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Air pollution is one of the grave concerns of the modern era, claiming millions of lives and adversely impacting the economy. Aerosols have been observed to play a significant role in negatively influencing climatological variables and human health in given areas. The current study aimed to study the trend of aerosols and particulates on daily, monthly, seasonal, and annual levels using a 20-year (2002-2021) daily mean aerosol optical depth (AOD) product released by moderate resolution imaging spectrometer (MODIS) sensors for the Hyderabad district in India. The results of the daily mean analysis revealed a rising trend in the number of days with severe AOD (>1), whereas examinations of the seasonal and monthly mean data from 2017 through 2022 showed that peak AOD values alternated between the summer, autumn, and winter seasons over the years. Trend analysis using Mann-Kendall, modified Mann-Kendall, and innovative trend analysis (ITA) tests revealed that AOD increased significantly from 2002 through 2021 (p < 0.05; Z > 0). Furthermore, correlation analysis was performed to check for correlations between AOD levels and certain meteorological factors for the Charminar and Secunderabad regions; it was noticed that temperature had a weak positive correlation with AOD (p < 0.05; r = 0.283 [Secunderabad] - p < 0.05; r = 0.301 [Charminar]), whereas relative humidity developed a very weak negative correlation with AOD (p < 0.05; r = -0.079 [Secunderabad] - p < 0.05; r = -0.109 [Charminar]). [ABSTRACT FROM AUTHOR]

The measurement of carbon dioxide (CO2) has emerged as a cost-effective and straightforward technique for indirectly managing indoor air quality, aiding in the reduction of the potentially pathogen-laden aerosol concentrations to which we are exposed. Unfortunately, inadequate practices often limit the interpretation of CO2 levels and neglect methodologies that ensure proper air renewal. This study presents a novel methodology for measuring and controlling indoor CO2 levels in shared spaces, comprising four stages: analysis, diagnosis, correction protocols, and monitoring/control/surveillance (MCS). This methodology underwent validation in practical settings, including a cultural center (representing spaces with uniform activities) and 40 commercial spaces (with diverse activities) in Zaragoza, Spain. The results indicate the feasibility of swiftly implementing measures to enhance shared air renewal, with the immediate opening of doors and windows being the most direct solution. The proposed methodology is practical and has the potential to mitigate the risk of the aerosol transmission of respiratory diseases. Consequently, we anticipate that this work will contribute to establishing methodological foundations for CO2 measurement as a valuable, standardized, and reliable tool. [ABSTRACT FROM AUTHOR]

Aerosol particles undergo physical and chemical changes during cloud processes. In this work, we quantified the changes in aerosol mixing state using a particle‐resolved model. To this end, we coupled the particle‐resolved aerosol model PartMC‐MOSAIC with the aqueous chemistry module CAPRAM 2.4 and designed cloud parcel simulations that mimicked several cloud cycles that a particle population may be exposed to in polluted urban environments. With ammonium nitrate and ammonium sulfate added to the activated particles, after the cloud evaporated, the activation potential of the resuspended aerosol particles increased for supersaturation thresholds lower than the maximum supersaturation attained in the cloud. Formation of sulfate and nitrate increased the internally mixed state of all particle populations, quantified by the mixing state index χ. The change of aerosol mixing state due to aqueous‐phase chemistry was related to the fraction of activated particles. For a case with low aerosol number concentration, where the activated fraction was up to 60%, χ increased by up to 50 percentage points after cloud processing, reaching an almost completely internal mixture. In contrast, for a case with high aerosol emissions and activated fraction of less than 20%, the increase in χ was less than 20 percentage points, and χ remained below 80% after cloud processing. The change in aerosol mixing state caused by coagulation within the cloud parcel was negligible. These findings highlight the complex influence of cloud processing on particle properties. Plain Language Summary: Every cloud droplet contains at least one aerosol nucleus. The composition and mass of this nucleus can be changed during a cloud's lifetime by several chemical and physical processes. Once the cloud evaporates, a modified aerosol population is released into the atmosphere compared to the population that formed the cloud, which may also have different impacts on climate. In this work, we used a particle‐resolved process model to study the effects of cloud processing on aerosols within clouds. This modeling approach is suitable for this research because each particle is tracked individually, which allows us to quantify changes in particle composition without simplifying assumptions, such as averaging composition within predescribed size ranges. Because of the formation of ammonium sulfate and nitrate in the cloud, particles that formed cloud droplets grew larger and were more likely to form cloud droplets in future cloud cycles. Overall, cloud processing by aqueous‐phase chemistry produced aerosol populations where the particles look more similar to each other in composition. Key Points: Aqueous‐phase chemistry processes cause aerosol populations to be more internally mixedThe change of aerosol mixing state due to aqueous phase chemistry was related to the fraction of activated particlesCoagulation within clouds has a negligible impact on aerosol mixing state [ABSTRACT FROM AUTHOR]

Biomass burning (BB) produces large quantities of carbonaceous aerosol (black carbon and organic aerosol, BC and OA, respectively), which significantly degrade air quality and impact climate. BC absorbs radiation, warming the atmosphere, while OA typically scatters radiation, leading to cooling. However, some OA, termed brown carbon (BrC), also absorbs visible and near UV radiation; although, its properties are not well constrained. We explore three aircraft campaigns from important BB regions with different dominant fuel and fire types (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen [WE‐CAN] in the western United States and ObseRvations of Aerosols above CLouds and their intEractionS and Cloud‐Aerosol‐Radiation Interactions and Forcing for Year downwind of southern Africa) and compare them with simulations from the global chemical transport model, GEOS‐Chem using GFED4s. The model generally captures the observed vertical profiles of carbonaceous BB aerosol concentrations; however, we find that BB BC emissions are underestimated in southern Africa. Our comparisons suggest that BC and/or BrC absorption is substantially higher downwind of Africa than in the western United States and, while the Saleh et al. (2014, https://doi.org/10.1038/ngeo2220) and FIREX parameterizations based on the BC:OA ratio improve model‐observation agreement in some regions, they do not sufficiently differentiate absorption characteristics at short wavelengths. We find that photochemical whitening substantially decreases the burden and direct radiative effect of BrC (annual mean of +0.29 W m−2 without whitening and +0.08 W m−2 with). Our comparisons suggest that whitening is required to explain WE‐CAN observations; however, the importance of whitening for African fires cannot be confirmed. Qualitative comparisons with the OMI UV aerosol index suggest our standard BrC whitening scheme may be too fast over Africa. Plain Language Summary: Smoke from fires has large air quality, health, and climate impacts. However, both the quantity of smoke and its ability to warm or cool the atmosphere remain poorly understood. The two major particle components of smoke (black carbon [BC] and organic aerosol [OA]) interact with incoming solar radiation in distinct ways, with BC generally absorbing light and leading to warming while OA mainly scatters radiation causing cooling. Some types of OA absorb over specific wavelengths of light; these particles are called brown carbon (BrC). Our work uses observations from the western United States and downwind of southern Africa and a global model to better understand the air quality and climate effects of fires in these regions. We find that BC emissions from fires are underestimated in Africa. We find that the black and/or BrC observed downwind of Africa is more absorbing than those in the western United States. We show that our current model does not accurately represent the differing observed absorption strengths for BrC. Comparing the model and observations suggests that BrC loses its ability to absorb (or whitens) in the western United States, but we cannot confirm that over Africa. Key Points: Per model‐measurement analysis, black and brown carbon (BrC) absorption efficiencies are higher in smoke from Africa relative to the western United StatesModeling BrC absorption with black carbon:organic aerosol (BC:OA) parameterizations improves model‐observation agreement without sufficiently distinguishing regionsA universal 1‐day BrC whitening timescale in the model performs better against observations than a scheme based on OH exposure [ABSTRACT FROM AUTHOR]

We introduce a physics‐based aerosol wet removal scheme with unified treatments of aerosol transport and removal by convective clouds into the Community Atmosphere Model version 6. Since several important physical processes are still neglected or poorly represented in this new physics‐based scheme, we develop secondary improvements to the parameterizations of aerosol activation, resuspension, and cloud‐borne aerosol detrainment in this new scheme. Changes in the aerosol wet removal scheme cause tropospheric aerosol concentrations to decrease to different extents: compared to the control run, the physics‐based scheme significantly decreases aerosol burdens by up to 60% over the southern Pacific Ocean, whereas the secondary improvements mitigate the decreasing tendency. The burden changes also depend on aerosol chemical components: the sulfate mass decrease is compensated by secondary production, black carbon (BC) is effectively removed via increasing the hygroscopicity of particulate organic matter from 0 to 0.2, and dust shows the most spatially heterogeneous changes. Simulated aerosol profiles are evaluated against aircraft‐based observations over the Pacific and Atlantic Oceans. The secondary‐improved scheme reduces the overestimations of upper tropospheric BC and sea salt concentrations by a factor of 10 and 1,000, respectively, and reproduces the dependence of BC mass decrease rates on cloud types. Consideration of convective cloud‐borne aerosol detrainment plays the most important role in enhancing the aerosol wet removal and decreasing the positive biases of tropospheric BC and sea salt concentrations. We also summarize unresolved issues related to convective cloud genesis and microphysics, cloud‐borne aerosol evolution, and BC and dust emissions. Key Points: Aerosol wet removal by deep convective clouds significantly impacts global aerosol vertical profilesExplicit convective cloud microphysics in wet removal scheme reduces overestimation of black carbon and sea salt concentrations in upper troposphereParameterization of cloud‐borne (activated) aerosol detrainment from convective clouds to stratiform clouds is an important step in improving the model performance [ABSTRACT FROM AUTHOR]

