To investigate the summer ozone pollution, observationally constrained modelling was carried out to study atmospheric oxidation capacity (AOC), OH reactivity, OH chain length, and HO_x budget for three different ozone concentration levels in Shanghai, China. It shows that AOC, dominated by reactions involving OH radical during the daytime, has a positive correlation with ozone levels. Some key VOCs species are very important for the OH reactivity and also the ozone formation potential.

Our multi-year observational study regarding organic aerosol (OA) in the Po Valley indicates that more than half of OA is of secondary origin (SOA) through all the year and at both urban and rural sites. Within the SOA, the measurements show the importance of biomass burning (BB) aging products during cold seasons and indicate aqueous-phase processing of BB emissions as a fundamental driver of SOA formation in wintertime, with important consequences for air quality policy at the global level.

The research apportions size-resolved aerosol contributions from the South China Sea during the Vasco research cruise in September 2011. As aerosols can affect precipitation rates and cloud formation, identifying sources is key to characterizing the region and developing our understanding of aerosol–cloud behavior. A strong biomass burning signal was identified using elemental particulate matter in the fine and ultrafine size ranges. Oil combustion, soil dust, and sea spray were also identified.

Arctic clouds constitute a large source of uncertainty in predictions of future climate. Observations indicate that the number concentration of cloud ice crystals exceeds the concentration of aerosols that can act as ice-nucleating particles (INPs). We show that ice multiplication due to mechanical break-up upon collisions between the few primary ice crystals (formed from INPs) can explain the discrepancy. Including a description of the process in climate models can improve cloud representation.

Marine stratocumulus clouds cover large regions of the ocean and act to cool the climate. We use high-resolution simulations to understand how observed layers of elevated smoke impact stratocumulus via the solar heating that occurs within the smoke layer. We find that the cloud response is strongest for thin, dense layers of smoke close to the cloud. The response rapidly weakens as the cloud-to-smoke gap increases. Generally, the smoke acts to thicken clouds and enhance their cooling effect.

Differences in methane lifetime among global models are large and poorly understood. We use a neural network method and simulations from the Chemistry Climate Model Initiative to quantify the factors influencing methane lifetime spread among models and variations over time. UV photolysis, tropospheric ozone, and nitrogen oxides drive large model differences, while the same factors plus specific humidity contribute to a decreasing trend in methane lifetime between 1980 and 2015.

The amount of the micronutrient selenium in food largely depends on the amount and form of selenium in soil. The atmosphere acts as a source of selenium to soils through deposition, yet little information is available about atmospheric selenium cycling. Therefore, we built the first global atmospheric selenium model. Through sensitivity and uncertainty analysis we determine that selenium can be transported thousands of kilometers and that measurements of selenium emissions should be prioritized.

This study attempts identification of mechanisms of secondary ice production (SIP) based on the observation of small faceted ice crystals. It was found that in both mesoscale convective systems and frontal clouds, SIP was observed right above the melting layer and extended to the higher altitudes with colder temperatures. A principal conclusion of this work is that the freezing drop shattering mechanism is plausibly accounting for the measured ice concentrations in the observed condition.

We characterized the aerosol particles in Cabo Verde at sea and cloud levels. We found four well-separable types of PNSDs, with the strongest differences between air masses coming from the ocean compared to from the African continent. During the strongest observed dust periods, CCN concentrations were 2.5 higher than during clean marine periods. The hygroscopicity of the particles did not vary much between different periods. Aerosol at sea level and on the mountaintop was well in agreement.

In this study, we examined number concentrations of ice nucleating particles (INPs) at Cabo Verde in the oceanic sea surface microlayer and underlying seawater, in the air close to both sea level and cloud level, and in cloud water. The results show that most INPs are supermicron in size, that INP number concentrations in air fit well to those in cloud water and that sea spray aerosols at maximum contributed a small fraction of all INPs in the air at Cabo Verde.

