Secondary inorganic aerosols have an important contribution to PM_2.5. Based on 3 years of atmospheric observation data, this study systematically analyzed the pollution levels and chemical conversion characteristics of nitrate, sulfate and ammonium in PM_2.5 in Chengdu, southwest China, and analyzed the emission and regional transport characteristics of their gaseous precursors. This conclusion can provide an important reference for the current air pollution control.

Every year, huge plumes of smoke hundreds of miles wide travel over the south Atlantic Ocean from fires in central and southern Africa. These plumes absorb the sun’s energy and warm the climate. We used airborne optical instrumentation to determine how absorbing the smoke was as well as the relative importance of black and brown carbon. We also tested different ways of simulating these properties that could be used in a climate model.

With global warming, water vapour increases in the atmosphere. Water vapour is an important gas because it is a natural greenhouse gas and affects the formation of clouds, rain and snow. How much water vapour increases can vary in different regions of the world. To verify if it increases as expected on a regional scale, we analysed water vapour measurements in Switzerland. We found that water vapour generally increases as expected from temperature changes, except in winter.

Chemical effects on the size-resolved hygroscopicity of urban aerosols were examined based on the KORUS-AQ field campaign data (HTDMA and HR-ToF-AMS). The size-resolved chemical composition data were found to be critical in explaining the size-dependent hygroscopicity, as well as the diurnal variation of κ for small particles. Aerosol mixing state information was associated with the size-resolved chemical composition data to reveal chemical information of different hygroscopicity modes.

We report the liquid–liquid phase separation (LLPS) of organic aerosol consisting of α-pinene- and β-caryophyllene-derived ozonolysis products and commercial organic compounds. As compositional complexity increased from one to two organic species, LLPS occurred over a wider range of average O : C values (increasing from 0.44 to 0.67). These results provide further evidence that LLPS is likely frequent in organic aerosol particles in the troposphere, even in the absence of inorganic salt.

To help satellite retrieval of aerosols and studies of their radiative effects, we demonstrate that daytime aerosol optical depth over low-level clouds is similar to that in neighboring clear skies at the same heights. Based on recent airborne lidar and sun photometer observations above the southeast Atlantic, the mean AOD difference at 532 nm is between 0 and -0.01, when comparing the cloudy and clear sides of cloud edges, with each up to 20 km wide.

Trees exchange with the atmosphere nitrogen oxides and ozone, affecting the tropospheric composition and consequently air quality and ecosystem health. We examined the leaf-level gas exchanges for four typical tree species (pine, maple, oak, aspen) found in northern Michigan, US. The leaves largely absorb the gases, showing little evidence of emission. We measured the uptake rates that can be used to improve model studies of the source and sink processes controlling these gases in forests.

This study shows that if energy efficiency improvements in cooling technologies are addressed simultaneously with a phase-down of hydrofluorocarbons (HFCs), not only will global warming be mitigated through the elimination of HFCs but also by saving about a fifth of future global electricity consumption. This means preventing between 411 and 631 Pg CO2 equivalent of greenhouse gases between today and 2100, thereby offering a significant contribution towards staying well below 2 °C warming.

To estimate the impacts of atmospheric aerosol particles on air quality, knowledge of size distributions of particles emitted from anthropogenic sources is needed. We introduce a new method for determining size-resolved particle number emissions from measured particle size distributions. We apply our method to data measured in Beijing, China. We find that particle number emissions at our site are dominated by emissions of particles smaller than 30 nm, originating mainly from traffic.

We investigate the effects of future land use and land cover change (LULCC) on surface ozone air quality worldwide and find that LULCC can significantly influence ozone in North America and Europe via modifying surface energy balance, boundary-layer meteorology, and regional circulation. The strength of such “biogeophysical effects” of LULCC is strongly dependent on forest type and generally greater than the “biogeochemical effects” via changing deposition and emission fluxes alone.

An accurate estimation of China’s fossil-fuel CO₂ emissions (FFCO₂) is significant for quantification of carbon budget and emissions reductions towards the Paris Agreement goals. Here we assessed 9 global and regional inventories. Our findings highlight the significance of using locally measured coal emission factors. We call on the enhancement of physical measurements for validation and provide comprehensive information for inventory, monitoring, modeling, assimilation, and reducing emissions.

In this study, we highlight the potential impact of particles from certain terrestrial sources on the formation of ice crystals in clouds. In particular, we focus on biogenic particles consisting of various organic compounds, which makes it very difficult to predict the ice nucleation properties of complex ambient particles. We find that these ambient particles are often more ice active than individual components.

