is unlikely to yield ambient concentrations of SCI exceeding 104 cm−3 but will contribute strongly to the in situ formation of oxygenated VOCs.

The heterogeneous hydrolysis of dinitrogen pentoxide (N2O5) plays an important role in regulating NOx. The N2O5 uptake coefficient, γ(N2O5), was determined using an iterative box model that was constrained to observational data obtained in suburban Beijing from February to March 2016. The box model determined 2289 individual γ(N2O5) values that varied from

Soot generators are able to produce carbonaceous nanoparticles purposefully and can therefore play a vital role in the calibration of particle instruments with an actual combustion aerosol. Condensation particle counters (CPCs) have become the instrument of choice for legislative measurements of the particle number (PN) concentration. The Euro 5B standard introduced by the European Union in 2011 was the first regulation that introduced a PN limit for the exhaust emission from light duty diesel vehicles. Since then, several other PN regulations for soot-emitting vehicles and combustion engines have been introduced or are currently in draft stages, all with similar requirements for the periodic calibration of the particle counter’s measurement accuracy. It is for this reason that combustion particles produced under laboratory conditions have become an attractive choice of calibration aerosol. Nonetheless, it is often difficult to generate a large amount of particles in the small nanometer range from a laboratory combustion source. In this study, we evaluated the performance of a recently introduced soot generator and its suitability for calibrating the counting efficiency and lower cut-off size of CPCs in the nanometer size range. We first characterized the soot generator’s warm up time to determine when it reaches a stable output when using propane as its fuel. We then investigated the influence of a dozen propane-to-air flow settings on the resulting particle size distribution of the combustion aerosol. Finally, we determined the resulting nanoparticle concentrations for 13 size classes below 20 nm in order to achieve a high size resolution at or near the lower detection limit of common CPCs. We performed our measurements under low-pressure conditions as our group operates CPCs onboard commercial passenger aircraft that are used as an atmospheric measurement platform. Another consideration is that CPCs are also operated elsewhere at much less than standard sea-level pressure. Examples include high-altitude research stations as well as engine test rigs used for vehicle exhaust emission testing or certification operated at elevated locations, e.g., in the USA, Mexico, and China. From these experiments, we concluded that when operating this novel soot generator with 7.5 SLPM airflow and 62.5 SCPM propane flow, it is possible to generate a realistic combustion aerosol for tests and calibrations that is still adequate even in the small nanometer size range. The concentrations measured under these operating conditions were just sufficient for detection with an aerosol electrometer, which is the concentration reference typically used in CPC calibrations.