Entrainment‐mixing process significantly affects cloud micro/macrophysics and the evaluation of aerosol indirect effects. However, it is still an open question as to how to quantify entrainment‐mixing mechanism for broad cloud droplet size distributions (CDSDs). Here, CDSDs with different spectral widths are used to initialize the Explicit Mixing Parcel Model to address this problem, and microphysical properties are compared for different CDSD widths. For relatively broad CDSDs, as the number concentration and liquid water content decrease, the volume‐mean radius and mean radius increase, which is opposite to the scenario for relatively narrow CDSDs and the homogeneous/inhomogeneous conceptual model. For the relatively broad CDSDs, such relationships could be mistaken as inhomogeneous mixing with subsequent ascent in analysis of the conventional microphysical mixing diagram. This then causes traditional homogenous mixing degrees to be unrealistically negative and not applicable for relatively broad CDSDs. New measures are introduced to explicitly account for the effect of CDSD spectral shapes on quantifying entrainment‐mixing mechanism. The new measures yield reasonable ranges of values that conform to the dynamical measures such as the Damköhler and transitional scale numbers, and their temporal variation can be explained physically. This study extends the measures of homogeneous mixing degrees from narrow to broad CDSDs, and sheds new light on the consideration of CDSD shapes in parameterizations of entrainment‐mixing mechanism. Key Points: Microphysical properties and entrainment‐mixing mechanism are dissected for different cloud droplet spectral widthsInhomogeneous mixing with subsequent ascent could be mistakenly identified and traditional measures are not applicable for broad spectraNew measures of homogeneous mixing degrees are introduced and verified [ABSTRACT FROM AUTHOR]

Estimating accurately dust emission flux during aeolian erosion events is crucial for quantifying the amount of dust in the atmosphere. The rare existing field experiments quantifying such flux were mainly performed using the flux‐gradient (FG) method. Here, we present the first intercomparison of the size‐resolved dust fluxes estimated by both the FG and the eddy‐covariance (EC) methods during several erosion events. Both methods were applied simultaneously during the WIND‐O‐V (WIND erOsion in presence of sparse Vegetation)'s 2017 field experiment over an isolated erodible bare plot in South Tunisia. Overall, both methods predict similar dust fluxes for particle smaller than about 4 μm. For coarser particles, the EC method predicts a smaller dust flux than the FG method. Factors explaining this difference are discussed such as the different sampling heads used by the dust particle counters of both methods, or the possible weakening of the constant dust flux layer at the location of the upper dust particle counter of the FG method. This intercomparison highlights the difficulties and advantages of each method as well as their complementarity. Key Points: For the first time, the flux‐gradient method used to estimate size‐resolved dust fluxes is compared to the eddy‐covariance methodBoth methods lead overall to similar dust fluxes. Differences are discussed, highlighting the difficulties and advantages of each methodThe EC method, rarely applied in aeolian soil erosion research, appears promising [ABSTRACT FROM AUTHOR]

We present emission measurements of volatile organic compounds (VOCs) for western U.S. wildland fires made on the NSF/NCAR C‐130 research aircraft during the Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE‐CAN) field campaign in summer 2018. VOCs were measured with complementary instruments onboard the C‐130, including a proton‐transfer‐reaction time‐of‐flight mass spectrometer (PTR‐ToF‐MS) and two gas chromatography (GC)‐based methods. Agreement within combined instrument uncertainties (<60%) was observed for most co‐measured VOCs. GC‐based measurements speciated the isomeric contributions to selected PTR‐ToF‐MS ion masses and generally showed little fire‐to‐fire variation. We report emission ratios (ERs) and emission factors (EFs) for 161 VOCs measured in 31 near‐fire smoke plume transects of 24 specific individual fires sampled in the afternoon when burning conditions are typically most active. Modified combustion efficiency (MCE) ranged from 0.85 to 0.94. The measured campaign‐average total VOC EF was 26.1 ± 6.9 g kg−1, approximately 67% of which is accounted for by oxygenated VOCs. The 10 most abundantly emitted species contributed more than half of the total measured VOC mass. We found that MCE alone explained nearly 70% of the observed variance for total measured VOC emissions (r2 = 0.67) and >50% for 57 individual VOC EFs representing more than half the organic carbon mass. Finally, we found little fire‐to‐fire variability for the mass fraction contributions of individual species to the total measured VOC emissions, suggesting that a single speciation profile can describe VOC emissions for the wildfires in coniferous ecosystems sampled during WE‐CAN. Key Points: A total of 161 measured volatile organic compound emission factors is 26.1 ± 6.9 g kg−1, 67% of which is from oxygenated species76% of the total volatile organic compound emitted mass shows statistically significant dependence on modified combustion efficiencyMass fraction contributions of individual species to the total measured emissions have little variability in 24 western U.S. fires [ABSTRACT FROM AUTHOR]

We analyze new aerosol products from NASA satellite retrievals over the western USA during August 2013, with special attention to locally generated wildfire smoke and downwind plume structures. Aerosol optical depth (AOD) at 550 nm from MODerate Resolution Imaging Spectroradiometer (MODIS) (Terra and Aqua Collections 6 and 6.1) and Visible Infrared Imaging Radiometer Suite (VIIRS) Deep Blue (DB) and MODIS (Terra and Aqua) Multi‐Angle Implementation of Atmospheric Correction (MAIAC) retrievals are evaluated against ground‐based AErosol RObotic NETwork (AERONET) observations. We find a significant improvement in correlation with AERONET and other metrics in the latest DB AOD (MODIS C6.1 r2 = 0.75, VIIRS r2 = 0.79) compared to MODIS C6 (r2 = 0.62). In general, MAIAC (r2 = 0.84) and DB (MODIS C6.1 and VIIRS) present similar statistical evaluation metrics for the western USA and are useful tools to characterize aerosol loading associated with wildfire smoke. We also evaluate three novel NASA MODIS plume injection height (PIH) products, one from MAIAC and two from the Aerosol Single scattering albedo and layer Height Estimation (ASHE) (MODIS and VIIRS) algorithm. Both Terra and Aqua MAIAC PIHs statistically agree with ground‐based and satellite lidar observations near the fire source, as do ASHE, although the latter is sensitive to assumptions about aerosol absorption properties. We introduce a first‐order approximation Smoke Height Boundary Layer Ratio (SHBLR) to qualitatively distinguish between aerosol pollution within the planetary boundary layer and the free troposphere. We summarize the scope, limitations, and suggestions for scientific applications of surface level aerosol concentrations specific to wildfire emissions and smoke plumes using these novel NASA MODIS and VIIRS aerosol products. Key Points: Aerosol optical depth and plume injection height products from new collections of Moderate resolution imaging spectroradiometer and Visible Infrared Imaging Radiometer Suite demonstrate improved capabilities for smoke eventsNew Smoke Height Boundary Layer Ratio indicates when wildfire smoke aerosols are likely to be confined within the planetary boundary layerHeterogeneous vertical aerosol profiles were found downwind of wildfires induced by mountainous terrain and complex boundary layer physics [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosols strongly absorb the solar radiation, affecting the regional and global climate through direct and indirect radiative forcing. The optical properties of BC are critical factors to estimate their radiative forcing. However, the optical absorption of BC is still under controversy partially due to the weakness in quantifying their complex morphology and mixing structures. Although a Discrete Dipole Approximation (DDA) can calculate optical properties of fine particles with arbitrary shapes, an appropriate definition of realistic BC shape models for optical simulation is essentially required. Here we present a novel Electron‐Microscope‐to‐BC‐Simulation (EMBS) tool to construct realistic BC shape models with various morphology and mixing structures for optical calculation using DDA. The optical properties of BC particles with different particle morphology, coating thickness, and embedded fraction (F) are estimated based on electron microscope. We find that absorption enhancement (Eabs) of the realistic irregular model is larger than that of the present commonly used spherical model (i.e., BC aggregate with spherical coating). The BC core morphology greatly influences Eabs of the embedded BC particles with irregular coating when the volume‐equivalent‐diameter ratio of particle to core (Dp/Dc) is larger than 1.8. The F significantly influences Eabs of BC particles, suggesting that the mixing structure between coating and core is an important factor to determine the optical absorption of aged BC particles. The study highlights that the BC core morphology, coating shape, coating thickness, and mixing structures influence their optical properties and should be considered as important variables in climate models. Plain Language Summary: Black carbon (BC) is one of the most important aerosol impacting the regional and global climate change due to its strong optical absorption in the atmosphere. However, it is challenging to precisely estimate the BC optical properties using instruments and numerical models because of its complex morphology and mixing structures in individual particles. This study for the first time presents a novel tool (named as EMBS) to construct realistic 3D shape models based on real BC particles from electron microscopic images for their optical calculation. We found that the commonly used spherical shape models may underestimate the absorption enhancement (Eabs) of BC particles. The mixing structures between BC and non‐BC materials in individual particles can significantly influence their Eabs. The novel EMBS builds a bridge between microscopic observation and BC optical calculation, which has strong implications for reducing the bias of optical calculation and providing important variables in estimating BC climate effects in the future. Key Points: A novel tool is used to construct black carbon (BC) shape models with various morphology and mixing structures based on electron microscopeThe commonly used spherical models may underestimate the absorption enhancement of BC particlesThe embedded fraction and coating shape significantly influence absorption enhancement through determining their mixing structures [ABSTRACT FROM AUTHOR]

