The present work aims at identifying and quantifying the relative contributions of the key factors in driving a rapid increase in summertime surface O₃ over the North China Plain during 2013–2019. In addition to anthropogenic emission reduction and meteorological variabilities, our study highlights the importance of inclusion of aerosol absorption and scattering properties rather than aerosol abundance only in accurate assessment of aerosol radiative effect on surface O₃ formation and change.

The south-eastern Atlantic is semi-permanently covered by some of the largest stratocumulus clouds and is influenced by one-third of the biomass burning emissions from African fires. A UKEMS1 model simulation shows that the absorption effect of biomass burning aerosols is the most significant on clouds and radiation. The dominate cooling and rapid adjustments induced by the radiative effects of biomass burning aerosols result in an overall cooling in the south-eastern Atlantic.

Seasonal rainfall amounts along the densely populated West African Guinea coast have been decreasing during the past 35 years, with recently accelerating trends. We find strong indications that this is in part related to increasing human air pollution in the region. Given the fast increase in emissions, the political implications of this work are significant. Reducing air pollution locally and regionally would mitigate an imminent health crisis and socio-economic damage from reduced rainfall.

Climate models predict a shift toward warmer, drier environments in southwestern North America. Under future climate, the two main drivers of dust trends play opposing roles: (1) CO₂ fertilization enhances vegetation and, in turn, decreases dust, and (2) increasing land use enhances dust emissions from northern Mexico. In the worst-case scenario, elevated dust concentrations spread widely over the domain by 2100 in spring, suggesting a large climate penalty on air quality and human health.

Observations in previous studies show that cloud droplets carry electric charges. We are curious about whether the electric interaction enhances the collision of cloud droplets. The effect of the electric charge and atmospheric electric field on the raindrop-formation process is studied numerically. Results indicate that a cloud with a small droplet size is more sensitive to an electric charge and field, which could significantly trigger droplet collision and accelerate raindrop formation.

Simulated aerosol optical properties as well as the aerosol life cycle are investigated for 14 global models participating in the AeroCom initiative. Considerable diversity is found in the simulated aerosol species emissions and lifetimes, also resulting in a large diversity in the simulated aerosol mass, composition, and optical properties. A comparison with observations suggests that, on average, current models underestimate the direct effect of aerosol on the atmosphere radiation budget.

Organic nitrates formed from the oxidation of biogenic volatile organic compounds impact both ozone and particulate matter as they remove nitrogen oxides, but they represent important aerosol precursors. We conducted a series of reaction chamber experiments that quantified the total organic nitrate and secondary organic aerosol yield from the OH-radical-initiated oxidation of ocimene, and also measured their hydrolysis lifetimes in the aqueous phase, as a function of pH.

Black carbon (BC) is a component of particulate matter which has significant effects on climate and human health. Sources of BC include biomass burning, transport, industry and domestic cooking and heating. In this study, we measured BC emissions in Beijing, finding a dominance of traffic emissions over all other sources. The quantitative method presented here has benefits for revising widely used emissions inventories and for understanding BC sources with impacts on air quality and climate.

To investigate the sources of free amino acids (FAAs) in the marine atmosphere, concerted measurements (the simultaneous investigation of seawater, size-segregated aerosol particles and cloud water) were performed at the Cabo Verde islands. This study describes the transfer of FAAs as part of organic matter from the ocean into the atmosphere on a molecular level. In the investigated marine environment, a high enrichment of FAAs in submicron aerosol particles and in cloud droplets was observed.

In this study, we investigate three patterns of new particles growing to CCN (cloud condensation nuclei) size, i.e., one-stage growth and two-stage growth-A and growth-B patterns. Combining the observations of gaseous pollutants and measured or modeled particulate chemical species, the three growth patterns were discussed regarding the spatial heterogeneity, formation of secondary aerosols, and evaporation of semivolatile particulates as was the survival probability of new particles to CCN size.

The solar signal in the mesospheric H₂O and CO was extracted from the CCMI-1 model simulations and satellite observations using multiple linear regression (MLR) analysis. MLR analysis shows a pronounced and statistically robust solar signal in both H₂O and CO. The model results show a general agreement with observations reproducing a negative/positive solar signal in H₂O/CO. The pattern of the solar signal varies among the considered models, reflecting some differences in the model setup.

We propose a new atmospheric coordinate (M_θe) based on equivalent potential temperature (θ_e) but with mass as the unit. This coordinate is useful in studying the spatial and temporal distribution of long-lived chemical tracers (CO₂, CH₄, O₂ / N₂, etc.) from sparse data, like airborne observation. Using this coordinate and sparse airborne observation (HIPPO and ATom), we resolve the Northern Hemisphere mass-weighted average CO₂ seasonal cycle with high accuracy.

Field measurements were conducted to confirm the arrival of African dust on the Yucatàn Peninsula. Aerosol particles were monitored at ground level by different online and off-line sensors. Several particulate matter peaks were observed with a relative increase in their levels of up to 500 % with respect to background conditions. Based on the chemical composition, back trajectories, vertical profiles, reanalysis, and satellite images, it was found that the peaks are linked to African dust.

Forest fires are an important source of reactive organic gases and aerosols to the atmosphere. We analyzed organic aerosols collected from an aircraft above a boreal forest fire and reported an increasing contribution from compounds containing oxygen, nitrogen, and sulfur as the plume aged, with sulfide and ring-bound nitrogen functionality. Our results demonstrated chemistry that is important in biomass burning but also in urban/developing regions with high local nitrogen and sulfur emissions.

