Secondary organic aerosol (SOA) is produced through a complex interaction of sunlight, volatile organic compounds emitted from trees, anthropogenic emissions, and atmospheric chemistry. We are able to successfully model the formation and diurnal evolution of SOA using a model that takes into consideration the surface and boundary layer dynamics (1–2 km from the surface) and photochemistry above the southeastern US with data collected during the SOAS campaign to constrain the model.

The characteristics of urban dust aerosols are of substantial sociopolitical and economic concern. We find that atmospheric dustfall in Xi'an exhibits significant seasonal variations, with a maximum in spring and minimum in autumn. The atmospheric dustfall of Xi'an mainly originates from natural dust sources in East Asia and local anthropogenic sources. Distal natural dust and local anthropogenic dust have different magnetic, morphological, and elemental characteristics.

This article studies the interaction between falling rain and vapour with stable water isotopes. In particular, rain evaporation is relevant for several atmospheric processes, but remains difficult to quantify. A novel framework is introduced to facilitate the interpretation of stable water isotope observations in near-surface vapour and rain. The usefulness of this concept is demonstrated using observations at high time resolution from a cold front. Sensitivities are tested with a simple model.

In this study we analysed ozone changes in the tropical mid-stratosphere as observed by the SCIAMACHY instrument during 2004–2012. We used simulations from TOMCAT model with different chemical and dynamical forcings to reveal primary causes of ozone changes. We also considered measured NO₂ and modelled NO_x, NO_x, and N₂O data. With modelled AoA data we identified seasonal changes in the upwelling speed and explained how those changes affect N₂O chemistry which leads to observed ozone changes.

The use of oxidation flow reactors (OFRs) has been rapidly increasing. We investigate organic peroxy radical (RO₂) chemistry in OFRs by kinetic modeling. It is found that, at low NO, UV intensity should be limited to avoid high radical levels leading to significant reaction of RO₂ with OH and negligible RO₂ isomerization, both of which are atmospherically irrelevant. We also develop two RO₂ fate estimators (for general use and for OFRs) to aid experiment design and interpretation.

Wildfire smoke in July 2015 had a significant impact on air quality, radiation, and energy budgets across British Columbia. With lighter smoke, a wetland and forested site showed enhanced photosynthetic activity (taking in carbon dioxide). However, with dense smoke the forested site became a strong source. These results suggest that smoke during the growing season potentially plays an important role in the carbon budget, and this effect will likely increase as climate changes.

Water-soluble phosphorus (P) in natural and anthropogenic mineral particles in Asian continent outflow is regarded as one of the key nutrients for the biological cycle in the surface seawater of the North Pacific. Our observations at a Chinese coastal site revealed that P solubility was closely relevant to the particle origins, atmospheric acidic processes and ambient relative humidity. The recent severe air pollution over East Asia has likely enhanced bioavailable P input to the North Pacific.

A snow crystal can be generated from an ice nucleating particle or from an ice splinter. In this study we made use of the fact that snow crystals with a particular shape (dendrites) grow within a narrow temperature range (−12 to −17 °C) and can be analysed individually for the presence of an ice nucleating particle. Our direct approach revealed that only one in eight crystals contained such a particle and was of primary origin. The other crystals must have grown from ice splinters.

ACCMIP simulations were used to study NO_y deposition over East Asia in the future. Both dry and wet NO_y deposition show significant decreases in the 2100s under RCP4.5 and RCP8.5 due to large anthropogenic emission reduction. The changes in climate only significantly affect the wet deposition primarily linked to changes in precipitation. Over the coastal seas of China, weaker transport of NO_y from land due to emission reduction infers a larger impact from shipping and lightning emissions.

Over the last few years, many cities in Greece have suffered from significant air quality deterioration events during wintertime. Driven by such observations, we studied the variability and main sources of submicron particulate matter in Athens, Greece, as a large part of the population in this region is exposed to high levels, which sometimes exceed legislative limit values. It was found that such events are mostly associated with combustion sources used for domestic heating during winter.

To shed more light upon the changes in stratospheric circulation in the 21st century, climate projection simulations of 10 state-of-the-art global climate models, spanning from 1960 to 2100, are analyzed. The study shows that in addition to changes in transport, mixing also plays an important role in stratospheric circulation and that the properties of mixing vary over time. Furthermore, the influence of mixing is quantified and a dynamical framework is provided to understand the changes.