Knowledge of hygroscopic properties is essential to prediction of the role of aerosol in cloud formation and lung deposition. Our objective was to introduce a new approach to classify and predict the hygroscopic growth factors (Gfs) of specific atmospheric sub-micrometre particle types in a mixed aerosol based on measurements of the ensemble hygroscopic growth factors and particle number size distribution (PNSD). Based on a non-linear regression model between aerosol source contributions from PMF applied to the PNSD data set and the measured Gf values (at 90% relative humidity) of ambient aerosols, the estimated mean Gf values for secondary inorganic, mixed secondary, nucleation, urban background, fresh, and aged traffic-generated particle classes at a diameter of 110 nm were found to be 1.51, 1.34, 1.12, 1.33, 1.09 and 1.10, respectively. It is found possible to impute (fill) missing HTDMA data sets using a Random Forest regression on PNSD and meteorological conditions. [ABSTRACT FROM AUTHOR]

Activation is the first step in aerosol‐cloud interactions, which have been identified as one of the principal uncertainties in Earth's climate system. Aerosol particles become cloud droplets, or activate, when the ambient saturation ratio exceeds a threshold, which depends on the particle's size and hygroscopicity. In the traditional formulation of the process, only average, uniform saturation ratios are considered. However, turbulent environments like clouds intrinsically have fluctuations around mean values in the scalar fields of temperature and water vapor concentration, which determine the saturation ratio. Through laboratory measurements, we show that these fluctuations are an important parameter that needs to be addressed to fully describe activation. Our results show, even for single‐sized, chemically homogeneous aerosols, that fluctuations blur the correspondence between activation and a particle's size and chemical composition, that turbulence can increase the fraction of aerosol particles which activate, and that the activated fraction decreases monotonically as the concentration of aerosol increases. Taken together, our data demonstrate that fluctuations can have effects equivalent to the aerosol limited and updraft limited regimes, known from adiabatic parcel theory. Plain Language Summary: Formation of cloud droplets occurs when the relative humidity exceeds a threshold value, inducing condensation of water vapor onto preexisting aerosol particles. Which of the preexisting particles become cloud droplets depends on their size and chemical composition. In the conventional view of the process, only the average value of the relative humidity is considered. Our laboratory experiments show that fluctuations, caused by turbulence, must also be considered. These fluctuations can increase the fraction of aerosol particles which become cloud droplets and in general, can mimic the effect of heterogeneity in size and chemical composition of aerosol particles. Key Points: Turbulence blurs the relationship between activation and aerosol size and chemical compositionTurbulence can increase the fraction of aerosol particles that are activatedFor a given supersaturation forcing, activated fraction decreases monotonically as aerosol loading increases [ABSTRACT FROM AUTHOR]

Dry sodium chloride forms cubic crystals, while marine aerosol particles often display more or less irregular deviations from this ideal form. In this study, three non‐ideal cuboidal and octahedral model geometries are investigated. Superellipsoids are tested as a model to simulate the linear backscatter depolarization ratio and the extinction‐to‐backscatter ratio. Gaussian random cubes as well as convex polyhedra are investigated as possible model candidates to quantify the error introduced by simplified model geometries, such as superellipsoids. Uncertainties in the real and imaginary part of the refractive index are studied, and their effect on the optical properties is compared to that caused by morphological variations. Optical calculations were performed at a wavelength of 532 nm using the discrete dipole approximation and the T‐matrix method. The considered size range is representative for marine aerosol generated at low to moderate wind speeds. It is found that cuboidal superellipsoids predict depolarization and extinction‐to‐backscatter ratios that are consistent with observations. On the other hand, octahedral superellipsoids strongly overestimate the depolarization ratio. Gaussian random surface perturbations result in a positive shift of the depolarization ratio compared to cuboidal superellipsoids. By contrast, convex polyhedra yield results that more or less randomly scatter about those of regular cubes. Thus, convex polyhedra are a promising candidate for modeling random errors, while Gaussian random cubes are not. Uncertainties in the refractive index result in perturbations of the depolarization and extinction‐to‐backscatter ratio that are of comparable magnitude as those caused by perturbations of the geometry. Key Points: The depolarization and lidar ratio of dried sea‐salt aerosol are well represented by cuboidal superellipsoids over a representative size rangeConvex polyhedra provide a randomization model suitable for simulating random model errorsModel geometries strongly deviating from cubes, such as octahedra and Gaussian random cubes, overestimate the depolarization ratio [ABSTRACT FROM AUTHOR]

The properties of Southern Ocean (SO) liquid phase non precipitating clouds (hereafter clouds) are examined using shipborne data collected during the Measurements of Aerosols, Radiation and Clouds over the Southern Ocean and the Clouds Aerosols Precipitation Radiation and atmospheric Composition Over the SoutheRN ocean I and II campaigns that took place south of Australia during Autumn 2016 and Summer 2017–2018. Cloud properties are derived using data from W‐band radars, lidars, and microwave radiometers using an optimal estimation algorithm. The SO clouds tended to have larger liquid water paths (LWP, 115 ± 117 g m−2), smaller effective radii (re, 8.7 ± 3 μm), and higher number concentrations (Nd, 90 ± 107 cm−3) than typical values of eastern ocean basin stratocumulus. The clouds demonstrated a tendency for the LWP to increase with Nd presumably due to precipitation suppression up to Nd of approximately 100 cm−3 when mean LWP decreased with increasing Nd. Due to higher optical depth, cloud albedos were less susceptible to changes in Nd compared to subtropical stratocumulus. The highest latitude clouds of the datasets, observed along and near the Antarctic coast, presented a distinctly bimodal character. One mode had the properties of marine clouds further north. The other mode occurred in an aerosol environment characterized by high cloud condensation nuclei concentrations and elevated sulfate aerosol without obvious continental aerosol markers. These regions of higher cloud condensation nuclei tended to have higher Nd, smaller re and higher LWP suggesting sensitivity of cloud properties to seasonal biogenic aerosol production in the high latitude SO. Key Points: The properties of liquid Southern Ocean (SO) clouds vary with latitudeSO low clouds are susceptible to aerosol concentrationsSO clouds near Antarctica have high droplet numbers compared to lower latitude SO clouds [ABSTRACT FROM AUTHOR]

For a given cloud, whether the cloud top is predominately made up of ice crystals or supercooled liquid droplets plays a large role in the clouds overall radiative effects. This study uses collocated airborne radar, lidar, and thermodynamic data from 12 high‐altitude flight legs during the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) to characterize Southern Ocean (SO) cold sector cloud top phase (i.e., within 96 m of top) as a function of cloud top temperature (CTT). A training data set was developed to create probabilistic phase classifications based on High Spectral Resolution Lidar data and Cloud Radar data. These classifications were then used to identify dominant cloud top phase. Case studies are presented illustrating examples of supercooled liquid water at cloud top at different CTT ranges over the SO (−3°C < CTTs < −28°C). During SOCRATES, 67.4% of sampled cloud top had CTTs less than 0°C. Of the subfreezing cloud tops sampled, 91.7% had supercooled liquid water present in the top 96 m and 74.9% were classified entirely as liquid‐bearing. Liquid‐bearing cloud tops were found at CTTs as cold as −30°C. Horizontal cloud extent was also determined as a function of median cloud top height. Plain Language Summary: Low‐level clouds over the Southern Ocean have a large effect on the region's radiation budget. The radiation budget is strongly influenced by the phase (liquid or ice) of cloud tops, which is where most solar radiation is reflected, and most infrared radiation is radiated to space. For this reason, identifying the phase of cloud tops is important. In this study, airborne radar, lidar, and temperature data from 12 high‐altitude flight legs during the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) are used to characterize Southern Ocean cloud top phase as a function of cloud top temperature. The results show that liquid is the dominant phase present in clouds over the Southern Ocean, with liquid present at cloud top temperatures as cold as −30°C. Key Points: Airborne radar, lidar, and thermodynamic data are used to determine Southern Ocean cloud top phase as a function of cloud top temperatureConsidering only clouds with subfreezing cloud top temperatures, the dominant phase at cloud top in 74.9% of clouds was liquidLiquid‐bearing cloud tops were even found at temperatures as cold as −30°C [ABSTRACT FROM AUTHOR]

A numerical investigation was conducted to assess the possible impact of desert dust and urban aerosols on a very intense and deadly thunderstorm that occurred within the Tel Aviv metropolitan area on 4 January 2020. For these purposes, the cloud drop nucleation scheme within the spectral (bin) microphysics scheme (SBM) in the Weather Research and Forecasting Model (WRF) was coupled with the GoCart (desert) dust model and with hourly surface observations of urban aerosols. Using SBM integrated mass contents and simulated vertical velocities, the dynamic lightning scheme was able to forecast lightning rates within thunderclouds developing in an environment of marine or marine/continental aerosols with dust and/or urban aerosol forcings. Of these aerosol forcings (or factors), the urban aerosols (pollution) intensified lightning rates in convective clouds forming at and just off the Israeli coastline (referred to as the Urban Aerosol Lightning Enhancement Effect; ULE). The inclusion of continental aerosols with dust and urban aerosol sources resulted in the simulation exhibiting the most intense lightning and precipitation storm (referred to as Large Aerosol Small Aerosol Invigoration Effect; LASI). Yet, a comparison of model results and observations suggests that it was the combination of desert dust and urban aerosols alone that focused storm development over western Tel Aviv. The result was that high lightning rates initially focused over western Tel Aviv were accompanied by and then succeeded by a period of heavy rain that led to deadly flooding. Plain Language Summary: The possible role of urban pollution on lightning and rainfall was investigated using a sophisticated cloud model embedded in a weather forecast model. The cloud model takes into account the impact of different sources of dust, including desert dust on cloud formation, and intensification into thunderstorm producing clouds. The day chosen for study was a day with lots of lightning and even deadly flooding in the city of Tel Aviv, Israel. The results showed that urban pollution intensifies lightning rates and precipitation amounts over the city. When large raindrops produced on large dust particles interacted with small drops produced from urban pollution, intense lightning and rainfall was forecast to occur in the area of deadly flooding. Hence, to forecast the intensity and location of severe storms, forecasts should take into account different sources of dust and pollution. Key Points: Urban pollution intensifies lightning ratesUrban aerosol and desert dust combined to cause flooding and deadly rainsThe forecast position of deadly thunderstorms was very sensitive to aerosol type and concentration [ABSTRACT FROM AUTHOR]