Langzeitmessungen der atmosphärischen Zusammensetzung sind von zentraler Bedeutung, um die Atmosphärenchemie und den Klimawandel zu verstehen. ACTRIS (Aerosol, Cloud and Trace Gases Research Infrastructure) hat sich zum Ziel gesetzt, ein europaweites Netzwerk von Beobachtungsstationen aufzubauen, die qualitativ hochwertige Daten und Informationen zu kurzlebigen atmosphärischen Bestandteilen liefern und für Nutzer auf der ganzen Welt offen zugänglich machen. Stickstoffmonoxid (NO) und Stickstoffdioxid (NO2), die sogenannten Stickoxide (NOx), spielen eine Schlüsselrolle in der Atmosphärenchemie, da sie zur Bildung von troposphärischem Ozon, Smog und saurem Regen beitragen. Darüber hinaus ist die kurz- und langfristige Exposition mit NO2 mit negativen Auswirkungen auf das menschliche Atmungssystem in Verbindung gebracht worden. Die Hauptquellen von NOx in bewohnten Gebieten sind Verbrennungsprozesse, z.B. von Fahrzeugen und bei industriellen Aktivitäten. NOx-Messungen werden derzeit meist indirekt über Chemilumineszenz-Instrumente durchgeführt, die Korrekturen für Feuchte und Ozon erfordern. Jüngste technologische Fortschritte (z. B. Cavity Attenuated Phase Shift, CAPS, oder Tunable Diode Laser Systeme) erlauben die direkte Detektion von NOx-Komponenten, was Interferenzen vermeidet, die durch die Umwandlung von NO2 in NO hervorgerufen werden. Messvergleiche zeigen aber, dass auch hier neben bekannten Problemen wie Reaktionen in den Einlassleitungen auch unerwartete Artefakte beobachtet werden können. Messvergleiche aber zeigen auch hier, dass neben bekannten Problemen wie Reaktionen in den Einlassleitungen auch unerwartete auftreten können. Um genaue und präzise NOx Messungen mit einer Vielzahl von NOx-Messsystemen in verschiedenen Stationen sicherzustellen, müssen neben der Standardisierung von Messprotokollen und Kalibrierungsverfahren auch an zentraler Stelle durch Messvergleiche und Auditierungen Unterschiede der verschiedenen Messverfahren dokumentiert werden. ACTRIS setzt sich aus central facilities (CFs) und national facilities (NFs) zusammen. Die NFs bilden den explorativen und beobachtenden Teil der Forschungsinfrastruktur. Die CFs sind von grundlegender Bedeutung für die Bereitstellung von harmonisierten und hochpräzisen Daten und stellen eine Vielzahl von Dienstleistungen zur Verfügung. Eines der CFs ist das Reactive Trace Gases In Situ Measurements (CiGas), das für die Überwachung der Datenqualität reaktiver Spurengase verantwortlich ist. Für die Qualitätssicherung (QA) und Qualitätskontrolle (QC) der Stickoxidmessungen an den NFs innerhalb von CiGas ist das Forschungszentrum Jülich (FZJ) zuständig, das auch das World Calibration Center (WCC) für Stickoxide im Global Atmosphere Watch (GAW) Netzwerk beheimatet. Seine Aufgaben umfassen i) die Verbindung von Spurengasmessungen von ACTRIS mit denen anderer Netzwerke, ii) die Beratung und Organisation von Schulungen, iii) die Bereitstellung von Mess- und Auswerteverfahren, iv) das Labelling und die Auditierung von NFs, v) die Implementierung neuer wissenschaftlicher und technologischer Entwicklungen. Es ist vorgesehen, bis 2025 ein zertifiziertes und funktionsfähiges Netzwerk von ACTRIS-Stationen aufzubauen. Es soll der wissenschaftlichen Gemeinschaft qualitativ hochwertige Daten liefern, die die Grundlage für fundierte Entscheidungen der politischen Entscheidungsträger bilden können.

The reactions of biogenic volatile organic compounds (BVOC) with the nitrate radicals (NO

In contrast to summer smog, the contribution of photochemistry to the formation of winter haze in northern mid-to-high latitude is generally assumed to be minor due to reduced solar UV and water vapor concentrations. Our comprehensive observations of atmospheric radicals and relevant parameters during several haze events in winter 2016 Beijing, however, reveal surprisingly high hydroxyl radical oxidation rates up to 15 ppbv/h, which is comparable to the high values reported in summer photochemical smog and is two to three times larger than those determined in previous observations during winter in Birmingham (Heard et al.

Secondary organic aerosol contributes to the atmospheric particle burden with implications for air quality and climate. Biogenic volatile organic compounds such as terpenoids emitted from plants are important secondary organic aerosol precursors with isoprene dominating the emissions of biogenic volatile organic compounds globally. However, the particle mass from isoprene oxidation is generally modest compared to that of other terpenoids. Here we show that isoprene, carbon monoxide and methane can each suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures of atmospheric vapours. We find that isoprene ‘scavenges’ hydroxyl radicals, preventing their reaction with monoterpenes, and the resulting isoprene peroxy radicals scavenge highly oxygenated monoterpene products. These effects reduce the yield of low-volatility products that would otherwise form secondary organic aerosol. Global model calculations indicate that oxidant and product scavenging can operate effectively in the real atmosphere. Thus highly reactive compounds (such as isoprene) that produce a modest amount of aerosol are not necessarily net producers of secondary organic particle mass and their oxidation in mixtures of atmospheric vapours can suppress both particle number and mass of secondary organic aerosol. We suggest that formation mechanisms of secondary organic aerosol in the atmosphere need to be considered more realistically, accounting for mechanistic interactions between the products of oxidizing precursor molecules (as is recognized to be necessary when modelling ozone production). Adding reactive gases such as isoprene to mixtures lowers the production of secondary organic aerosol in the atmosphere, thus reducing the atmospheric particulate burden, with implications for human health and climate.

