Aerosols in the atmosphere have significant health and climate impacts. Organic aerosol (OA) accounts for a large fraction of the total aerosol burden, but models have historically struggled to accurately simulate it. This study compares two very different OA model schemes and evaluates them against a suite of globally distributed airborne measurements with the goal of providing insight into the strengths and weaknesses of each approach across different environments.

This study gives an overview of acid deposition from the Model Inter-Comparison Study for Asia (MICS-Asia) phase III. Wet deposition simulated by a total of nine models is evaluated with observation data from the Acid Deposition Monitoring Network in East Asia (EANET). The total deposition maps comparing to emissions over Asia are presented. To seek a way to improve the model performance, ensemble approaches and the precipitation-adjusted method are discussed.

We have determined the rate coefficient and mechanism for the reaction of the OH radical with methane sulphonamide, a trace gas which has recently been found in the atmosphere. The rate coefficient is 1.4 × 10⁻¹³ cm³ molec.⁻¹ s⁻¹, which indicates a tropospheric lifetime of > 2 months. The observation of CO, CO₂, SO₂, HNO₃, HCOOH, and N₂O products enabled us to derive a detailed reaction mechanism for the reaction, which proceeds predominantly by H abstraction from the CH₃ group.

We found significant seasonal variations in optical and chemical properties of organic aerosols in the urban region and changes in photo-resistivity of light-absorbing organic aerosols (e.g., brown carbon) owing to the high UV radiation in the atmosphere. Our results suggest that photochemical degradation plays a significant role in light-absorbing organic aerosol abundances and might be an important removal mechanism of light-absorbing aerosols in the atmosphere.

Synchronous online monitoring was performed in two urban sites and three rural sites in Henan Province. Results show that PM_2.5 was more acidic in urban aerosols than that in rural regions, and excess NH_x concentrations played a key role in the local particle pH values. Air masses transported from rural and agricultural regions may promote the sulfate formation in urban aerosols. Therefore, ammonia should be involved in the regional strategy for improving the air quality in China.

Using a high-resolution model we simulate the transition from night to day clouds on southern West Africa using observations from the DACCIWA project. We find that the radiative effects of clouds help mantain a thick cloud layer in the night, while the mixing of cloud air with air above during the day, aided by moisture and heat fluxes at the surface, thins this layer and promotes its transition to other clouds. The effect of changing wind with height accelerates the transition.

Ambient air pollution is a major cause of premature death in China. We examine the street-scale variation of pollutant levels in Beijing using air pollution dispersion and chemistry model ADMS-Urban. Campaign measurements are compared with simulated pollutant levels, providing a valuable means of evaluating the impact of key processes on urban air quality. Air quality modelling at such fine scales is essential for human exposure studies and for informing choices on future emission controls.

Our results highlight the contribution of gasoline-direct-injection (GDI) vehicles to aerosols, both primary and secondary. The major particles from GDI vehicles are organic and soot particles; they actively participate in chemical conversions in the atmosphere, leading to morphology and composition changes in hours. Rapid ageing could be attributable to the acid-catalysed mechanism and high concentrations of gaseous pollutants. These results would be beneficial for control of PM_2.5 pollution.

MAX-DOAS tropospheric NO₂ vertical column retrievals from a set of European measurement stations are compared to regional air quality models which contribute to the operational Copernicus Atmosphere Monitoring Service (CAMS). Correlations are on the order of 35 %–75 %; large differences occur for individual pollution plumes. The results demonstrate that future model development needs to concentrate on improving representation of diurnal cycles and associated temporal scalings.

In this paper, using dispersion modelling with emission inventories it was determined that on average 45 % of the total CO pollution that affects Beijing is transported from other areas. About half of the CO comes from beyond the immediate surrounding areas. Finally three classification types of pollution were identified and used to analyse the APHH winter campaign. The results can inform targeted control measures to be implemented in Beijing and the other regions to tackle air quality problems.

Simulated diurnal PM_2.5 with WRF-Chem is primarily controlled by planetary boundary layer (PBL) mixing and emission variations. Modeling bias is likely primarily due to inefficient PBL mixing of primary PM_2.5 during the night. The increase in PBL mixing strength during the night can significantly reduce biases. This study underscores that more effort is needed to improve the boundary mixing processes of pollutants in models with observations of PBL structure and mixing fluxes besides PBL height.