We implement an existing aerosol module named Spectral Radiation Transport Model for Aerosol Species (SPRINTARS) in the Chinese Academy of Sciences Flexible Global Ocean–Atmosphere–Land System (CAS‐FGOALS) model and simulate the global aerosol properties over 2002–2014. The simulated surface mass concentrations of individual aerosols generally reproduce the observed ones. The simulated spatial‐temporal distributions of the aerosol optical depths (AODs) are evaluated with multisource satellite retrievals, and the simulated AOD, Ångström Exponent (AE), and single scattering albedo (SSA) are further evaluated with the ground‐based Aerosol Robotic Network (AERONET) measurements. The spatial distribution of the modeled AOD is found to be generally comparable to the satellite retrievals. The interannual and seasonal variations of the modeled AOD over various aerosol regimes are also overall consistent with the AERONET observations. With respect to the AE, our model can reproduce the interannual variations fairly well over the dust dominant regions, and generally capture the seasonal variations over the industrial domain regions. Over the industrial domain regions, however, the systematic underestimation of the simulated AE is found, which is in part due to the biases of wind fields and overestimation of the relative humidity (RH) by the host model. With respect to the SSA, our model can also generally reproduce the observed seasonal variations, while the modeled values are typically lower than the observations, especially over North Africa. Key Points: The interannual and seasonal variation of modeled aerosol optical properties are overall consistent with the observations at most regionsBiases of the meteorological fields are responsible for underestimation of the Ångström Exponent over the industrial dominant regionsThe seasonal variations of aerosol optical depth in the dust dominant region can be better reproduced with more realistic wind fields [ABSTRACT FROM AUTHOR]

Measurement‐model comparisons for various atmospheric species have been widely used for evaluating the reliability of model simulations, yet such comparisons are quite limited for atmospheric isoprene due to the lack of systematic observations over a large scale. Here, we collected ambient air samples concurrently at 20 sites in China during 2012–2014 and compared the observed isoprene mixing ratios with those simulated by coupling MEGAN v2.1 with the 3‐D Regional chEmical trAnsport Model. The observed average isoprene concentration for all 1,731 samples is 0.35 ± 0.03 ppbv, 13% higher than the model simulated average of 0.31 ± 0.02 ppbv; while during the growing season, the simulated average (0.53 ± 0.05 ppbv) is almost the same as the observed average (0.52 ± 0.04 ppbv). The observed isoprene average level in the north (0.35 ppbv) is similar to that in the south (0.37 ppbv). However, the model simulated average in the south (0.53 ppbv) is ∼4 times that in the north (0.14 ppbv). The model overestimated the observations at most southern sites but underestimated at most northern sites in the growing season, which might be resulted from inadequate characterization of isoprene‐emitting land vegetation with fast afforestation in the north and rapid urbanization in the south. Compared to the model simulation, the observations revealed abnormally high isoprene levels in winter at some northern sites, largely due to nonbiogenic emissions, as evidenced by the enhancements of measured combustion tracers concurrent with the abnormally elevated isoprene levels. Plain Language Summary: Isoprene alone accounts for approximately one‐third of global emission of volatile organic compounds from both nature and human activities, yet in many parts of the world biogenic isoprene emission estimates have large uncertainties (reported isoprene emission estimates span 4–29 TgC y−1 in China), and narrowing these uncertainties is a challenging task. Here we collected ambient air samples concurrently at 20 sites over China during 2012–2014, and made measurement‐model comparison to check the emission estimates for isoprene, and found that although overall observed and predicted average isoprene levels matched well particularly during growing seasons, there exists a south‐north discrepancy that model simulated averages in the south were much higher than the north while their observed averages were quite near each other. Modeled values overestimated at most southern sites but underestimated at most northern sites, probably the fast afforestation in the north and rapid urbanization in the southeast were inadequately characterized in the model. Abnormally higher isoprene levels were observed in winter at some northern sites probably due to contribution from nonbiogenic sources. Our results highlight that high‐resolution PFT/LAI, field campaigns with higher spatial and temporal resolutions, as well as biomass burning activity data, are necessary for better observation‐model comparison. Key Points: Ambient isoprene mixing ratios observed at 20 sites across China during 2012–2014 are compared with the MEGAN‐REAM model simulationThe model simulated averages in the south were much higher than those in north, while the observed averages were much more similarAbnormally high isoprene levels were observed in winter at some northern sites probably due to contributions from nonbiogenic sources [ABSTRACT FROM AUTHOR]

Mineral dust emitted from the arid regions of the Arabian Peninsula (AP), in particular Kingdom of Saudi Arabia (KSA), is an important contributor to the northern hemispheric aerosol loading. Dust events over AP are frequent and persistent throughout the year, with a peak in occurrence and intensity between March and August. This study examines the variability of dust events that occurred over AP during 2003–2017 using long‐term dust optical depth retrieved from MODIS satellite measurements. Dust profiles were derived from CALIOP satellite measurements to assess the vertical distributions of the dust events. Our analysis suggests that the formation of extreme dust events is primarily associated with strong high‐pressure systems that occur over AP. Northerly Shamal winds transport dust aerosols from surrounding arid regions to the AP, amplifying the dust aerosol loading across the country. CALIOP dust profiles show that the dust aerosols reach up to 4 km height above sea level, with peak concentrations at an altitude around 1.5 km. Dry deposition of dust is the dominant removal process over the Arabian Gulf, and wet deposition of dust is the dominant removal process over the Red Sea. A total of 49 extreme dust events occurred during the period between 2003 and 2017, over a combined total of 207 days. We observe a significant increase in the frequency of dust events between 2007 and 2012, peaking in 2012, followed by a marked decrease in the following years. We attribute this sudden decline in dust activity after 2012 to enhanced winter rainfall, after noticing increased soil moisture and vegetation coverage during the dust seasons that followed wetter winters. A strengthened Red Sea trough in the middle and the upper altitudes produced favorable conditions for strong moisture convergence and increased rainfall over AP, which may have dampened dust activity during 2013–2017. Key Points: Dust optical properties extracted from MODIS and CALIOPFormation stages and trends of extreme dust events discussedRecent decline in the dust events explained [ABSTRACT FROM AUTHOR]

East Asia features frequent dust storms and intensive anthropogenic emissions. The mixing of natural dust and anthropogenic pollutants exerts complicated impacts on air pollution and regional climate. Studies have focused on chemical interactions of the mixed pollution, while the meteorological feedback and influences on atmospheric chemistry have not been fully investigated. Here, a comprehensive study on a widespread dust storm and its influence on the air quality downwind was conducted by combining multiple observations and modeling. We found that dust originated from Gobi Desert was mixed with anthropogenic pollutants after transported to the Yangtze River Delta (YRD). Through scattering and absorbing radiation, dust aerosol perturbed solar energy budget and led to a more stabilized planetary boundary layer (PBL). A reduction of 15% in PBL height (184 m) weakened the dispersion of locally emitted pollutants and increased primary pollution by 10% in YRD city clusters. Besides, the mixed plume over offshore areas warmed the entire lower atmosphere and increased surface evaporation. Accordingly, ozone formation was accelerated by ∼1 ppbv/h within PBL under higher temperature, and secondary aerosol was increased due to faster photochemical and heterogeneous oxidation. Such enhancements substantially contributed to air quality deterioration in YRD region. This work reveals the complexity of interactions between natural dust and anthropogenic pollutants through both atmospheric chemistry and meteorological feedbacks, which is of great importance in both regional air pollution and climate. Key Points: Natural dust mixed with anthropogenic aerosols exerted great interactions with radiation and meteorologyDust‐induced aerosol‐radiation interactions over land enhanced the pollution accumulationFormation of ozone and secondary aerosols over ocean was promoted by aerosol‐radiation interactions [ABSTRACT FROM AUTHOR]

Aerosols modify cloud microphysical and radiative properties and thus impact the shortwave and long‐wave cloud forcing (LWCF). This study first reports the finding of contrasting aerosol effects on LWCF in South East Asia and Amazon in the Community Atmosphere Model version 5.3 (CAM5.3), which corresponds to the sum of LW indirect and semi‐direct effects investigated in Ghan et al. (2012, http://doi.org/10.1175/jcli-d-11-00650.1). A series of numerical experiments are conducted to decompose the complex aerosol effects on LWCF. Our analysis indicates that the cooling (negative aerosol effects on LWCF) in Amazon is due mainly to the aerosol effects on warm clouds and the inhibition of vertical motion by the aerosol‐induced radiative cooling. In contrast, the warming (positive aerosol effects on LWCF) in South East Asia is due mainly to the aerosol effect on homogeneous freezing, thus, reducing the ice particle size and prolonging the existence of ice cloud. Our results emphasize that a comprehensive analysis of integrated aerosol effects on both warm and ice clouds is necessary for better understanding the aerosol effects on LWCF. Plain Language Summary: Aerosol particles in the atmosphere modify the number and size of cloud droplets and ice particles, and impact the cloud top height and extension, which modulate the thermal energy absorbed and emitted by clouds. We carried out a series of global climate model experiments and found that an increasing number of aerosol particles result in opposite effects in two regions. A cooling effect in Amazon is due to the enhanced number and reduced size of water cloud droplets. The shielding effect of water cloud cools the surface, thus, makes the cloud hardly develop higher. On the other hand, the warming effect in South East Asia is due mainly to the reduced ice particle size, prolonging the existence of the ice cloud. Our results indicate that the integrated aerosol effects on both water and ice clouds are complex, yet significant in understanding their impacts on cloud and energy in the atmosphere. Key Points: Contrasting aerosol effects on long‐wave cloud forcing in South East Asia (warming) and in Amazon (cooling) are identifiedThe contrasting long‐wave effects are related to different aerosol effects on cloud microphysics, thermodynamics, and radiationA comprehensive analysis of integrated aerosol effects on clouds is necessary for estimating and understanding the long‐wave effect [ABSTRACT FROM AUTHOR]