The oxidation of Δ3 -carene and one of its main oxidation products, caronaldehyde, by the OH radical and O3 was investigated in the atmospheric simulation chamber SAPHIR under atmospheric conditions for NOx mixing ratios below 2 ppbv . Within this study, the rate constants of the reaction of Δ3 -carene with OH and O3 and of the reaction of caronaldehyde with OH were determined to be ( 8.0 ± 0.5 ) × 10 - 11 cm3 s−1 at 304 K , ( 4.4 ± 0.2 ) × 10 - 17 cm3 s−1 at 300 K and ( 4.6 ± 1.6 ) × 10 - 11 cm3 s−1 at 300 K , in agreement with previously published values. The yields of caronaldehyde from the reaction of OH and ozone with Δ3 -carene were determined to be 0.30±0.05 and 0.06±0.02 , respectively. Both values are in reasonably good agreement with reported literature values. An organic nitrate ( RONO2 ) yield from the reaction of NO with RO2 derived from Δ3 -carene of 0.25±0.04 was determined from the analysis of the reactive nitrogen species ( NO y ) in the SAPHIR chamber. The RONO2 yield of the reaction of NO with RO2 derived from the reaction of caronaldehyde with OH was found to be 0.10±0.02 . The organic nitrate yields of Δ3 -carene and caronaldehyde oxidation with OH are reported here for the first time in the gas phase. An OH yield of 0.65±0.10 was determined from the ozonolysis of Δ3 -carene. Calculations of production and destruction rates of the sum of hydroxyl and peroxy radicals ( RO x = OH + HO 2 + RO 2 ) demonstrated that there were no unaccounted production or loss processes of radicals in the oxidation of Δ3 -carene for conditions of the chamber experiments. In an OH -free experiment with added OH scavenger, the photolysis frequency of caronaldehyde was obtained from its photolytical decay. The experimental photolysis frequency was a factor of 7 higher than the value calculated from the measured solar actinic flux density, an absorption cross section from the literature and an assumed effective quantum yield of unity for photodissociation.

Experiments at atmospherically relevant conditions were performed in the simulation chamber SAPHIR, investigating the reaction of isoprene with NO3 and its subsequent oxidation. Due to the production of NO3 from the reaction of NO2 with O3 as well as the formation of OH in subsequent reactions, the reactions of isoprene with O3 and OH were estimated to contribute up to 15% of the total isoprene consumption each in these experiments. The ratio of RO2 to HO2 concentrations was varied by changing the reactant concentrations, which modifies the product distribution from bimolecular reactions of the nitrated RO2. The reaction with HO2 or NO3 was found to be the main bimolecular loss process for the RO2 radicals under all conditions examined.Yields of the first-generation isoprene oxygenated nitrates as well as the sum of methyl vinyl ketone (MVK) and methacrolein (MACR) were determined by high resolution proton mass spectrometry using the Vocus PTR-TOF. The experimental time series of these products are compared to model calculations based on the MCM v3.3.1,1 the isoprene mechanism as published by Wennberg et al.2 and the newly developed FZJ-NO3-isoprene mechanism,3 which incorporates theory-based rate coefficients for a wide range of reactions.Among other changes, the FZJ-NO3-isoprene mechanism contains a novel fast oxidation route through the epoxidation of alkoxy radicals, originating from the formation of nitrated peroxy radicals. This inhibits the formation of MVK and MACR from the NO3-initiated oxidation of isoprene to practically zero, which agrees with the observations from chamber experiments. In addition, the FZJ-NO3-isoprene mechanism increases the level of agreement for the main first-generation oxygenated nitrates. 1 M. E. Jenkin, J. C. Young and A. R. Rickard, The MCM v3.3.1 degradation scheme for isoprene, Atmospheric Chem. Phys., 2015, 15, 11433–11459.2 P. O. Wennberg at al., Gas-Phase Reactions of Isoprene and Its Major Oxidation Products, Chem. Rev., 2018, 118, 3337–3390. 3 L. Vereecken et al., Theoretical and experimental study of peroxy and alkoxy radicals in the NO3-initiated oxidation of isoprene, Phys. Chem. Chem. Phys., submitted.