We have calculated the effects of air pollution in Europe from shipping on levels of PM_2.5 and ozone and depositions of oxidised nitrogen and sulfur from individual sea areas and from all global shipping. Model results are shown for Europe as a whole but also focusing on select, mainly coastal, countries. Calculations are made using 2017 emissions supplemented by calculations reducing sulfur emissions from ships by about 80 % following the implementation of the 2020 global sulfur cap.

Surface summer ozone increased in China from 2013 to 2019 despite new governmental efforts targeting ozone pollution. We find that the ozone increase is mostly due to anthropogenic drivers, although meteorology also plays a role. Further analysis for the North China Plain shows that PM_2.5 continued to decrease through 2019, while emissions of volatile organic compounds (VOCs) stayed flat. This could explain the anthropogenic increase in ozone, as PM_2.5 scavenges the radical precursors of ozone.

The observation data from a receptor site in the Pearl River Delta region were analyzed by a photochemical box model with near-explicit chemical mechanisms (i.e., the Master Chemical Mechanism, MCM), improvements with reversible and irreversible heterogeneous processes of glyoxal and methylglyoxal, and the gas-particle partitioning of oxidation products in the present study.

In 2016, a scientific research flight above Scandinavia acquired various atmospheric data (temperature, gas composition, etc.). Through advanced 3-D reconstruction methods, a superposition of multiple gravity waves was identified. An in-depth analysis enabled the characterisation of these waves as well as the identification of their sources. This work will enable a better understanding of atmosphere dynamics and could lead to improved climate projections.

In the southeast Atlantic, well-defined smoke plumes from Africa advect over marine boundary layer cloud decks; both are most extensive around September, when most of the smoke resides in the free troposphere. A framework is put forth for evaluating the performance of a range of global and regional atmospheric composition models against observations made during the NASA ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) airborne mission in September 2016.

Severe spring haze and influences of long-range transport in the Seoul metropolitan area (SMA) in March 2019 were investigated. Simultaneous downwind (SMA) and upwind (Beijing) measurements using AMS and ACSM over the same period showed that PM species can be transported in approximately 2 d. Nitrate was the most responsible, and sulfate and two regional-transport-influenced SOAs also contributed. Enhancement of Pb also showed that the haze in the SMA was influenced by the regional transport.

This article details new field observations of the nitrogen stable isotopic composition of ammonia emitted from vehicles conducted in the US and China. Vehicle emissions of ammonia may be a significant source to urban regions with important human health and environmental implications. Our measurements have indicated a consistent isotopic signature from vehicle ammonia emissions. The nitrogen isotopic composition of ammonia may be a useful tool for tracking vehicle emissions.

Rossby wave packet (RWP) dynamics are crucial for weather forecasting, climate change projections and stratosphere–troposphere interactions. Our study is a first attempt to describe RWP behavior in the UTLS with global coverage directly from observations, using GNSS-RO data. Our novel results show an interesting relation of RWP vertical propagation with sudden stratospheric warmings and provide very useful information to improve RWP diagnostics in models and reanalysis.

High viscosity organic particles (HVOPs) in the Southern Great Plains have been analyzed, and two particle types were found. Previously studied tar balls and the recently discovered airborne soil organic particles (ASOPs) are both shown to be brown carbon (BrC). These particle types can be identified in bulk by an absorption Ångström exponent approaching 2.6. HVOP types can be differentiated by comparing carbon absorption spectrum peak ratios between the carboxylic acid, alcohol, and sp² peaks.

We quantify differences in surface-level fine particle mass (PM_2.5) chemical composition in relation to satellite-derived cloud flags and find significant differences between clear-sky and cloud days. The work suggests that future analysis in this area is warranted.

A month-long set of summertime measurements in a remote area in the Mediterranean is used to quantify aerosol absorption. The measured light absorption was two or more times higher than that of fresh black carbon. The absorption enhancement due to the coating of black carbon cores by other aerosol components could explain only part of this absorption enhancement. The rest was due to brown carbon, mostly in the form of extremely low volatility organic compounds.

In this study, we present an improved cloud model that reproduces the behaviour of mixed-phase clouds containing liquid droplets and ice crystals in more detail than before. This model is a convenient computational tool that enables the study of phenomena that cannot fit into a laboratory. These clouds have a significant role in climate, but they are not yet properly understood. Here, we show the advantages of the new model in a case study focusing on Arctic mixed-phase clouds.