Iceland contributes 30–40 million tons of mineral dust to the atmosphere each year. Emission events are linked to exceedingly high concentrations of PM10, poor air quality, and respiratory disease, particularly in Reykjavík. Volcaniclastic aerosols have unique microphysical properties, and usually are porous and highly angular, with large surface areas bearing ultrafine, nanoscale dustcoats. The large internal void space contributes to low particle density, believed to affect emission and deposition rates in the atmospheric boundary layer, as well as the range of transport. However, the aerodynamic and sedimentological factors that govern dust entrainment in these high‐latitude settings are not well constrained empirically, providing little guidance for the parameterization of aerosol dispersion models. A series of laboratory wind tunnel simulations were carried out under full climate control to evaluate these effects for Icelandic samples collected from five active dust sources, inclusive of volcanic ash and glaciofluvial sediments. PM10 emission rates measured in this study are similar in magnitude to those obtained in a small number of field studies within selected high‐latitude regions, and for volcanic ash using a PI‐SWERL. The scaling with friction velocity is well described by the 1988 dust emission model of Gillette and Passi, while the parameterization appears to be strongly dependent on the median particle size. Sediments from the coarsest Icelandic dust sources were found to be most emissive, owing to the importance of particle impact, while the proportionate amount of PM10 within the test bed was not found to correlate with the emission rate. Key Points: Volcaniclastic sediments with high median diameter are most emissive, with emission rates comparable to most erodible soilsThe quantity of PM10 within the Icelandic sediment is not a good indicator of the relative magnitude of the aerosol emission rateGlaciogenic sediments associated with subglacial outburst floods are more emissive than finer sample of 2010 Eyjafjallajökull ash [ABSTRACT FROM AUTHOR]

Since the emergence of the global contemporary graffiti and street art, urban spaces have become filled with a variety of techniques and art pieces, whether as a beautification method, commemorative and community art, or even activism. Ecology has also been a small part of this, with growing concern over our environment's health (as well as our own), disappearing living species and habitats, and trying to imagine a better, less destructive humankind (see: Arrieta, 2014). But, how can this art - based mostly on aerosol spray cans and thus not very eco-friendly - in urban spaces contribute to ecological awareness? Do nature, animal and plant motifs pave a way towards understanding the environment, or simply serve as aesthetic statements? This paper will examine these questions with the example of Belgrade, Serbia, and several local (but also global) practices. This text is based on ongoing research as part of Street Art Walks Belgrade project (STAW BLGRD) and interviews with a group of artists. [ABSTRACT FROM AUTHOR]

Climate science and nuclear weapons testing have a long and surprisingly intimate relationship. The global networks that monitored the Fukushima radiation plume and forecasted its movement are the direct descendants of systems and computer models developed to trace fallout from weapons tests. Tracing radioactive carbon as it cycles through the atmosphere, the oceans, and the biosphere has been crucial to understanding anthropogenic climate change. The earliest global climate models relied on numerical methods very similar to those developed by nuclear weapons designers for solving the fluid dynamics equations needed to analyze shock waves produced in nuclear explosions. The climatic consequences of nuclear war also represent a major historical intersection between climate science and nuclear affairs. Without the work done by nuclear weapons designers and testers, scientists would know much less than they now do about the atmosphere. In particular, this research has contributed enormously to knowledge about both carbon dioxide, which raises Earth’s temperature, and aerosols, which lower it. Without climate models, scientists and political leaders would not have understood the full extent of nuclear weapons’ power to annihilate not only human beings, but other species as well. In the post-Cold War era, US national laboratories built to create the most fearsome arsenal in history are now using their powerful supercomputers, their expertise in modeling, and their skills in managing very large data sets to address the threat of catastrophic climate change. [ABSTRACT FROM PUBLISHER]

Climate models generally simulate a unidirectional, positive liquid water path (LWP) response to increasing aerosol number concentration. However, satellite observations and large‐eddy simulations show that the LWP may either increase or decrease with increasing aerosol concentration, influencing the overall magnitude of the aerosol indirect effect (AIE). We use large‐eddy simulation to investigate the LWP response of a marine stratocumulus cloud and its dependence on different parameterizations for obtaining cloud droplet number concentration (CDNC). The simulations confirm that the LWP response is not always positive—regardless of CDNC treatment. However, the AIE simulated with the model version with prescribed CDNC is almost 3 times larger compared to the version with prognostic CDNC. The reason is that the CDNC in the prognostic scheme varies in time due to supersaturation fluctuations, collection, and other microphysical processes. A substantial spread in simulated AIE may thus arise simply due to the CDNC treatment. Plain Language Summary: Our poor understanding of aerosol‐cloud‐radiation interactions (aerosol indirect effects) results in a major uncertainty in estimates of anthropogenic aerosol forcing. In climate models, the cloud water response to an increased aerosol number concentration may be especially uncertain as models simplify, or do not account for, processes that affect the cloud droplet number concentration and the total amount of cloud water. In this study, we employ large‐eddy simulation to explore how different model descriptions for obtaining the number concentration of cloud droplets influences the cloud water response of a marine stratocumulus cloud and thus the simulated aerosol indirect effect. Our simulations show a qualitatively similar cloud water response regardless of model description: the total amount of cloud water increases first and then decreases with increasing aerosol concentration. However, the simulated aerosol indirect effect is almost 3 times as large when the number concentration of cloud droplets is prescribed compared to when it is dependent on the calculated supersaturation and other microphysical processes such as collisions between cloud droplets. Our findings show that a relatively simple difference in the treatment of the number concentration of cloud droplets in climate models may result in a significant spread in the simulated aerosol indirect effect. Key Points: We use large‐eddy simulation to investigate the response of a marine stratocumulus cloud to increasing aerosol concentrationThe aerosol indirect effect is almost 3 times as large when the cloud droplet concentration is prescribed instead of prognosticTime variations in supersaturation and collection influence the overall cloud droplet number and aerosol indirect effect [ABSTRACT FROM AUTHOR]

The local aerosol emission effect is investigated by comparing two numerical simulations (1982–2016) with the U.K. HadGEM3‐GA6 model nudged to the same ERA‐Interim circulation. One includes full historical Coupled Model Intercomparison Project Phase 5 RCP4.5 aerosol emission changes while the second uses a monthly aerosol climatology from 1982. At global scale, the emission scenario does not change the mean surface energy balance, but it shows strong regional contrasts. Thus, we focus on regions where the change in emission has been the largest: North America, Europe, India, and China. No clear impact on temperature trends is found over China although aerosol emissions have increased in recent decades. This could be explained by a stronger role of meteorology in this region rather than direct surface heating, and also by a more limited change in aerosol optical depth compared to regions such as Europe. Other regions show clearer responses to aerosol effect, consistent with previous studies: cooler maximum temperatures (with historical emission compared to fixed emissions) where emissions have increased (North‐East of India) and warmer maximum temperatures where emissions have decreased (Europe). However, in each region, the interannual variability in temperatures is strongly controlled by the circulation. Precipitation is also locally decreased (0.5 mm/day) over North India during summer due to a reduction of moisture convergence in the boundary layer (where no nudging is applied). Based on these simulations, we suggest that radiation‐driven aerosol emission impacts on local surface temperature and precipitation are not linear and can be mitigated or cancelled by the local dynamics. Key Points: Nudged simulation (1982–2016) is used to force the model dynamics and isolate the effect of aerosol emissions from the circulation feedbackThe effect of aerosol emissions on temperatures over China is weak, possibly due to lower AOD changes and overshadowed by meteorologyOther regions have more consistent response between radiation and temperatures; the effect on precipitation is however very limited [ABSTRACT FROM AUTHOR]

We investigated the characteristics of charged aerosols produced by high-voltage power lines (HVPLs) to explore the effects on respiratory disease incidence among those who handle HVPLs. Charged aerosol currents and charged aerosol concentrations were measured over 24 h at 12 sites. Aerosol current effective levels were 2.7 times higher compared to exposed and control sites. This pattern of relative enhancement at exposed sites was seen consistently in all measurements and the difference was 1.7 higher at exposed sites. Correlation analysis among all important variables revealed strong positive correlations between currents and concentration, currents and magnetic field, humidity and concentration, and humidity and particles of 10 µm or less (PM10), while negative correlations were observed between charged aerosol concentrations and wind velocity and between wind velocity and humidity. Estimated production of charged aerosols from HVPLs found that people who work with HVPLs are highly likely to be exposed to charged aerosols. [ABSTRACT FROM AUTHOR]