For the Jülich Atmospheric Chemistry Project campaign (JULIAC) at Forschungszentrum Jülich (FZJ), Germany, the atmospheric simulation chamber SAPHIR was used as a large photochemical flow reactor to study tropospheric chemistry in a rural environment. From an inlet at 50 m height above ground, ambient air was continuously fed through the chamber and exposed to natural solar radiation. A large set of instrumentation allowed for the measurement of NO, NO2, NO3, N2O5, ClNO2, HCHO, HONO, RO2, HO2, OH, kOH, CO, CO2, CH4, H2O, VOCs, aerosols, and O3 in the sampled air. Intensive measurement phases were performed for one month in each season of 2019. One goal of the JULIAC project was to test our understanding of the chemistry of tropospheric ozone formation.To determine the photochemical net ozone production rate in atmospheric air, OX (O3 + NO2) was measured by commercial instruments at the inlet and inside the well mixed chamber. Through careful characterization of the flow reactor it is possible to predict a reference concentration of OX from the inflow measurements which excludes photochemistry. The measured OX concentration in the chamber was compared with the reference. At night, both concentrations agreed, but during daytime the chamber concentration was enhanced due to photochemical OX production. The difference was used to determine diurnal profiles of the net ozone production with 1 hour time resolution. Production rates up to 15 ppbv/h were observed with an accuracy of 1 ppbV/h. Uncertainties in the offsets of the instruments measuring at the inlet and inside the chamber were identified as large contributors (~0.5 ppbV/h) to the overall error. The measured net ozone production rates are compared to production rates that are expected from the reactions of peroxy radicals (HO2, RO2) with NO, all of which were concurrently measured. The analysis includes other chemical reactions that may produce or destroy ozone or NO2 in the lower troposphere.Good agreement (within 10%) between measured and calculated ozone production rates during the spring and summer campaigns confirms that the main contributions to daytime OX production and destruction in the troposphere are overall governed by the reactions of HO2 and RO2 with NO and the reaction of OH radicals with NO2 in the rural environment studied in this project. The presentation will include a discussion of the role of the OH reactivity from VOCs for the local photochemical ozone production.