Dust optical properties are necessary to quantify aerosol radiative effects and to retrieve their properties. This study reveals the importance of the dust refractive index (RI) for the model development of its optical properties. Our results indicate that the scattering matrix elements of different dust particles can be reasonably reproduced by choosing appropriate RIs but a fixed particle geometry, and the RI influences the scattering matrix elements differently from geometric factors.

We characterized aerosol composition and sources near two steel plants in a coastal region in fall and spring seasons. Our results showed substantially different aerosol composition and sources between the two seasons. We observed significant impacts of steel plant emissions on aerosol chemistry nearby, and we found that aerosol particles emitted from the steel plants were dominated by ammonium sulfate/bisulfate; NO_x/CO and NO_x/SO₂ were distinct from those in the absence of industrial plumes.

In this paper, we analyze a climate simulation over Germany of a continuous period in May and June 2016, with resolutions of 600 m, 300 m, and 150 m. This resolution is high enough that strong convective rain events like rain showers and thunderstorms are sufficiently resolved. Our analysis shows that the tendency of convection to organize is improved at higher resolution and that the highest-resolution simulation is closest to weather radar data.

Benzene and polycyclic aromatic compounds are toxic air pollutants and ubiquitous in the environment. Using a chemical transport model, we have determined the net impact of vehicle emissions on ambient concentrations of these species. Traffic emissions were found to be a significant fraction of ambient pollution in the densely populated modelled region of North America. Our simulations demonstrate the air quality benefits that would result from transitioning to a zero-emission vehicle fleet.

The Kathmandu Valley experiences high levels of air pollution. In this study, atmospheric gases and particulate matter were characterized by online and off-line measurements, with an emphasis on understanding their sources. The major sources of particulate matter and trace gases were identified as garbage burning, biomass burning, and vehicles. The majority of secondary organic aerosol was attributed to anthropogenic precursors, while a minority was attributed to biogenic gases.

Many general circulation models (GCMs) have difficulty simulating Arctic clouds and climate, causing substantial inter-model spread. By analyzing various model simulation results, we found that the association between the enhanced poleward transports of heat and moisture and an increase in liquid clouds over the Arctic is evident in GCMs. Our study demonstrates that enhanced poleward heat and moisture transport in a model can improve simulations of Arctic clouds and climate.

This paper seeks to better our understanding of how dust storms are represented in a weather model. Depending on how well the model can represent the storm, it can change the dust forecast significantly. This is important for predictions of air quality and visibility; as dust can heat and cool the air in its environment, it is also crucial for calculating the Earth's energy budget. Here, we communicate the uncertainty in a dust model and the effect that it may have on dust forecasts.

Organic aerosols have been shown to exist often in a semi-solid or amorphous, glassy state. Highly viscous particles behave differently than their well-mixed liquid analogues with consequences for a variety of aerosol processes. Here, we introduce a new predictive mixture viscosity model called AIOMFAC-VISC. It enables us to predict the viscosity of aqueous organic mixtures as a function of temperature and chemical composition, covering the full range of liquid, semi-solid, and glassy states.

We use three Earth system models to estimate the impact of regional air pollutant emissions reductions on global and regional surface temperature. We find that removing human-caused air pollutant emissions from certain world regions (such as the USA) results in warming of up to 0.15 °C. We use our model output to calculate simple climate metrics that will allow for regional-scale climate impact estimates without the use of computationally demanding computer models.

We find that extensive biomass burning aerosol plumes from southern Africa can profoundly influence clouds in the southeastern Atlantic. Concurrent variations in vertical velocity, however, are found to magnify the relationship between boundary layer aerosol and the cloud droplet number. Neglecting these covariances may strongly bias the sign and magnitude of aerosol impacts on the cloud droplet number.

In this work, we show that the previously identified strong spatiotemporal correlation relationship between the low-level cloud amount (LCA) and its large-scale environmental proxy, the estimated low-level cloud fraction (ELF), holds for various low-level cloud types over the globe rather than for a specific cloud type. However, we also identify several weaknesses of the ELF and suggest a potential pathway to further improve it in the future as a global proxy for LCA.

Methanethiol (MeSH) is a reduced sulfur gas originating from phytoplankton, with a global ocean source of ~ 17 % of dimethyl sulfide (DMS). It has been little studied and is rarely observed over the ocean. In this work, MeSH was measured at much higher levels than previously observed (3–36 % of parallel DMS mixing ratios). MeSH could be a significant source of atmospheric sulfur over productive regions of the ocean, but its distribution, and its atmospheric impact, requires more investigation.

