Several ozone composites show different decadal trends, even in composites built with the same data. We remove artefacts affecting trend analysis with a new method (BASIC) and construct an ozone composite, with uncertainties. We find a significant ozone recovery since 1998 in the midlatitude upper stratosphere, with no hemispheric difference. We recommend using a similar approach to construct a composite based on the original instrument data to improve stratospheric ozone trend estimates.

Boreal Siberia is a unique region with severe wildfire activity which is little studied today. We employ unique ground-based observations of major biomass burning products obtained during TRanscontinental Observations Into the Chemistry of the Atmosphere (TROICA) expedition along the Trans-Siberian Railway to provide information about chemical composition of forest fire plumes in Siberia. The results may be used in studies related to climate change and regional air quality.

The governing factors for new particle formation (NPF) events in Beijing were analyzed. The roles of gaseous precursors and aerosol surface area were illustrated. It appears that the abundance of gaseous precursors in Beijing is high enough to have nucleation; however, it is aerosol surface area that determines the occurrence of NPF events in Beijing. Aerosol loading thresholds (in the form of aerosol surface area and PM_2.5 concentration) for predicting NPF days in Beijing were suggested.

This work presents the features and evaluates the quality of the Copernicus Atmospheric Monitoring Service forecasts of olive pollen distribution in Europe. It is shown that the models can predict the main features of the observed pollen distribution but have more difficulties in capturing the season start and end, which appeared shifted by a few days. We also demonstrated that the combined use of model predictions with up-to-date measurements (data fusion) can strongly improve the results.

This work addresses unclear roles of heterogeneous N₂O₅ reactions and chlorine activation processes in the polluted residual layer from a mountaintop measurement in northern China. The results revealed efficient ClNO₂ production in the coal-fired plumes in this region, having large impacts on next-morning photochemistry. Fast heterogeneous N₂O₅ reactions dominate the nocturnal NO_x loss and contribute to substantial nitrate formation, which may boost the haze pollution in northern China.

Measurements of airborne particulate matter have been conducted using a scanning mobility particle sizer at a site in the vicinity of Heathrow Airport, London. The measured particle size distributions have been assessed both by k means clustering and PMF analysis in conjunction with measurements of meteorological variables and chemical composition. The results give a quantitative estimate of the impact of aircraft and airport emissions on local air quality.

Methane is a potent greenhouse gas, and leaks from natural gas infrastructure are thought to be a significant emission source. We used a mobile survey method to measure GHGs near Canadian infrastructure. Our results show that ~ 47 % of active wells were emitting. Abandoned and aging wells were also associated with emissions. We estimate methane emissions from this development are just over 111 Mt year⁻¹, which is more than previous government estimates, but less than similar studies in the US.

First study to our knowledge to quantify the influence extratropical cyclones have on the temporal variability of springtime surface ozone (O₃) measured on the west coast of Europe when cyclones are nearby. We show passing cyclones have a discernible influence on surface O₃ concentrations. In-depth findings from four case studies, using a combination of reanalyses and a modeled tracer, demonstrate there are several transport pathways before O₃-rich air eventually reaches the surface.

We extend CMAQ's applicability to the entire Northern Hemisphere to enable consistent examination of interactions between atmospheric processes occurring on various spatial and temporal scales. Improvements were made in model process representation, structure, and input data sets that enable a range of model applications including episodic intercontinental pollutant transport, long-term trends in air pollution across the Northern Hemisphere, and air pollution–climate interactions.

Stratospheric particles were collected in the polar stratosphere in winter 1999/2000. Besides the well-studied volatile particles from that region, the main findings of this study are stable carbonaceous particles in the sub-micrometer size range. In addition to carbon, many particles show the elements Si, Fe, Cr and Ni to a minor amount. Based on exclusion, carbonaceous material from IDPs and residues from meteoric ablation and fragmentation remain as the most probable sources.

This study highlights the importance of independent global measurements with high and long-term accuracy to quantify long-term changes, especially in the UTLS region, and to help identify inconsistencies between different data sets of observations and models. Here we investigated temperature trends over different regions within a climate-sensitive area of the atmosphere and demonstrated the value of the IAGOS temperature observations as an anchor point for the evaluation of reanalyses.

We present a merged dataset of ozone profiles from several satellite instruments: SAGE II, GOMOS, SCIAMACHY, MIPAS, OSIRIS, ACE-FTS and OMPS. For merging, we used the latest versions of the original ozone datasets. The merged SAGE–CCI–OMPS dataset is used for evaluating ozone trends in the stratosphere through multiple linear regression. Negative ozone trends in the upper stratosphere are observed before 1997 and positive trends are found after 1997.

Using global and regional models, we determined the anthropogenic increment to ozone (base-case simulation minus a background simulation with only natural emissions) for the US and allocated the increment to anthropogenic emissions inside and outside the US. For the larger ozone concentrations in the base case, the relative importance of the sources is generally US emissions > anthropogenic lateral boundary concentrations (BCs) > Canadian/Mexican emissions ≫ anthropogenic top BCs.

The paper provides an overview of CH₄, CO₂, and CO mixing ratios, including diurnal and seasonal variation, and discusses the association of potential sources and meteorology with the observed temporal variation in the Kathmandu Valley. The study will provide an important dataset for a poorly studied region and will be useful for validating estimates from emission inventories, regional models, and satellite observations and assisting in the design of mitigation measures in the region.

