Measurements at high-Arctic sites show a strong annual cycle in atmospheric particle number and size. Previous studies identified poor scientific understanding related to global model representation of Arctic particle number and size, limiting ability to simulate this environment. Here we evaluate state-of-science ability to simulate Arctic particles using GEOS-Chem-TOMAS model, documenting key roles and interconnections of particle formation, cloud-related processes and remaining uncertainties.

Greenhouse gas emissions can be assessed by "top-down" methods that combine atmospheric observations, a transport model and a mathematical optimisation framework. Here, we apply such a top-down method to the methane emissions of Switzerland, utilising observations from the recently installed CarboCount-CH network. Our Swiss total emissions largely agree with those of the national "bottom-up" inventory, whereas regional differences suggest lower than reported emissions from manure handling.

We constructed a model of carbonyl sulfide soil exchange sufficient for predicting outcomes in terrestrial ecosystems. Empirical observations combined with soil gas exchange theory reveal simultaneous abiotic production and biotic uptake mechanisms. Measurement of atmospheric carbonyl sulfide is an emerging tool to quantify photosynthesis at important temporal and spatial scales.

We use PMCAMx with high grid resolution over Paris to simulate carbonaceous aerosol during the summer and winter MEGAPOLI campaigns. PMCAMx reproduces BC observations well. Addition of cooking organic aerosol emissions of 80 mg per day per capita is needed to reproduce the corresponding observations. While the oxygenated organic aerosol predictions during the summer are encouraging a major wintertime source appears to be missing.

Here we present a day of case study measurements of the vertical distribution of bromine monoxide over the coastal region of the Gulf of Mexico. These measurements are used to assess the contribution of bromine radicals to the oxidation of elemental mercury in the troposphere. We find that the measured levels of bromine in the troposphere are sufficient to quickly oxidize mercury, which has significant implications for our understanding of atmospheric mercury processes.

We use climate simulations, paleoclimate data and modern observations to infer that continued high fossil fuel emissions will yield cooling of Southern Ocean and North Atlantic surfaces, slowdown and shutdown of SMOC & AMOC, increasingly powerful storms and nonlinear sea level rise reaching several meters in 50–150 years, effects missed in IPCC reports because of omission of ice sheet melt and an insensitivity of most climate models, likely due to excessive ocean mixing.

Atmospheric emissions from small forest fires and their impact on regional air quality are still poorly characterized. We used an instrumented NASA P-3B aircraft to study emissions from a small forest understory fire in Georgia (USA) and to investigate chemical transformations in the fire plume in the 1 h downwind region. A state-of-the-art chemical model was able to accurately simulate key chemical processes in the aging plume.

The interplay of European air quality policies and technological advancement to reduce anthropogenic emissions avoided a dramatic deterioration of air quality in Europe and beyond over the last 40 years (e.g. fuel quality directives reduced global SO₂ emissions by 88 %, while the EURO standards led to a 50 % reduction of PM_2.5). The story told by the EDGAR retrospective scenarios can be informative for designing multi-pollutant abatement policies also in emerging economies.

Combining ¹⁴C and ¹³C data from the Los Angeles, CA megacity with background data allows source attribution of CO₂ emissions among biosphere, natural gas, and gasoline. The 8-year record of CO₂ emissions from fossil fuel burning is consistent with "The Great Recession" of 2008–2010. The long-term trend and source attribution are consistent with government inventories. Seasonal patterns agree with the high-resolution Hestia-LA emission data product, when seasonal wind directions are considered.

Ascorbic acid (AA) and Dithiothreitol (DTT) assay measures of water-soluble PM_2.5 oxidative potential (OP) are compared in terms of spatiotemporal trends, chemical selectivity, sources, and health impacts based on an epidemiological study with backcast estimated OP. Both assays point to metals from brake/tire wear, but only the DTT assay also identifies organics from combustion. DTT is associated with emergency department visits for asthma/wheeze and congestive heart failure, whereas AA is not.

The Weather Research and Forecast model is used to simulate a large-scale tropical tropopause layer (TTL) cirrus. Validated with satellite observations, the simulation shows that several clouds successively form due to a large-scale uplift initiated by the intrusion of air from the midlatitudes. The simulated cloud field is found as sensitive to the initial condition as it is to the choice of the microphysics parametrisation. The cloud impacts on the radiative and water budgets are estimated.

For a long time, it was thought that tropical rainforests are evergreen forests and the processes involved in these ecosystems do not change all year long. However, some satellite retrievals have suggested that ecophysiological processes may present seasonal variations mainly due to variation in light and leaf phenology in Amazonia. These in situ measurements are the first showing of a seasonal trend of volatile organic compound emissions, correlating with light and leaf phenology in Amazonia.

This work tests the use of an ensemble prediction system for aerosol forecasting, including an ensemble adjustment Kalman filter for MODIS AOT assimilation. Key findings include (1) meteorology and source-perturbed ensembles are needed to capture long-range transport and near-source aerosol events, (2) adaptive covariance inflation is recommended for assimilating spatially heterogeneous observations and (3) the ensemble system captures sharp gradients relative to a deterministic/variational system.

This study provides systematic and scientific representation of greenhouse gases (CO₂ and CH₄) and its dynamics at a suburban site of India. It was required to generate reliable, highly precise, and accurate measurements of CO₂ and CH₄ over this part of the world. We made use of high-precision greenhouse gases measurements recorded by LGR-GGA instrument also by complementary data from remote sensing satellites as well as from automatic weather station.