Due to the potential to fingerprint emissions, carbon stable isotopes are considered a powerful tool to get insight into sources of air pollutants and to study their atmospheric life cycle. Including the independent isotopic knowledge into chemical models, not only concentration but also isotope ratios can be predicted. This provides the possibility to differentiate the impact of source strength from that of chemical reactions in the atmosphere. In a recent study comparing Lagrangian-particle-dispersion-simulations with ambient observations, Betancourt et al. [1] (ACPD2020) found that the observed isotopic age of levoglucosan, a biomass burning tracer, agrees well with the isotopic age derived from back-plumes analyses. This showed that the wintertime aerosol burden from domestic heating observed in residential areas of North-Rheine-Westphalia, Germany, is of local or regional origin. Error analyses though indicated that the largest source of uncertainty was the limited information on emission isotope ratios.In this work, the stable isotope ratios of levoglucosan in aerosol particles emitted from the combustion of 18 different biomass fuels typically used for domestic heating in Western and Eastern Europe (soft and hard woods, brown coals and corn cobs, respectively) were measured by Thermal Desorption- Two-Dimensional Gas Chromatographie- Isotope Ratio Mass Spectrometry (TD-2DGC-IRMS). Additionally to the compound specific measurements, isotopic ratios of total carbon in the fuel parent material, in the precursor cellulose, as well as in sampled aerosol particles were determined.Levoglucosan δ13C was found to vary between -23.6 and -21.7‰ for the C3 plant samples, showing good agreement with Sang et al [2] (EST2012). The brown coal and the C4 plant samples were isotopically heavier, showing isotopic ratios in the range of -21,1 to -18.6‰ and -12.9‰, respectively. In this presentation, the observed levoglucosan δ13C will be discussed with respect to the carbon isotopic composition of the parent materials. The potential of using compound specific δ13C measurements of levoglucosan for improved source apportionment will be addressed.References

The coronavirus-19 (COVID-19) pandemic led to government interventions to limit the spread of the disease that are unprecedented in the last decades. Stay at home orders and other measures led to sudden decreases in atmospheric emissions, most visibly from the transportation sector. We present a review of the current knowledge and understanding of the influence of these emission reductions on atmospheric pollutants concentration and notably air quality with a focus on NO2, PM2.5, and O3 based on more than 200 papers utilizing observations from ground-based and satellite remote sensing instruments. We use the government stringency index as an indicator for the severity of lockdown measures and show how key air pollutants change as the stringency index increases. Changes in NO2 and PM2.5 mass concentration are well-studied globally. The observed decrease of NO2 with increasing stringency index is in general agreement with emission inventories that account for the lockdown. Due to the important influence of atmospheric chemistry on O3 and PM2.5 concentrations, their responses may not be linear with respect to primary pollutants. At most sites, we found O3 increased, whereas PM2.5 decreased slightly, with increasing stringency index. Changes in the PM2.5 composition are found to be understudied and not well-quantified so far. We highlight future research needs for utilizing the emerging data sets covering a full seasonal cycle as a preview of a future state of the atmosphere in a world with targeted permanent reductions of emissions. Finally, we emphasize the need to account for the effects of meteorology, long-term trends, and atmospheric chemistry when determining the lockdown effects on pollutant concentrations, especially on PM2.5.

The chemistry of nitrated alkoxy radicals, and its impact on RO2 measurements using the laser induced fluorescence (LIF) technique, is examined by a combined theoretical and experimental study. Quantum chemical and theoretical kinetic calculations show that the decomposition of β-nitrate-alkoxy radicals is much slower than β-OH-substituted alkoxy radicals, and that the spontaneous fragmentation of the α-nitrate-alkyl radical product to a carbonyl product + NO2 prevents other β-substituents from efficiently reducing the energy barrier. The systematic series of calculations is summarized as an update to the structure–activity relationship (SAR) by Vereecken and Peeters (2009), and shows increasing decomposition rates with higher degrees of substitution, as in the series ethene to 2,3-dimethyl-butene, and dominant H-migration for sufficiently large alkoxy radicals such as those formed from 1-pentene or longer alkenes. The slow decomposition allows other reactions to become competitive, including epoxidation in unsaturated nitrate-alkoxy radicals; the decomposition SAR is likewise updated for β-epoxy substituents. A set of experiments investigating the NO3-initiated oxidation of ethene, propene, cis-2-butene, 2,3-dimethyl-butene, 1-pentene, and trans-2-hexene, were performed in the atmospheric simulation chamber SAPHIR with measurements of HO2 and RO2 radicals performed with a LIF instrument. Comparisons between modelled and measured HO2 radicals in all experiments, performed in excess of carbon monoxide to avoid OH radical chemistry, suggest that the reaction of HO2 with β-nitrate alkylperoxy radicals has a channel forming OH and an alkoxy radical in yields of 15–65%, compatible with earlier literature data on nitrated isoprene and α-pinene radicals. Model concentrations of RO2 radicals when including the results of the theoretical calculations described here, agreed within 10% with the measured RO2 radicals for all species investigated when the alkene oxidation is dominated by NO3 radicals. The formation of NO2 in the decomposition of β-nitrate alkoxy radicals prevents detection of the parent RO2 radical in a LIF instrument, as it relies on formation of HO2. The implications for measurements of RO2 in ambient and experimental conditions, such as for the NO3-dominated chemistry during nighttime, is discussed. The current results appear in disagreement with an earlier indirect experimental study by Yeh et al. on pentadecene.