Earlier studies showed organic hygroscopicity increases with oxidation level. Such increases have been attributed to higher water solubility for more oxidized organics. By systematically varying the water content of activating droplets, we show that for secondary organic aerosols, essentially all organics are dissolved at the point of droplet activation. Therefore, the organic hygroscopicity is not limited by solubility but is dictated mainly by the molecular weight of organic species.

Polar stratospheric clouds are important for stratospheric chemistry and ozone depletion. Here we statistically compare ground-based and satellite-borne lidar measurements at McMurdo (Antarctica) in order to better understand the differences between ground-based and satellite-borne observations. The satellite observations have also been compared to models used in CCMVAL-2 and CCMI studies, with the goal of testing different diagnostic methods for comparing observations with model outputs.

The ability of positive matrix factorization (PMF) factor analysis to identify and quantify the organic aerosol (OA) sources accurately is tested in this modeling study. The estimated uncertainty of the contribution of fresh biomass burning is less than 30 % and of the other primary sources is less than 40 %, when these sources contribute more than 20 % to the OA. Τhe first oxygenated OA factor includes mainly highly aged OA, while the second oxygenated OA factor contains fresher secondary OA.

In this study, we presented a time series analysis of a 36-year composite CO₂ measurement record at Mount Zugspitze in Germany. Compared with other GAW observatories, Zugspitze proves to be a highly suitable site for monitoring the background levels of air components using proper data selection procedures. Detailed analyses of long-term trends and seasonality, as well as a thorough study of combined weekly periodicity and diurnal cycles, were conducted.

Wildfires in the western US are occurring more frequently and burning larger land areas. Smoke from these fires will play a greater role in regional air quality and atmospheric chemistry than in the past. To help fire and climate modelers and atmospheric experimentalists better understand how smoke impacts the environment, we have separated, identified, classified, and quantified the thousands of organic compounds found in smoke and related their amounts emitted to fire conditions.

Ice nucleating particles (INPs) are atmospheric particles that catalyse the formation of ice crystals in clouds. INPs influence the Earth's radiative balance and hydrological cycle. In this study we measured the concentrations of INPs in the Canadian Arctic marine boundary layer. Average INP concentrations fell within the range measured in other marine boundary layer locations. We also found that mineral dust is a more important contributor to the INP population than sea spray aerosol.

During the heavy pollution process, there are overestimations regarding the exchange between the atmosphere and surface since the normal calculation of turbulent fluxes includes the impact of sub-mesoscale motion. The intermittent turbulence intensity is closely related to the concentration of PM2.5. The intermittency is weaker over the complex surface condition than over the flat terrain, and urbanization reduces the degree of weakening in turbulent exchange during the heavy pollution process.

The role non-mineral components play in the freezing behavior of atmospheric desert dust is not well known. In this study, we use chemical imaging methods to investigate this for airborne and surface-collected desert dust samples. We find that in most cases the ice nucleation behavior is determined by the dust mineralogical composition. However, volatile organic material can coat active sites and decrease the dust ice nucleation ability, while biological particles can significantly increase it.

This study proposed machine-learning-based models to estimate ground-level particulate matter concentrations using satellite observations and numerical model-derived data. Aerosol optical depth was identified as the most significant for estimating ground-level PM concentrations, followed by wind speed and solar radiation. The results show that the proposed models produced better performance than the existing approaches, particularly in improving on the biases of the process-based models.

Detailed molecular chemical composition of water-soluble organic matter in the Himalayas was characterized by positive electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry for the first time. Many products formed from biogenic volatile organic compounds and biomass-burning-emitted compounds were found in the organic compounds, suggesting the important contribution of these two sources in the Himalayas.

Long-term WRF-LES simulations were performed with a horizontal resolution of 200 m for a period of 49 days during the Perdigão campaign. Simulation results were used to characterize the meteorological conditions and to analyse characteristic flow patterns. It could be shown that thermally driven flows including low-level jets frequently occurred during the observation period. Model results were in very good agreement with observations in spite of the long simulation time.

The largest single source of uncertainty in the climate sensitivity predicted by global climate models is how much low-altitude clouds change as the climate warms. Models predict that the amount of liquid within and the brightness of low-altitude clouds increase in the extratropics with warming. We show that increased fluxes of moisture into extratropical storms in the midlatitudes explain the majority of the observed trend and the modeled increase in liquid water within these storms.

Smoke plumes generated in Canadian fire activities were elevated to the lower stratosphere and transported from North America to Europe. The smoke plumes were observed by three lidar systems in northern France. This study provides a comprehensive characterization for aged smoke aerosols at high altitude using lidar observations. It presents that fire activities on the Earth's surface can be an important contributor of stratospheric aerosols and impact the Earth's radiation budget.