Seasonal atmospheric processing of NOCs was investigated using single-particle mass spectrometry in urban Guangzhou. The abundance of NOCs was found to be strongly enhanced by internal mixing with photochemically produced secondary oxidized organics. A multiple linear regression analysis and a positive matrix factorization analysis were performed to predict the relative abundance of NOCs. More than 70 % of observed NOCs could be well explained by oxidized organics and ammonium.

We analyze 15 years of satellite observations of nitrogen dioxide (NO₂) and use an atmospheric chemistry model to understand the seasonal changes and trends in nitrogen oxides (NO_x) over China. We show that the seasonal changes in NO₂ occur due to changes in the NO_x oxidation lifetime. We find that Chinese NO_x emissions peaked in 2011 and had decreased by about 25 % by 2018. But the decrease in NO₂ in winter was larger, likely because of a simultaneous decrease in the NO_x oxidation lifetime.

We quantified the relative influences of anthropogenic emissions and meteorological conditions on PM_2.5 concentrations in Beijing over the winters of 2002–2016. Meteorological conditions over the study period would have led to an increase of haze in Beijing, but the strict emission control measures have suppressed the unfavorable influences of the recent climate.

This study investigates intercontinental transport of dust plums and distribution characteristics of dust at different altitudes over the Tibetan Plateau (TP). The results show that dust particles are emitted into atmosphere and then transport to the TP. The East Asian dust trasnports southward and is lifted up to the TP in northern slop, while the North Afican dust and Middle East dust transport eastward and concentrate in both northern and southern slops, then is lifted up to the TP.

We characterized various optical, chemical, and physical properties of particles produced from combustion of a variety of different biomass fuels, many representative of those found in the western US. We find that many properties scale with the ratio between bulk average organic aerosol and black carbon mass concentrations, although there are some properties that do not.

Particulate matter (PM) emitted from ships has gained more attention in recent decades. Organic matter, elemental carbon, water-soluble ions and heavy metals in PM and particle numbers are the main points. However, studies of detailed chemical compositions in particles with different size ranges emitted from ships are in shortage. This study could bring new and detailed measurement data into the field of size-segregated particles from ships and be of great source emission interest.

The southeast Atlantic during August–October experiences layers of smoke from biomass burning over marine stratocumulus clouds. Here we present the light attenuation of the smoke and its dependence in the spatial, vertical, and spectral domain through direct measurements from an airborne platform during September 2016. From our observations of this climatically important smoke, we found an average aerosol optical depth of 0.32 at 500 nm, slightly lower than comparative satellite measurements.

A realistic representation of cloud–aerosol interactions is central to accurate climate projections. Here we combine observations collected during the ACRIDICON-CHUVA campaign with chemistry-transport simulations to evaluate the model’s ability to represent the indirect effects of biomass burning aerosol on cloud microphysics. We find an upper limit for the model sensitivity on cloud condensation nuclei concentrations well below the levels reached during the burning season in the Amazon Basin.

The understanding of cloud processes is based on the quality of the representation of cloud properties. We compared cloud parameters from three models with satellite observations. We report on the performance of each data source, highlighting strengths and deficiencies, which should be considered when deriving the effect of aerosols on cloud properties.

Since numerical air quality models do not explicitly simulate stochastic variations in the atmosphere, there will always be differences between modeled and measured pollutant levels even when the model's physics, chemistry, numerical analysis, and its input data are perfect. This paper quantifies the inherent uncertainty in regional models due to the stochastic nature of the atmosphere. A knowledge of the expected error helps model developers in evaluating the real progress in improving models.

Black carbon is believed to be one of the causes of the rapid warming and glacier melting in the Arctic. The results of our study show that processes associated with the petroleum industry, such as gas flaring in Russia, are the main BC source at the Arctic surface. Emissions in East Asia are the main BC sources at high altitudes in the Arctic. Wildfires in Siberia, Alaska, and Canada are another important Arctic BC source in summer.

A source apportionment study of hourly resolved elements in PM₁₀ measured at a traffic-influenced site in Härkingen, Switzerland, using positive matrix factorization (PMF) and multilinear engine-2 (ME-2) offered resolution of robust and unambiguous factor profiles and contributions. We show that the rotational control available in ME-2 provides a means for treating extreme events such as fireworks within a PMF analysis.