Emission data of trace gases and aerosols are crucial for atmospheric chemistry models. Since in general emissions cannot be measured directly, they are estimated using various proxy data. Available inventories contain annual values of trace gas and aerosol emissions within given areas, and further split into polluter groups such as road traffic or industry. This separation does not take current meteorological and societal effects into account. Thus, the emission data is known to include possibly large uncertainties.In this work, we develop a system to assess the contribution and their uncertainties of different source categories toe air pollution. As observations of pollutants cannot be directly linked to their source, the four-dimensional variational data assimilation system of the EURopean Air pollution Dispersion – Inverse Model (EURAD-IM) is extended towards a polluter source specific emission correction method. Therefore, the possibility of exploiting different spatial distributions, diurnal cycles, and chemical compositions of the polluter groups is investigated on the model domain of North Rhine-Westfalia, Germany, with 1km x 1km horizontal resolution, where emission by road traffic and industry are the dominant sources for most trace gases and aerosol. As a first approach, we rely on the assumption that pollutants of the same emission sector can be assigned to the same correction factor. From the simulations, separation criteria between different pollution sources are derived as a basis of a decision algorithm applying a random forest method. We found that this system is able to separate emissions between important polluter groups like traffic, industry, and agriculture at least in the cases of high emissions, in well observed areas and during suitable meteorological situations. This means the system performes best when assimilating observations from measurement stations leeward of emission sources and thus integrating sufficient information content to characterize the polluter.

Of the total global annual monoterpene emissions, Δ3-carene contributes 4.5 %, making it the 7th most abundant monoterpene worldwide. As it is primarily emitted by pine trees, Δ3-carene can regionally gain in importance, for example in boreal forests and Mediterranean regions. Oxidation products of monoterpenes such as organic nitrates and aldehydes are known to impact the formation of secondary pollutants such as ozone and particles, so understanding their atmospheric formation and fate is crucial.The photooxidation and ozonolysis of Δ3-carene and the photooxidation and photolysis of its main daytime photooxidation product caronaldehyde were investigated in the atmospheric simulation chamber SAPHIR. Oxidation reactions were studied under atmospheric conditions with high (> 8 ppbv) and low (< 2 ppbv) NOx concentrations. Reaction rate constants of the reaction of Δ3-carene with OH and O3, and of the reaction of caronaldehyde with OH as well as photolysis frequencies of caronaldehyde were determined. Production and destruction rates of the sum of hydroxyl and peroxy radicals (ROx = OH+HO2+RO2) were analysed to determine if there were unaccounted production and loss processes of radicals in the oxidation of Δ3-carene. The yield of Δ3-carene’s oxidation product caronaldehyde was determined from measured timeseries from OH photooxidation and ozonolysis experiments. Additionally, the OH yield from ozonolysis of Δ3-carene was determined.Organic nitrate (RONO2) yields of the reaction of RO2 + NO, from RO2 produced from the reactions of Δ3-carene and caronaldehyde with OH were determined by analyzing the reactive nitrogen species (NOy) in the chamber.