There has been a growing interest in reducing emissions of soot particles to slow global warming and improve air quality. However, estimating the effect of reduced emissions is complex, as soot particles absorb solar radiation and influence heating rates, clouds, and humidity and can influence climate far outside their emission region. Here we investigate the impact of soot emitted in four major emissions areas, using different emissions rates, to see whether location and magnitude matter.

Our laboratory experiments show that the rate coefficient for the termolecular reaction between OH and NO₂ is enhanced in the presence of water vapour. Using a chemistry transport model we show that our new parameterization of the temperature, pressure, and bath-gas dependence of this reaction has a significant impact on, for example, NO_x and the HNO₂ / NO₂ ratio when compared to present recommendations.

In this study, we analyzed air concentration data on SO₄^2-, NO₃^-, NH₄⁺, HNO₃, and SO₂ measured by CASTNET in the US and by CAPMoN in Canada to reveal the temporal and spatial trends of air pollutants over the eastern US and Eastern Canada. We also explained (1) why the reductions of SO₂ were faster than SO₄^2- and (2) why NO₃^- did not decrease during the cold season except in the Midwest and southern Ontario despite NO_x emissions being significantly reduced for the whole region.

Extensive measurements of the aerosol and cloud condensation nuclei (CCN) properties in South Asian outflow to the northern Indian Ocean were carried out as a part of the ICARB-2018 experiment during winter. At high supersaturations, most of the aerosols in the South Asian outflow become activated as CCN, whereas the aerosol system over the equatorial Indian Ocean is less CCN efficient even at higher supersaturations.

Atmospheric aerosols are solid or liquid particles suspended in the air. They are known as a health risk, but they also influence the Earth's climate. The composition of aerosols becomes important when predicting their effect on climate. We show both seasonal and year-to-year variability of aerosol chemical composition in the boreal forest of Finland. We observed a consistent bimodal seasonal trend: a biogenic summertime maximum and an anthropogenic wintertime maximum in the mass concentration.

Atmospheric dust interacts with solar radiation, which influences the climate, with larger-sized particles having a heating effect, and smaller-sized particles having a cooling effect. Previous studies on long-range dust transport have found larger particles than expected, without a model to explain their transport. We find that sufficient electrostatic forces suspend more larger particles in the atmosphere and may help explain unexpected large particle transport.

We studied the trend of US ozone pollution from 1990 to 2015 using EPA observations and computer simulations. Observations indicated a decrease in peak ozone at noon due to regulations and a slight increase in ozone in early morning and late afternoon possibly. Our modeling system confirmed these findings and provided detailed information about ozone photochemistry. These results revealed the success of previous control measures and provide scientific evidence for the future regulations.

Pore condensation and freezing (PCF) is an ice nucleation mechanism explaining ice formation at low ice supersaturation. It is assumed that liquid water condenses in pores of solid aerosol particles below water saturation followed by ice nucleation within the pores. This study discusses conditions of pore filling, homogeneous ice nucleation within the volume of porewater, and growth of ice out of the pores, taking the effect of negative pressure within pores below water saturation into account.

We developed a novel tracer-based approach to optimize the organic carbon (OC) to levoglucosan ratio for estimating the precise concentration of OC emitted from biomass burning (OC_BB). Application of this ratio indicates that 68 % (winter) and 63 % (spring) of OC originated from BB. The approach developed here may be applied elsewhere to screen region-specific OC / levoglucosan ratios for estimating appropriate atmospheric concentrations of OC_BB, aiding the establishment of BB control measures.

We show that aerosol acidity (pH) and liquid water content naturally emerge as previously ignored parameters that drive particulate matter formation in the atmosphere, and its sensitivity to emissions of ammonia and nitric acid. The simple framework presented is easily applied to ambient measurements or model output, and it provides the chemical regime of PM sensitivity to ammonia and nitric acid availability.

Methanesulfonic acid (MSA) is important to the CCN in the MBL. The uptake of MSA on particles is lacking in knowledge. The characteristics of MSA uptake on different particles were studied in the Southern Ocean. The MSA uptake on different particles was associated with particle properties. Uptake of MSA on sea salt particles was favored, while acidic and hydrophobic particles suppressed the MSA uptake. The results extend the knowledge of MSA formation and behavior in the atmosphere.