Fog poses a severe environmental problem in the North China Plain, China, which has been witnessing increases in anthropogenic emission since the early 1980s. This work first uses the WRF/Chem model coupled with the local anthropogenic emissions to simulate and evaluate a severe fog event occurring in North China Plain. Comparison of the simulations against observations shows that WRF/Chem well reproduces the general features of temporal evolution of PM2.5 mass concentration, fog spatial distribution, visibility, and vertical profiles of temperature, water vapor content, and relative humidity in the planetary boundary layer throughout the whole period of the fog event. Sensitivity studies are then performed with five different levels of anthropogenic emission as model inputs to systematically examine the comprehensive impacts of aerosols on fog microphysical, macrophysical, radiative, and dynamical properties. The results show that as aerosol concentration increases, fog droplet number concentration and liquid water content all increase nonlinearly; but effective radius decreases. Macrophysical properties (fog fraction, fog duration, fog height, and liquid water path) also increase nonlinearly with increasing aerosol concentration, with rates of changes smaller than microphysical properties. Further analysis reveals distinct aerosol effects on thermodynamic and dynamical conditions during different stages of fog evolution: increasing aerosols invigorate fog formation and development by enhancing longwave‐induced instability, fog droplet condensation accompanying latent heat release, and thus turbulence, but delay fog dissipation by reducing surface solar radiation, surface sensible, and latent heat fluxes, and thus suppressing turbulence during the dissipation stage. Key Points: Aerosols strengthen and prolong fog events in polluted environmentAerosol effects are stronger on microphysical properties than macrophysical propertiesTurbulence is enhanced by aerosols during fog formation and growth but suppressed during fog dissipation [ABSTRACT FROM AUTHOR]

The paper provides an overview of an airborne measurement campaign with a microlight aircraft over the Pokhara Valley region, Nepal, a metropolitan region in the central Himalayan foothills. This is the first aerial measurement in the central Himalayan foothill region, one of the polluted but relatively poorly sampled regions of the world. Conducted in two phases (in May 2016 and December 2016–January 2017), the goal of the overall campaign was to quantify the vertical distribution of aerosols over a polluted mountain valley in the Himalayan foothills, as well as to investigate the extent of regional transport of emissions into the Himalayas. This paper summarizes results from the first phase where test flights were conducted in May 2016 (pre-monsoon), with the objective of demonstrating the potential of airborne measurements in the region using a portable instrument package (size with housing case: 0.45 m × 0.25 m × 0.25 m, 15 kg) onboard an ultralight aircraft (IKARUS-C42). A total of five sampling test flights were conducted (each lasting for 1–1.5 h) in the Pokhara Valley to characterize vertical profiles of aerosol properties such as aerosol number and size distribution (0.3–2 µ m), total particle concentration (>14 nm), aerosol absorption (370–950 nm), black carbon (BC), and meteorological variables. Although some interesting observations were made during the test flight, the study is limited to a few days (and only a few hours of flight in total) and thus the analysis presented may not represent the entire pollution–meteorology interaction found in the Pokhara Valley. The vertical profiles of aerosol species showed decreasing concentrations with altitude (815 to 4500 m a.s.l.); a steep concentration gradient below 2000 m a.s.l. in the morning; and mixed profiles (up to ca. 4000 m a.s.l.) in the afternoon. The near-surface (<1000 m a.s.l.) BC concentrations observed in the Pokhara Valley were much lower than pre-monsoon BC concentrations in the Kathmandu Valley, and similar in range to Indo-Gangetic Plain (IGP) sites such as Kanpur in India. The sampling test flight also detected an elevated polluted aerosol layer (around 3000 m a.s.l.) over the Pokhara Valley, which could be associated with the regional transport. The total aerosol and black carbon concentration in the polluted layer was comparable with the near-surface values. The elevated polluted layer was also characterized by a high aerosol extinction coefficient (at 550 nm) and was identified as smoke and a polluted dust layer. The observed shift in the westerlies (at 20–30 ∘ N) entering Nepal during the test flight period could be an important factor for the presence of elevated polluted layers in the Pokhara Valley. [ABSTRACT FROM AUTHOR]

An accurate simulation of the absorption properties is key for assessing the radiative effects of aerosol on meteorology and climate. The representation of how chemical species are mixed inside the particles (the mixing state) is one of the major uncertainty factors in the assessment of these effects. Here we compare aerosol optical properties simulations over Europe and North America, coordinated in the framework of the third phase of the Air Quality Model Evaluation International Initiative (AQMEII), to 1 year of AERONET sunphotometer retrievals, in an attempt to identify a mixing state representation that better reproduces the observed single scattering albedo and its spectral variation. We use a single post-processing tool (FlexAOD) to derive aerosol optical properties from simulated aerosol speciation profiles, and focus on the absorption enhancement of black carbon when it is internally mixed with more scattering material, discarding from the analysis scenes dominated by dust. We found that the single scattering albedo at 440 nm (ω0,440) is on average overestimated (underestimated) by 3–5 % when external (core-shell internal) mixing of particles is assumed, a bias comparable in magnitude with the typical variability of the quantity. The (unphysical) homogeneous internal mixing assumption underestimates ω0,440 by ∼14 %. The combination of external and core-shell configurations (partial internal mixing), parameterized using a simplified function of air mass aging, reduces the ω0,440 bias to -1/-3 %. The black carbon absorption enhancement (Eabs) in core-shell with respect to the externally mixed state is in the range 1.8–2.5, which is above the currently most accepted upper limit of ∼1.5. The partial internal mixing reduces Eabs to values more consistent with this limit. However, the spectral dependence of the absorption is not well reproduced, and the absorption Ångström exponent AAE 675440 is overestimated by 70–120 %. Further testing against more comprehensive campaign data, including a full characterization of the aerosol profile in terms of chemical speciation, mixing state, and related optical properties, would help in putting a better constraint on these calculations. [ABSTRACT FROM AUTHOR]

Ship traffic is a major source of aerosol particles, particularly near shipping lanes and harbours. In order to estimate the contribution to exposure downwind of a shipping lane, it is important to be able to measure the ship emission contribution at various distances from the source. We report on measurements of atmospheric particles, 7-20 km downwind of a shipping lane in the Baltic Sea Sulphur Emission Control Area (SECA) at a coastal location in southern Sweden during a winter and a summer campaign. Each ship plume was linked to individual ship passages using a novel method based on wind field data and Automatic ship Identification System data (AIS), where varying wind speeds and directions were applied to calculate a plume trajectory. In a situation where AIS data is not matching measured plumes well or if AIS data is missing, we provide an alternative method with particle number concentration data. The shipping lane contribution to the particle number concentration in Falsterbo was estimated by subtracting background concentrations from the ship plume concentrations, and more than 150 plumes were analysed. We have also extrapolated the contribution to seasonal averages and provide recommendations for future similar measurements. Averaged over a season, the contribution to particle number concentration was about 18% during the winter and 10% during the summer, including those periods with wind directions when the shipping lane was not affecting the station. The corresponding contribution to equivalent black carbon was 1.4%. [ABSTRACT FROM AUTHOR]

This article presents a description and a comparative study of the optical and microphysical properties of aerosols measured above Cluj-Napoca city in Romania and above Koforidua city in Ghana. Atmospheric aerosols have a major impact on climate and our health. We analyzed the Aerosol Optical Thickness at 440 nm (AOT), the Ångström parameter (a 440 - 870 nm), the fine and coarse volume concentrations and the single scattering albedo, in order to describe the aerosol properties at these 2 stations. We used daily averages which are calculated for every day when the available number of measurements is higher than 3. At CLUJ_UBB station, the Aerosol Optical Thickness at 440 nm wavelength has values between 0.031 and 0.699, with an average of 0.229 ± 0.11. At Koforidua_ANUC station, the AOT440 has values between 0.106 and 2.580, with an average of 0.742 ± 0.50, much higher than the values measured at CLUJ_UBB. The aerosol at the two locations has different properties, at Cluj-Napoca the urban industrial type is predominant while at Koforidua the predominant type is mineral dust. [ABSTRACT FROM AUTHOR]

Abstract We discuss 15 years (2000–2015) of daily-integrated PM 2.5 samples from the Cape Grim Station. Ion beam analysis and positive matrix factorisation are used to identify six source-type fingerprints: fresh sea salt (57%); secondary sulfate (14%); smoke (13%); aged sea salt (12%); soil dust (2.4%); and industrial metals (1.5%). An existing hourly radon-only baseline selection technique is modified for use with the daily-integrated observations. Results were not significantly different for days on which >20 hours were below the baseline radon threshold compared with days when all 24 hours satisfied the baseline criteria. This relaxed daily baseline criteria increased the number of samples for analysis by almost a factor of two. Two radon baseline thresholds were tested: historic (100 mBq m−3), and revised (50 mBq m−3). Median aerosol concentrations were similar for both radon thresholds, but maximum values were higher for the 100 mBq m−3 threshold. Back trajectories indicated more interaction with southern Australia and the Antarctic coastline for air masses selected with the 100 mBq m−3 threshold. Radon-only baseline selection using the 50 mBq m−3 threshold was more selective of minimal terrestrial influence than a similar recent study using wind direction and back trajectories. The ratio of concentrations between terrestrial and baseline days for the primary sources soil, smoke and industrial metals was 3.4, 2.6, and 5.5, respectively. Seasonal cycles of soil dust had a summer maximum and winter minimum. Seasonal cycles of smoke were of similar amplitude for terrestrial and baseline events, but of completely different shape: peaking in autumn and spring for terrestrial events, compared to summer for baseline conditions. Seasonal cycles of industrial metals had a summer maximum and winter minimum. A significant fraction of the Cape Grim baseline smoke and industrial metal contributions appeared to be derived from long-term transport (>3 weeks since last terrestrial influence). Graphical abstract Image 1 Highlights • Radon-222 only technique developed for baseline air masses identification. • Technique was applied on 24-hr PM 2.5 observations at Cape Grim. • Baseline days needed air masses with 20 h or more above Radon-222 threshold. • Non-baseline concentrations of soil and smoke were 3.4 and 2.6 times higher. Hourly Radon-222 measurements can determine the minimum number of hours needed under baseline conditions in order to classify daily 24-hr PM 2.5 concentrations. [ABSTRACT FROM AUTHOR]