The Jülich Atmospheric Chemistry Project campaign (JULIAC) was performed using the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich (FZJ), Germany. Ambient air was continuously drawn into the chamber through a 50m high inlet line for one month in each season throughout 2019. The residence time of air inside the chamber was one hour. As the sampling point is surrounded by a mixed deciduous forest and is located close to a small–size city (Jülich), the sampled air was influenced by both anthropogenic and biogenic emissions. Measurements included hydroxyl radical (OH) achieved by laser induced fluorescence (LIF) instrument that implemented a newly implemented chemical modulation reactor (CMR) and by differential optical absorption spectroscopy (DOAS). Measurement of both instruments were in good agreement within about 10% and showed no evidence of unknown OH interferences. In addition to OH, hydroxyl and peroxy radicals (HO2 and RO2, respectively), and OH reactivity (kOH, inverse of the OH lifetime) were measured together with a comprehensive set of trace gases concentrations and aerosol properties, allowing for the investigation of the seasonal and diurnal variation of atmospheric oxidant concentrations and their roles in the degradation of volatile organic compounds (VOCs) and contribution to secondary pollutants (ozone and particles).The experimental budget analyses of OH, HO2, RO2, and ROx radical production and destruction rate will be presented for the campaigns in spring and summer (April and August). For most conditions, the concentrations of radicals were sustained by regeneration of HO2 and RO2 radicals via reactions with nitric oxide (NO). The highest radical turnover rates of up to 17 ppbv·hr-1 was observed during a heat wave period in August. For NO levels below 1ppbv, the budget shows a missing OH radical source up to 4 ppbv h-1, while HO2 and RO2 productionand destruction rates were balanced. Above 2 ppbv of NO, missing HO2 production and RO2 loss paths with rates of up to 5 ppbv h-1 were found. In addition, the dataset allows for a detail examination of the importance of radical production and destruction processes from isomerization reactions, HO2 uptake on aerosol, chlorine nitrate chemistry.

Greenhouse gas emissions and air pollution have changed the composition of the atmosphere, and thereby initiated global warming and reduced air quality. Our editorial board members note the need for a deeper understanding of atmospheric fluxes and processes to tackle climate and human health issues.

We report the first-time use of the Lagrangian Particle Dispersion Model (LPDM) FLEXPART to simulate isotope ratios of the biomass burning tracer levoglucosan. Here, we combine the model results with observed levoglucosan concentrations and δ13C to assess the contribution of local vs. remote emissions from firewood domestic heating to the particulate matter sampled during the cold season at two measurements stations of the Environmental Agency of North Rhine-Westphalia, Germany. For the investigated samples, the simulations indicate that the largest part of the sampled aerosol is 1 to 2 days old, and thus originates from local to regional sources. Consequently, photo-chemical aging, also limited by low mean OH concentrations in the cold season, has a minor influence the observed levoglucosan concentration and δ13C. The retro plume ages agree well with those derived from observed δ13C, (the isotopic ages), demonstrating that the limitation of backwards calculations to seven days for this study doesn't introduce any significant bias. A linear regression analysis applied to the experimental levoglucosan δ13C vs. the inverse concentration confirms the young age of aerosol. The high variability in the observed δ13C implies that the local levoglucosan emissions are characterized by very different isotopic ratios in the range of −25.3 to −21.4 ‰. These values are in good agreement with previous studies on levoglucosan source specific isotopic composition in biomass burning aerosol. Comparison between measured and estimated levoglucosan concentrations suggest that emissions are underestimated by a factor of two on average. These findings demonstrate that the aerosol burden from home heating in residential areas is not of remote origin and thus it can be mitigated by reducing local emissions. In this work we show that combining Lagrangian modelling with isotope ratios is valuable to obtain additional insight in source apportionment. Error analysis shows that the largest source of uncertainty is limited information on isotope ratios of levoglucosan emissions. Based on the observed low extent of photochemical processing during cold season, levoglucosan can be used under similar conditions as a conservative tracer without introducing substantial bias.