We make the first quantitative, remote-sensing-based, and hemisphere-scale assessment of radiative forcing (RF) due to light-absorbing particles (LAPs) in snow. We observed significant spatial variations in snow albedo reduction and RF due to LAPs throughout the Northern Hemisphere, with the lowest values occurring in the Arctic and the highest in northeastern China. We determined that the LAPs in snow play a critical role in spatial variability in Northern Hemisphere albedo reduction and RF.

This paper provides interesting new results on the thermodynamic structure of the boundary layer, cloud conditions, and fog characteristics in the Arctic during the Arctic Ocean 2018 campaign. It provides information for interpreting further process studies on aerosol–cloud interactions and shows substantial differences in thermodynamic conditions and cloud characteristics based on comparison with previous campaigns. This certainly raises the question of whether it is just an exceptional year.

Photochemistry of iron(III) complexes plays an important role in aerosol aging, especially in the lower troposphere. Ensuing radical chemistry leads to decarboxylation, and the production of peroxides, and oxygenated volatile compounds, resulting in particle mass loss due to release of the volatile products to the gas phase. We investigated kinetic transport limitations due to high particle viscosity under low relative humidity conditions. For quantification a numerical model was developed.

It was observed that friagem phenomena (incursion of cold waves from the high latitudes of the Southern Hemisphere to the Amazon region), very common in the dry season of the Amazon region, produced significant changes in microclimate and atmospheric chemistry. Moreover, the effects of the friagem change the surface O₃ and CO₂ mixing ratios and therefore interfere deeply in the microclimatic conditions and the chemical composition of the atmosphere above the rainforest.

A lack of consistent observational constraints on the atmospheric evolution of the optical properties of biomass burning (BB) aerosol limits the accuracy of assessments of the aerosol radiative and climate effects. We show that useful insights into the evolution of the BB aerosol optical properties can be inferred from a combination of satellite observations and 3D modeling. We report major changes that occurred in the optical properties of Siberian BB aerosol during its long-range transport.

We analyzed 26-year CH₄ measurements at Mount Waliguan in the Tibetan Plateau, China. The CH₄ increased ~ 133 parts per billion (ppb) with a rate of 5.1 ± 0.1 ppb yr^-1 from 1994 to 2019. Major source regions were identified in northeast and southwest. The influence of human activities is more and more serious, and northern India has possibly become a stronger contributor than city regions were in the past. It has become urgent to control CH₄ emissions in the Tibetan Plateau.

The effect of aerosols on regional climate simulations presents large uncertainties due to their complex and non-linear interactions with a wide variety of factors, including aerosol–radiation and aerosol–cloud interactions. We show how these interactions are strongly conditioned by the meteorological situation and the type of aerosol. While natural aerosols tend to increase precipitation in some areas, anthropogenic aerosols decrease the number of rainy days in some pollutant regions.

Here we describe the vertical profiles of extensive (scattering and absorption) and intensive (e.g. albedo and asymmetry parameter) aerosol optical properties from coupling ground-based measurements from two sites in north-eastern Spain and airborne measurements performed with an aircraft. We analyse different aerosol layers along the vertical profile for a regional pollution episode and a Saharan dust intrusion. The results show a change with height depending on the different measured layers.

We simulate the atmospheric chemical processes of an important sulfur-containing organic aerosol species, which is produced by the reaction between sulfur dioxide and formaldehyde. We can predict its distribution on a global scale. We find it is particularly rich in East Asia. This aerosol species is more abundant in the colder season partly because of weaker sunlight.

Intense and localised emissions of pollutants are common in urban environments, in which turbulence cannot mix these segregated pollutants efficiently in the atmosphere. Despite their relatively high resolution, regional models cannot resolve such segregation and assume instantaneous mixing of these pollutants in their model grids, which potentially induces significant error in the subsequent chemical calculation, based on our calculation with a model that explicitly resolves turbulent motions.

We combine spaceborne lidar observations of clouds in the troposphere and stratosphere to assess the outcome of ground-based polar stratospheric cloud (PSC) observations that are often performed at the mercy of tropospheric clouds. We find that the outcome of ground-based lidar measurements of PSCs depends on the location of the measurement. We also provide recommendations regarding the most suitable sites in the Arctic and Antarctic.

This paper summarizes Finnish Meteorological Institute and Kansas State University unmanned aerial vehicle measurements during the summer 2018 Lower Atmospheric Process Studies at Elevation – a Remotely-piloted Aircraft Team Experiment (LAPSE-RATE) campaign in the San Luis Valley, providing an overview of the rotorcraft deployed, payloads, scientific goals and flight strategies and presenting observations of atmospheric thermodynamics and aerosol and gas parameters in the vertical column.

The year 2019 was particularly rich for the stratospheric aerosol layer due to two volcanic eruptions (at Raikoke and Ulawun) and wildfire events. With satellite observations and models, we describe the exceptionally complex situation following the Raikoke eruption. The respective plume overwhelmed the Northern Hemisphere stratosphere in terms of aerosol load and resulted in the highest climate impact throughout the past decade.

We address the phenomenon of ice enhancement in the vicinity of warm hydrometeors using highly accurate flow simulation techniques. It is found that the transiently supersaturated zones induced by the hydrometeor's wake are by far larger than what has been previously estimated. The ice enhancement is quantified on the micro- and macroscale, and its relevance is discussed. The results provided may contribute to a (currently unavailable) parametrization of the phenomenon.

We investigate the vertical distribution of aerosol in the climate model NorESM1-M in five regions of marine stratocumulus clouds. We thereby analyze the total aerosol extinction to facilitate a comparison with satellite data. We find that the model underestimates aerosol extinction throughout the troposphere, especially elevated aerosol layers. Further, we perform sensitivity experiments to identify the processes most important for vertical aerosol distribution in our model.