This reply addresses a comment questioning one of the lines of evidence I used in a 2015 study (S15) to argue for a less negative aerosol radiative forcing. The comment raises four points of criticism. Two of these have been raised and addressed elsewhere; here I additionally show that even if they have merit the S15 lower bound remains substantially (0.5 W m–2) less negative than that given in the AR5. Regarding the two other points of criticism, one appears to be based on a poor understanding of the nature of S15's argument; the other rests on speculation as to the nature of the uncertainty in historical SO2 estimates. In the spirit of finding possible flaws with the top-down constraints from S15, I instead hypothesize that an interesting—albeit unlikely—way S15 could be wrong is by inappropriately discounting the contribution of biomass burning to radiative forcing through aerosol–cloud interactions. This hypothesis is interesting as it opens the door for a role for the anthropogenic (biomass) aerosol in causing the Little Ice Age and again raises the specter of greater warming from ongoing reductions in SO2 emissions. [ABSTRACT FROM AUTHOR]

The author comments on the effects of aerosol radiative forcing on the environment and climate. The topics discussed include the correlation of radiative forcing and global warming, the status of aerosol forcing in the Northern Hemisphere (NH), and the reasons why the NH is warmer compared to other areas.

Outdoor traffic‐related airborne particles can infiltrate a building and adversely affect the indoor air quality. Limited information is available on the effectiveness of high efficiency particulate air (HEPA) filtration of traffic‐related particles. Here, we investigated the effectiveness of portable HEPA air cleaners in reducing indoor concentrations of traffic‐related and other aerosols, including black carbon (BC), PM2.5, ultraviolet absorbing particulate matter (UVPM) (a marker of tobacco smoke), and fungal spores. This intervention study consisted of a placebo‐controlled cross‐over design, in which a HEPA cleaner and a placebo "dummy" were placed in homes for 4‐weeks each, with 48‐hour air sampling conducted prior to and during the end of each treatment period. The concentrations measured for BC, PM2.5, UVPM, and fungal spores were significantly reduced following HEPA filtration, but not following the dummy period. The indoor fraction of BC/PM2.5 was significantly reduced due to the HEPA cleaner, indicating that black carbon was particularly impacted by HEPA filtration. This study demonstrates that HEPA air purification can result in a significant reduction of traffic‐related and other aerosols in diverse residential settings. [ABSTRACT FROM AUTHOR]

The article presents research designed to calculate the historical aerosol effective radiative forcing (ERF) in the HadGEM3‐GA7 climate model. The authors offer their evaluation regarding the suitability of this model for inclusion in the UK Earth system model, UKESM1.

Black carbon (BC) aerosols in the atmosphere strongly affect radiative forcing. They are mainly removed from the air by wet deposition, and their lifetime is controlled by their water uptake ability or hygroscopicity, which is a function of aerosol mixing states. It is well known that atmospheric aging processes coat various materials on BC aerosols and affect their mixing states and hygroscopicity. However, detailed relations between the aging processes and the hygroscopicity and mixing state of BC aerosol particles in polluted city areas are not well understood. Here, we studied the temporal variation in hygroscopicity and its correlation with the mixing state of ambient BC particles during the summer of 2017 in Shanghai, China, using a hygroscopic tandem differential mobility analyzer inline with a singleparticle soot photometer (HTDMA--SP2 system) as well as a single-particle aerosol mass spectrometer (SPAMS). BC particles with 120, 240, and 360 nm in dry diameter were humidified at relative humidity (RH) D85 %. After humidification, particles with growth factors (GFs) of 1.0, 1.2, and 1.4, representing the BC particles with different hygroscopicities (hydrophobic, transition, and hydrophilic modes, respectively), were analyzed with a SP2 to obtain their BC mixing states. The diurnal trends in coating thickness and chemical mixing state show that coating materials of BC particles were distinct between daytime and nighttime. The differences were associated with the hygroscopicity of BC particles. Singleparticle mass spectrometry and other chemical characterization techniques revealed that with lower temperature and higher RH during nighttime, formation or condensation of nitrates resulted in an enhanced hygroscopicity of BC particles. During daytime, secondary organic carbon formation was mainly responsible for the change of hygroscopicity of BC particles. Due to the high hygroscopicity of inorganic nitrate, a thinner nitrate coating on BC particles could convert fresh BC particles to aged hygroscopic ones during nighttime while a thicker coating layer of secondary materials was required to reach the same overall hygroscopicity during daytime because of the participation of secondary organic carbon. Different atmospheric aging processes between daytime and nighttime led to the change of BC particles' mixing states, which play a fundamental role in determining their hygroscopicity. To our knowledge, this is the first report of links between temporal variations in the hygroscopic growth of BC particles and atmospheric aging processes in polluted environments. These findings have significant ramifications in understanding the aging process, wet removal, and climate effects of BC particles. [ABSTRACT FROM AUTHOR]

Black carbon (BC) emissions from open biomass burning (BB) are known to have a considerable impact on the radiative budget of the atmosphere at both global and regional scales; however, these emissions are poorly constrained in models by atmospheric observations, especially in remote regions. Here, we investigate the feasibility of constraining BC emissions from BB using satellite observations of the aerosol absorption optical depth (AAOD) and the aerosol extinction optical depth (AOD) retrieved from OMI (Ozone Monitoring Instrument) and MODIS (Moderate Resolution Imaging Spectroradiometer) measurements, respectively. We consider the case of Siberian BB BC emissions, which have the strong potential to impact the Arctic climate system. Using aerosol remote sensing data collected at Siberian sites of the AErosol RObotic NETwork (AERONET) along with the results of the fourth Fire Lab at Missoula Experiment (FLAME-4), we establish an empirical parameterization relating the ratio of the elemental carbon (EC) and organic carbon (OC) contents in BB aerosol to the ratio of AAOD and AOD at the wavelengths of the satellite observations. Applying this parameterization to the BC and OC column amounts simulated using the CHIMERE chemistry transport model, we optimize the parameters of the BB emission model based on MODIS measurements of the fire radiative power (FRP); we then obtain top-down optimized estimates of the total monthly BB BC amounts emitted from intense Siberian fires that occurred from May to September 2012. The top-down estimates are compared to the corresponding values obtained using the Global Fire Emissions Database (GFED4) and the Fire Emission Inventory--northern Eurasia (FEI-NE). Our simulations using the optimized BB aerosol emissions are verified against AAOD and AOD data that were withheld from the estimation procedure. The simulations are further evaluated against in situ EC and OC measurements at the Zotino Tall Tower Observatory (ZOTTO) and also against aircraft aerosol measurement data collected in the framework of the Airborne Extensive Regional Observations in SIBeria (YAK-AEROSIB) experiments. We conclude that our BC and OC emission estimates, considered with their confidence intervals, are consistent with the ensemble of the measurement data analyzed in this study. Siberian fires are found to emit 0.41 ± 0.14 Tg of BC over the whole 5-month period considered; this estimate is a factor of 2 larger and a factor of 1.5 smaller than the corresponding estimates based on the GFED4 (0.20 Tg) and FEI-NE (0.61 Tg) data, respectively. Our estimates of monthly BC emissions are also found to be larger than the BC amounts calculated using the GFED4 data and smaller than those calculated using the FEI-NE data for any of the 5 months. Particularly large positive differences of our monthly BC emission estimates with respect to the GFED4 data are found in May and September. This finding indicates that the GFED4 database is likely to strongly underestimate BC emissions from agricultural burns and grass fires in Siberia. All of these differences have important implications for climate change in the Arctic, as it is found that about a quarter of the huge BB BC mass emitted in Siberia during the fire season of 2012 was transported across the polar circle into the Arctic. Overall, the results of our analysis indicate that a combination of the available satellite observations of AAOD and AOD can provide the necessary constraints on BB BC emissions. [ABSTRACT FROM AUTHOR]

The article examines the effectiveness of sequential aerosol technique (SAT) against riverine tsetse flies in southern Africa. An overview on the tuning control operations concerning the reproduction of tsetse flies, is highlighted. Also emphasized are the tsetse species' challenging habitats in the adaptation of SAT, is also emphasized.