Air–sea exchanges during Mediterranean heavy precipitation events are key and their representation must be improved for high-resolution weather forecasts. This study investigates the mechanisms acting at the air–sea interface during a case that occurred in southern France. To focus on the impact of sea state, we developed and used an original coupled air–wave model. Results show modifications of the forecast for the air–sea fluxes, the near-surface wind and the location of precipitation.

The study reports the transition in the atmospheric emission of particles and gases from on-road heavy-duty trucks (HDTs) caused by the modernisation of the fleet. We measured particle number (PN), particle mass (PM), black carbon (BC), nitrogen oxides (NO_x), carbon monoxide (CO), hydrocarbon (HC), particle size distributions, and volatility in the plumes of 556 individual HDTs. Significant but different changes in emissions were evident for various pollutants with respect to emission standards.

In this study, land surface and atmosphere interactions are addressed using ground-based remote sensing, satellite products, and high-resolution large-eddy simulations. The focus is on water vapor transport from the surface into the atmosphere. Patterns found in long-term observations can be linked to properties of the surrounding land surface. The simulation results suggest that a different distribution of land use types has implications for boundary layer characteristics and clouds.

We study the presence and characteristics of 27 d solar signatures in middle atmospheric temperature observed by the microwave limb sounder on NASA's Aura spacecraft. This is a highly interesting and significant subject because the physical and chemical mechanisms leading to these 27 d solar-driven signatures are, in many cases, not well understood. The analysis shows that highly significant 27 d solar signatures in middle atmospheric temperature are present at many altitudes and latitudes.

Long-term exposure to ambient ozone is associated with a variety of impacts, including adverse human-health effects and reduced commercial crop yields. We apply machine learning to empirically model long-term O₃ exposure over the continental United States from 2000 to 2015 and generate a measurement-based assessment of impacts on human health and crop yields. Notably, our results illustrate how different conclusions regarding historical impacts can be drawn through the use of varying metrics.

Bacteria in the atmosphere are important due to their potential adverse health effects and as initiators of ice cloud formation. Observational studies suggest that bacterial cells grow and multiply in clouds and also consume organic compounds. We estimate the role of microbial processes in the atmosphere for (i) the increase in biological aerosol mass by cell growth and multiplication and (ii) the sink strength of organics in clouds as a loss process in addition to chemical reactions.

Emission data contain uncertainties introduced by the methodology and the data used. We quantified uncertainties in gridded emissions using the uncertainty in underlying data, showing that disaggregation in space and time significantly increases the uncertainty. Understanding uncertainties helps to interpret atmospheric measurements and the gap with modelled concentrations. Moreover, our analyses help identify regions with large uncertainties, which require further scrutiny.

Airborne biological particles impact human health, cloud formation, and ecosystems, but few techniques are available to characterize their atmospheric abundance. Combining a newly developed high-volume sampling/flow cytometry technique together with an laser-induced fluorescence instrument, we detect a highly dynamic bioaerosol community over urban Atlanta, composed of pollen, fungi, and bacteria with low and high nucleic acid content.

An episode of anomalously low ozone concentrations in the stratosphere over northern Europe occurred on 3–5 November 2018. The 30 % reduction of the ozone layer was predicted by the global chemistry-transport model of the Finnish Meteorological Institute driven by weather forecasts of ECMWF. The reduction was subsequently observed by ozone monitoring satellites. The episode was caused by a storm in the northern Atlantic, which uplifted air from the troposphere to stratosphere.

The solubility of atmospheric iron is important in human health and environmental chemistry. To understand the origin of water-soluble iron in urban areas, tailpipe emissions were collected from 32 low-emitting vehicles, from which iron solubility averaged 30 % (0–82 %), more than 10 times the average in the Earth's crust. Water-soluble iron was independent of almost all exhaust components and of the iron phase in the particles but was correlated with specific exhaust-derived organic compounds.