In this paper, we find that the daily maximum 8 h O₃ in the eastern China has undergone a significant increase during 2003–2015, with a rate of 1.1 ppb per year. The increase of surface ozone was mainly induced by the emission changes and the meteorological factors just played a tiny negative influence. Our result also indicates that VOCs seem to play more important role in the ozone increase than the effect of NO titration.

First deployment of PTR-TOF-MS in South Asia. High acetaldehyde and biogenic isoprene concentrations detected even in winter in the Kathmandu Valley. Isocyanic acid, formamide, acetamide, naphthalene and nitromethane were detected for the first time in South Asian air. Oxygenated VOCs and isoprene-dominated OH reactivity and ozone production potentials (> 68 % OPP). Regulation of emissions from biomass co-fired brick kilns' by cleaner technology would improve air quality of the valley.

Lidar, radar, and radiosonde observations obtained during large wildfires shed new light on the initiation and development of pyrocumulus and pyrocumulonimbus clouds. Lidar data show, for example, that the condensation level in these towering convective plumes can be significantly higher than the condensation level in the ambient environment. Above the condensation level the subsequent cloud development is shown to be sensitive to wind shear and dry air entrainment, which limit vertical growth.

OH radicals are important intermediates in the atmosphere, and the high concentrations observed in tropical regions are yet to be fully explained. Radical-radical reactions such as the title reaction can contribute to OH formation. This is the most fully comprehensive study of the CH₃C(O)O₂ + HO₂ reaction with direct observation of products in all reaction channels. The implications of the new measurements on OH, PAN and NO_x concentrations are considered via global models.

A simple statistical model to predict the number of aerosols which activate to form cloud droplets in warm clouds has been established, based on regression analysis of data from the high-altitude site Jungfraujoch. It is found that cloud droplet formation at the Jungfraujoch is predominantly controlled by the number concentration of aerosol particles. A statistical model based on only the number of particles larger than 80nm can explain 79 % of the observed variance in droplet numbers.

In this work, organic aerosol (OA) predictions from the volatility basis set (VBS) module in the CMAQ photochemical transport model were evaluated against routine monitoring data and measurements collected during the 2010 CalNex field study. We found that the VBS module more accurately reproduced the observed primary/secondary OA split and secondary OA (SOA) mass at the CalNex Pasadena ground site compared to the traditional CMAQ OA module but still underpredicted observed SOA by ~ 5.2 ×.

Water-soluble organic compounds (WSOCs) play an important role in the hygroscopicity of aerosols. The coexisting hygroscopic species such as levoglucosan, malonic acid, and phthalic acid have a strong influence on hygroscopic growth and phase behavior of oxalic acid, even suppressing its crystallization completely. The hygroscopic species such as levoglucosan in the mixed particles may significantly influence the hygroscopic behavior of ammonium sulfate by changing phase state of oxalic acid.

This study was initiated to identify the sources affecting speciated mercury concentrations measured on the island located between mainland Korea and China. The results from various approaches consistently show that Korean sources are most important for gaseous oxidized form while for other Hg species regional transport was also important. It is also suggested that the secondary formation of particulate Hg becomes more important as the significance of long-range transport increased.

We show the first mercury profile measurements over Europe since 1996. Besides gaseous elemental mercury (GEM) and total gaseous mercury (TGM), the gases CO, SO₂, NO_x, and O₃ were measured from aboard a research aircraft over four European locations. Compared to the boundary layer, the concentration of GEM and TGM in the free troposphere was 10–30% lower. Inside the individual layers no vertical gradient was apparent. Combined with CARIBIC data, a unique profile from 0.4 to 10.5 km is provided.

We propose insights based on atmospheric observations around the Arctic circle to evaluate estimates of methane emissions to the atmosphere from the East Siberian Arctic Shelf. Based on a comprehensive statistical analysis of the observations and of high-resolution transport simulations, annual methane emissions from ESAS are estimated to range from 0.0 to 4.5 TgCH₄ yr⁻¹, with a maximum in summer and very low emissions in winter.

Upper tropospheric humidity (UTH) is a weighted mean of the relative humidity (RH) in the upper troposphere. It can change due to climate change even when the relative humidity would stay unchanged because the weighting functions will alter. We show that changes of UTH expected during 30 years of tropospheric warming are typically less than 1 % in magnitude and mostly negative. Larger positive changes of UTH (as found in an analysis of 30 years of satellite data) point thus to an increase of RH.

The long-term evolution of HCHO in the remote troposphere is characterized using a 27-year time series of total columns from high-resolution FTIR solar spectra recorded at Jungfraujoch. A parametric model is used to remove the effect of the HCHO diurnal variations for improving the trend determination and the comparison with columns simulated by GEOS-Chem. Sensitivity tests are performed to identify the main drivers of the HCHO seasonal and inter-annual variations, as well as their contribution.

Various forms of solar radiation management (SRM) have been proposed to counteract man-made climate change. However, all these countermeasures could have unintended side-effects. We add a novel perspective to this discussion by showing how atmospheric ozone changes under solar geoengineering could affect UV exposure and air pollution. This would have implications for human health and ecology. Atmospheric composition changes are therefore important to consider in the evaluation of any SRM scheme.

The variability of the autumn Arctic sea ice extent, local precipitation and surface wind during winter is most influential to the haze pollution change in eastern China. The joint effect of fast increase of total energy consumption, rapid decline of Arctic sea ice extent and reduced precipitation and surface winds intensified the haze pollution in central North China after 2000. There is similar conclusion for haze pollution in eastern South China after 2000.