Background Dental care professionals are exposed to aerosols from the oral cavity of patients containing several pathogenic microorganisms. Bioaerosols generated during dental treatment are a potential hazard to dental staff, and there have been growing concerns about their role in transmission of various airborne infections and about reducing the risk of contamination. Aims To investigate qualitatively and quantitatively the bacterial and fungal aerosols before and during clinical sessions in two dental offices compared with controls. Methods An extra-oral evacuator system was used to measure bacterial and fungal aerosols. Macroscopic and microscopic analysis of bacterial species and fungal strains was performed and strains of bacteria and fungi were identified based on their metabolic properties using biochemical tests. Results Thirty-three bioaerosol samples were obtained. Quantitative and qualitative evaluation showed that during treatment, there is a significant increase in airborne concentration of bacteria and fungi. The microflora included mainly gram-positive organisms (Staphylococcus epidermidis and Micrococcus spp.), gram-positive rod-shaped bacteria and those creating endospores as well as non-porous bacteria and mould fungi (Cladosporium and Penicillium). Conclusions Exposure to the microorganisms identified is not a significant occupational hazard for dental care professionals; however, evidence-based prevention measures are recommended. [ABSTRACT FROM AUTHOR]

The fact that aerosols are important players in Earth's radiation balance is well accepted by the scientific community. Several studies have shown the importance of characterizing aerosols in order to constrain surface radiative fluxes and temperature in climate runs. In numerical weather prediction, however, there has not been definite proof that interactive aerosol schemes are needed to improve the forecast. Climatologies are instead used that allow for computational efficiency and reasonable accuracy. At the monthly to subseasonal range, it is still worth investigating whether aerosol variability could afford some predictability, considering that it is likely that persisting aerosol biases might manifest themselves more over time scales of weeks to months and create a nonnegligible forcing. This paper explores this hypothesis using the ECMWF's Ensemble Prediction System for subseasonal prediction with interactive prognostic aerosols. Four experiments are conducted with the aim of comparing the monthly prediction by the default system, which uses aerosol climatologies, with the prediction using radiatively interactive aerosols. Only the direct aerosol effect is considered. Twelve years of reforecasts with 50 ensemble members are analyzed on the monthly scale. Results indicate that the interactive aerosols have the capability of improving the subseasonal prediction at the monthly scales for the spring/summer season. It is hypothesized that this is due to the aerosol variability connected to the different phases of the Madden–Julian oscillation, particularly that of dust and carbonaceous aerosols. The degree of improvement depends crucially on the aerosol initialization. More work is required to fully assess the potential of interactive aerosols to increase predictability at the subseasonal scales. [ABSTRACT FROM AUTHOR]

The Angouran Mine, located in northwest Iran, is the largest Zn-Pb producer in the Middle East. This study was designed to investigate the distribution, geochemistry, and mineralogy of the aerosols in the mining area and to assess their likely health impacts on the local residents. For this purpose, 36 aerosol samples were collected from 2014 to 2015 at nine sites located in mine district and upwind and downwind directions. The concentration of potentially toxic elements in the aerosols was determined using AAS instrument. Size, morphology, and mineralogy of the particles were studied using SEM and EDX spectra. The results indicate that the amount of total suspended particles in upwind, mine district, and downwind sites is 95.5, 463.4 and 287.5 µg/m3, respectively. The concentrations of PM2.5 in the three locations are 8.9, 134.7, and 51.8 µg/m3, whereas the PM10 contents are 2.9, 74.4, and 15.5 µg/m3, respectively. These observations point to the impact of mining activities on the concentration of aerosols in the local atmosphere. The values of air quality index also show the probable effects of the mining activities on the health of the local populations, especially for allergic peoples. The average concentration of Zn in the samples collected from the mining district (290 µg/kg) is much higher than its value in the upwind sites (27 µg/kg). The highest concentration of As (70 µg/kg), Cd (10 µg/kg), and Pb (3 µg/kg) is in downwind sites, which shows the negative impact of mining activities on the local air quality. Temporally, the highest concentration of the studied elements is recorded in spring season, especially for PM2.5 collected in downwind stations. Based on the results of SEM and EDX spectra, three groups of minerals, i.e., carbonates, silicates, and sulfides, are present in the aerosol particles, confirming the local source for the aerosols. SEM analyses showed that the aerosol particles with dissimilar chemical composition have different morphologies such as irregular, rounded, elongated, and angular. On the basis of the results, the mining activities in the Angouran Zn-Pb Mine may have various short- and long-term consequences on the public health, especially due to high amount of the finer particles (PM2.5) and the higher concentration of the potentially toxic elements in PM2.5 which can penetrate into the lungs. [ABSTRACT FROM AUTHOR]

Atmospheric aerosols can significantly affect the Earth’s radiative balance due to absorption, scattering and aerosol-cloud interactions. Although our understanding of aerosol properties has improved over recent decades, aerosol radiative forcing remains as one of the largest uncertainties when attributing recent and projecting future anthropogenic climate change. Ensembles of a coupled ocean-atmosphere general circulation model were used to investigate how the representation of aerosols within the model can affect climate. The control simulation consisted of a 30-year simulation with an interactive aerosol scheme and aerosol emissions that evolve from 1980-2009. The sensitivity tests included using constant 1980 emissions, using prescribed 2-D monthly mean AODs, modifying the aerosol vertical distribution, altering aerosol optical properties, and changing the parameters used for calculating the aerosol first indirect effect. The results of these sensitivity studies show how modifying certain aspects of the aerosol scheme can significantly affect radiative flux and temperature. In particular, it was shown that compared to the control simulation the use of constant 1980 aerosol emissions decreased the average winter surface temperature of the Arctic by 0.2 K and that the use of prescribed 2-D monthly mean AODs reduced the annual global surface temperature by 0.3 K. Increasing the vertical distribution of anthropogenic aerosols in the model and altering aerosol optical properties modified localised radiative fluxes and temperatures, but the most significant change in global surface temperature (1.3 K) was caused by removing sea salt and organic matter from the calculation of cloud droplet number concentration. [ABSTRACT FROM AUTHOR]

Dust aerosol plays an important role in the Earth System. As a natural aerosol, dust aerosol is often calculated interactively in global climate models and temporal variations of dust emission in the past century are far less constrained compared to those of anthropogenic aerosol emissions. Here we evaluate dust emission in East Asia simulated by 15 climate models participating in the Coupled Model Intercomparison Project Phase 5. The results show that none of the models can reproduce the observed decline of dust event frequency during 1961–2005 over East Asia. The models tend to simulate either much less decline or even increase of dust emission. The discrepancy is mainly ascribed to weaker or opposite trends of surface wind speeds and precipitation in the models. These results cast a doubt on the interpretation of long‐term variations of dust‐affected fields in climate models and highlight the need for further improvements of the models. Plain Language Summary: Atmospheric aerosol is one of key factors that influence climate change. Aerosols include anthropogenic aerosols (such as sulfate aerosol and black carbon from fossil fuel burning) and natural aerosols (such as dust that is emitted by strong winds over bare soil). Climate models are important tools we use to predict the climate in the future, and the reliability of climate models lies in their ability to reproduce the change of climate system in the past. Here we examine the ability of climate models in reproducing the long‐term change of dust storm frequency in East Asia. First, historical records of dust events show the dust activities decreased greatly during 1961 to 2005 over East Asia. Compared to this observation, current climate models are unable to reproduce the large decline of dust activities during 1961 to 2005. The reason is that climate models cannot capture the decrease of surface wind speed and increase of precipitation. These results imply that climate models may not represent well the change of meteorological elements (e.g., temperature and clouds) that will be affected by dust. Our results highlight urgent need to improve the performance of climate models in simulating long‐term dust change. Key Points: CMIP5 models show similar dust source regions in East Asia but differ substantially in the boundaries of these regionsCMIP5 models cannot reproduce the observed large decline of dust events in East Asia during 1961‐2005CMIP5 models simulate either smaller or opposite trends of surface wind speeds and precipitation, which lead to the discrepancy in dust [ABSTRACT FROM AUTHOR]

Abstract: The spaceborne Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument provides valuable information on the vertical distribution of global aerosol and is often used to evaluate vertical aerosol distributions in general circulation models (GCMs). Here we show, however, that the detection limit of the CALIOP retrievals mean background aerosol is not detected, leading to substantially skewed statistics that moreover differ significantly by product. In the CALIOP Level 2 product this missing low‐backscatter aerosol results in the retrieved aerosol distribution significantly overrepresenting aerosol backscatter and extinction in the middle and upper troposphere if taken to be representative of the undetected aerosol. The CALIOP Level 3 product assumes no aerosol where none is detected, which then leads to an underestimation in the aerosol extinction profile in the upper troposphere. Using the ECHAM‐HAM GCM, we estimate that the mean fraction of aerosol undetected by CALIOP daytime (nighttime) retrievals is 41% (44%) globally. [ABSTRACT FROM AUTHOR]

Nucleation and growth of aerosol particles from atmospheric vapors constitutes a major source of global cloud condensation nuclei (CCN). The fraction of newly formed particles that reaches CCN sizes is highly sensitive to particle growth rates, especially for particle sizes <10 nm, where coagulation losses to larger aerosol particles are greatest. Recent results show that some oxidation products from biogenic volatile organic compounds are major contributors to particle formation and initial growth. However, whether oxidized organics contribute to particle growth over the broad span of tropospheric temperatures remains an open question, and quantitative mass balance for organic growth has yet to be demonstrated at any temperature. Here, in experiments performed under atmospheric conditions in the Cosmics Leaving Outdoor Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN), we show that rapid growth of organic particles occurs over the range from -25 °C to 25 °C. The lower extent of autoxidation at reduced temperatures is compensated by the decreased volatility of all oxidized molecules. This is confirmed by particle-phase composition measurements, showing enhanced uptake of relatively less oxygenated products at cold temperatures. We can reproduce the measured growth rates using an aerosol growth model based entirely on the experimentally measured gas-phase spectra of oxidized organic molecules obtained from two complementary mass spectrometers. We show that the growth rates are sensitive to particle curvature, explaining widespread atmospheric observations that particle growth rates increase in the singledigit-nanometer size range. Our results demonstrate that organic vapors can contribute to particle growth over a wide range of tropospheric temperatures from molecular cluster sizes onward. [ABSTRACT FROM AUTHOR]