We investigated the optical and chemical properties and direct radiative effects of aerosols in the Kathmandu Valley. We concluded that the ratio of light-absorbing to scattering aerosols as well as the concentration of light-absorbing aerosols is much higher at Kathmandu than other comparable regions, and it contributes to a great atmospheric absorption efficiency. This study provides unprecedented insights into aerosol optical properties and their radiative forcings in the Kathmandu Valley.

This study shows difficulties in interpreting columnar dry-air mole fractions of methane (XCH₄) for surface emissions of CH₄ over the South Asia region, without separating the role of chemistry and transport. Using a chemistry-transport model, we suggest that a link between surface emissions and higher levels of XCH₄ is not always valid in this region of complex monsoonal meteorology, although there is often a fair correlation between the seasonal variations in surface emissions and XCH₄.

Our paper presents results of hydroxyl radical (OH) reactivity from a field study conducted during summer 2013 in a western Mediterranean coastal site (Corsica, France). Here, the total OH reactivity, measured with the comparative reactivity method, is compared with the summed OH reactivity from the reactive gases measured with a multitude of different technologies. Our results demonstrate the relatively high observed reactivity and the large impact of biogenic compounds.

Widely used formulae underestimate the atmospheric new particle formation (NPF) rate when intense NPF events are analyzed. This is caused by the underestimation or neglect of the coagulation scavenging effect. To address this issue, a new formula was theoretically derived. Aerosol down to ~ 1 nm was measured in Beijing and used together with data reported in the literature to test the new formula and others. Implications for NPF rates in various atmospheric environments are discussed.

In the fall of 2011, iodine-131 (¹³¹I) was detected at several radionuclide monitoring stations in central Europe. We estimate the source location and emission variation using only the available ¹³¹I measurements. Subsequently, we use the IAEA report about the source term for validation of our results. We find that our algorithm could successfully locate the actual release site. The findings are also in agreement with the values reported by the IAEA.

This study proposes models to estimate the UVER diffuse irradiance, which means, at least, 40 % of the ultraviolet solar radiation reaching the Earth's surface at mid-latitudes. These models are inspired by expressions originally used to estimate total diffuse fraction and rely on variables commonly available to favor their applicability. The best model in this paper performs better than previous approaches and no additional information about the cloud or aerosol layer is needed.

The VOC emission inventory has large uncertainties. An updated VOC emission inventory of vehicles in China was developed based on a set of state-of-the-art methods and big data. Exhausts and evaporation were taken into account. Our results narrowed the gap between inventories and the real emissions. Detailed speciation reveals the chemical characteristics of emissions, which has the potential to improve the understanding of atmospheric chemical processes in polluted regions.

Shallow maritime clouds make a well-known transition from stratocumulus to trade cumulus with flow from the subtropics equatorward. Three-day large-eddy simulations that investigate the potential influence of overlying African biomass burning plumes during that transition indicate that cloud-related impacts are likely substantially cooling to negligible at the top of the atmosphere, with magnitude sensitive to background and perturbation aerosol and cloud properties.

Ozone and water vapor in the stratosphere are important gases that affect surface climate and absorb incoming solar ultraviolet radiation. These gases are represented in reanalyses, which create a complete picture of the state of Earth's atmosphere using limited observations. We evaluate reanalysis water vapor and ozone fidelity by intercomparing them, and comparing them to independent observations. Generally reanalyses do a good job at representing ozone, but have problems with water vapor.

Black carbon (BC) deposition enhances Arctic warming and melting. We present Svalbard ice core BC data from 2005 to 2015, comparing the results with chemical transport model data. The ice core and modelled BC deposition trends clearly deviate from measured and observed atmospheric concentration trends, and thus meteorological processes such as precipitation and scavenging efficiency seem to have a stronger influence on the BC deposition trend than BC emission or atmospheric concentration trends.

Our results reveal the formation of NH₄HC₂O₄ and NH₄HSO₄ from the reaction of oxalic acid (OA) with ammonium sulfate within aerosols during the slow dehydration compared to the rapid dehydration process. The hygroscopic growth of mixed particles at high RH upon hydration is substantially lower than that of the corresponding dehydration process due to the significant formation of low hygroscopic NH₄HC₂O₄ and residual OA. These findings have important implications for atmospheric chemistry.

This study shows that agricultural emissions are important for air quality and their reduction can effectively reduce the concentration of fine particles and their associated premature mortality. Therefore, emission control policies, especially in North America and Europe, should also involve strong ammonia emission decreases to optimally reduce fine-particle concentration.

Besides the well-known large impact on agriculture and water resources, drought is associated with significant adverse effects on air quality. Drought-induced degradation of air quality is largely due to natural processes, offsetting the effort of anthropogenic emission reduction during the past decades. Such adverse impacts should be included in modeling processes under current and future climate for mitigation policy.

This paper is a study about the mixed-phase clouds frequently occurring in the Arctic region. It is based on airborne measurements and highlights the microphysical properties of these particular clouds composed of liquid droplets at cloud top and ice crystals below precipitating down to the surface. This work may help to improve the representation of the mixed-phase clouds in numerical prediction models as well as the retrieval of their properties from remote sensing observations.