Based on rocket-borne true common volume observations of atomic oxygen, atmospheric band emission (762 nm), and background atmosphere density and temperature, one-step, two-step, and combined mechanisms of O₂(b¹Σg⁺) formation were analyzed. We found new coefficients for the fit function based on self-consistent temperature, atomic oxygen, and volume emission observations. This can be used for atmospheric band volume emission modeling or the estimation of atomic oxygen by known volume emission.

Aerosol samples collected at a remote site in the Amazonian rainforest (ATTO) and an urban site in Manaus, Brazil, were investigated on a single particle basis using a quantitative energy-dispersive electron probe X-ray microanalysis, suggesting the different sources and formation mechanisms of secondary aerosols, i.e., the predominant presence of sulfate at the ATTO site from mostly biogenic emissions and the elevated influences of nitrates from anthropogenic activities at the Manaus site.

Assumptions (ideality and thermodynamic equilibrium) commonly made in 3-dimensional air quality models were reconsidered to evaluate their impacts on secondary organic aerosol (SOA) formation. Non-ideality (short-, medium- and long-range interactions of organics and inorganics) influences SOA concentrations by about 30 % over Europe. If SOA are highly viscous rather than inviscid, hydrophobic SOA concentrations increase by 6 % but can increase by an order of magnitude for volatile compounds.

In this study we show the capabilities of combining different remote sensing systems (microwave radiometer – MWR, Doppler lidar – DL – and elastic lidar – EL) for retrieving a detailed picture of the PBL turbulent features. Concerning EL, in addition to analyzing the influence of noise, we explore the use of different wavelengths, which usually includes EL systems operated in extended networks, like EARLINET, LALINET, MPLNET or SKYNET.

The first detailed observational analysis of the complete diurnal cycle of low-level clouds (LLC) and associated atmospheric processes over southern West Africa is performed using the data gathered within the DACCIWA (Dynamics-Aerosol-Chemistry-Cloud-Interactions in West Africa) ground-based campaign. We find cooling related to the horizontal advection, which occurs in connection with the inflow of cool maritime air mass and a prominent low-level jet, to have the dominant role in LLC formation.

Diffuse light can increase the efficiency of vegetation photosynthesis. Diffuse light results from scattering by either clouds or aerosols in the atmosphere. During the dry season biomass burning (BB) on the edges of the Amazon rainforest contributes significantly to the aerosol burden over the entire region. We show that despite a modest effect of change in light conditions, the overall impact of BB aerosols on the vegetation is still important when indirect climate feedbacks are considered.

The hygroscopic growth function of aerosol particles is derived from Raman lidar, whose dependence on aerosol chemical composition is investigated using data from an aerosol chemical speciation monitor (ACSM) and a hygroscopic tandem differential mobility analyzer (H-TDMA) deployed in China. Two distinct cases were chosen with marked differences in their hygroscopic growth, which was fitted by the Kasten model. The differences were attributed to different amounts of chemical species.

In this work, we found that acrolein, the smallest α,β-unsaturated aldehyde, has the potential to form light-absorbing heterocyclic secondary organic aerosol. In the gaseous phase, acrolein can react with gaseous ammonia, forming 3-picoline. In the liquid phase, the dissolved acrolein can react with ammonium to form higher molecular-weight pyridinium compounds. All the pyridinium compounds can increase the light absorptivity of aerosol particles.

Chemistry responsible for sulfate production in northern China winter haze remains mysterious. We propose a potentially key pathway through the reaction of formaldehyde and sulfur dioxide that has not been accounted for in previous studies. The special atmospheric conditions favor the formation and existence of their complex, hydroxymethanesulfonate (HMS).

Located in the world's third Pole and a remote region connecting the Indian and Eurasian plates, Qomolangma National Nature Preserve is an ideal region to study the long-range transport of atmospheric pollutants. Covering both the pre-Indian summer monsoon and Indian summer monsoon periods, our measurement and modeling results have addressed the need for more specific identification of Hg sources in this area and the importance of international cooperation regarding global mercury controls.

We simulated the peatland fires that burned in Greenland in summer 2017. Using satellite data, we estimated that the total burned area was 2345 ha, the fuel amount consumed 117 kt C and the emissions of BC, OC and BrC 23.5, 731 and 141 t, respectively. About 30 % of the emissions were deposited on snow or ice surfaces. This caused a maximum albedo change of 0.007 and a surface radiative forcing of 0.03–0.04 W m⁻², with local maxima of up to 0.63–0.77 W m⁻². Overall, the fires had a small impact.