We present a comprehensive mean evolution of the tropopause inversion layer in mid-latitudes, an atmospheric feature that is located in the region that separates the well-mixed troposphere and the stably stratified stratosphere. We counter-intuitively find this region, which is expected to stabilise atmospheric flow, to exhibit favourable conditions for turbulent exchange between troposphere and stratosphere. This is an important result concerning the overall assessment of exchange processes.

This paper discusses the personal exposure characteristics and health implication of PM_2.5 and bounded chemical species based on three anthropogenic sources and related populations (domestic fires for women, waste burning for students and motorcycle traffic for drivers) in Abidjan and Cotonou in dry and wet seasons of 2016. This work can be regarded as the first attempt at measuring personal exposure to PM_2.5 and its related health risks in underdeveloped countries of Africa.

A significant warming in the troposphere and cooling in the stratosphere are found in satellite measurements (2002–2017). The newest ERA5 data are first used for analyzing temperature and ozone trends in the UTLS and show the best quality compared to other reanalyses. According to model simulations, the temperature increase in the troposphere and ozone decrease in the NH stratosphere are mainly connected to a surface warming of the ocean and subsequent changes in atmospheric circulation.

Two-way feedback occurs between offshore wind and waves. Using an extensive data set of offshore measurements, we show that the wave roughness affecting the wind is dependent on the alignment between the wind and wave directions. Moreover, we propose a new roughness parameterization that takes into account the dependence on alignment. Using this in numerical models will facilitate a better representation of offshore wind, which is relevant to wind energy and and climate modeling.

It has been observed from satellite-based instruments that ammonia levels strongly increased between 2011 and 2015. We have used the CHIMERE CTM to understand what could explain such an increase. We first focused on meteorological condition variations, and it has been concluded that meteorology did not explain ammonia evolution. Then, we focused on SO₂ and NO_x emission evolution rates to evaluate their influences on ammonia. It appears that theses decreases were the main explanation.

For a better understanding of HCHO pollution and atmospheric chemistry, we evaluated primary and secondary sources of HCHO in the Yangtze River Delta based on HCHO column density from OMPS and combined this with in situ surface measurements. We found that secondary formation contributed most to ambient HCHO over longer timescales, but primary emission could be dominant in the winter. Hence, the usability of total HCHO as a proxy of VOC reactivity depends on the timescale of interest.

Current chemical transport models cannot capture the diurnal and nocturnal variation in atmospheric nitrate, which may be relative to the missing atmospheric chlorine chemistry. In this work, the Community Multiscale Air Quality (CMAQ) model with improved chlorine heterogeneous chemistry is applied to simulate the impact of chlorine chemistry on summer nitrate concentrations in Beijing. The results of this work can improve our understanding of nitrate formation.

This study provides source attribution and characterization of BC in the Beijing urban environment in both winter and summer. For the first time, the physically and chemically based source apportionments are compared to evaluate the primary source contribution and secondary processing of BC-containing particles. A method is proposed to isolate the BC from the transportation sector and coal combustion sources.

Using satellite cloud products we investigate the supercooled liquid-water (SLW) distribution Antarctic-wide for the first time. We demonstrate differences between the monthly evolution of the marine low-level mixed-phase clouds and that of the marine low-level pure SLW clouds. In addition to the temperature and sea ice fraction as factors explaining the low-level liquid-cloud seasonal cycle, ice nuclei emissions from open water may also be driving the mixed-phase cloud monthly evolution.

This work presents the link between the chemical composition and the optical properties of the aerosol emissions of an aircraft turbofan using conventional and alternative fuels. A high organic carbon fraction at low thrusts is linked to high single scattering albedos. The optical properties at cruise conditions are used to evaluate the radiative forcing efficiency of aircraft aerosol emissions, which have a substantial warming effect when emitted over highly reflective surfaces such as snow.

Delhi experiences particulate matter concentrations that are among the highest in the world. We conducted a long-term campaign to make highly time-resolved measurements of submicron particle (PM₁) chemical composition in Delhi. Our dataset illuminates key sources and atmospheric processes that impact Delhi's PM₁ concentrations, with sharp differences among seasons and between day and night. In addition to local sources, Delhi's PM₁ levels are amplified by regional pollution and meteorology.

This paper reviewed the air pollution control policies in China from 2005 to 2017. Then we gave an overall evaluation of the effects of these policies on PM_2.5 pollution improvement in China from the perspective of satellite remote sensing. This paper can provide reference for future policy making of air pollution control in China.

This research is the first attempt to comprehensively evaluate the recent 2+26 strategy for air quality improvement in Beijing. We additionally considered two corresponding pollution episodes with different emission-reduction strategies to comprehensively understand the effects of 2+26 strategy. The findings suggested that red alerts be employed in heavy pollution episodes to intentionally reduce vehicle exhaust, which has become the dominant source for high PM_2.5 concentrations in Beijing.

Saharan dust storms may be observed over the desert using false-colour infrared satellite imagery; in one widely used scheme dust displays characteristic pink colours. Simulating satellite imagery using a dust transport model, we confirm that water vapour is a major control on the apparent colour of dust in the false-colour imagery and that dust displays its deepest colours when it is at a high altitude and when the atmosphere is dry. Water vapour can obscure the presence of low-altitude dust.

Precipitation-based deposition of mercury and other trace metals throughout Alaska provides a significant input of pollutants. Deposition shows significant seasonal and spatial variability, largely driven by precipitation patterns. Annual wet deposition of Hg at all AK collection sites is consistently lower than other monitoring stations throughout the CONUS. Hg showed no clear relationship to other metals, likely due to its highly volatile nature and capability of long-range transport.

This paper presents measurements of aerosol particles at a coastal location. The particles were classified into distinct aerosol types using both microphysical measurements and meteorological information, allowing rapid changes between the aerosol types to be reliably identified. These particles can alter cloud and precipitation processes, and inclusion of the differences between types can improve atmospheric models and remote sensing retrievals in littoral zones.

Urban boundary layer (UBL) affects the physical and chemical processes of the pollutants, and UBL structure can also be altered by pollutants. This paper presents the interactions between air pollution and the UBL structure by using the field data mainly collected from a 325 m meteorology tower, as well as from a Doppler wind lidar, during a severe heavy pollution event that occurred during 1–4 December 2016 in Beijing.

Raindrop size distributions have not been systematically studied over the oceans but are significant for remotely sensing, assimilating, and modeling rain. Here we investigate raindrop populations with new global in situ data, compare them against satellite estimates, and explore a new technique to classify the shapes of these distributions. The results indicate the inadequacy of a commonly assumed shape in some regions and the sizable impact of shape variability on satellite measurements.

Characteristics of static stability (N²) in the tropical tropopause are analyzed using 0.1 km vertical resolution temperature profiles retrieved from COSMIC GNSS-RO. We define the tropopause inversion layer (TIL) by the sharp increase in N² across the cold point tropopause (CPT) and the thickness of the enhanced peak in N² just above the CPT. We investigated the TIL at the intraseasonal to interannual timescales above the Maritime Continent and Pacific Ocean with different land–sea distribution.

This is the first study to evaluate and correct the WATCH WFDEI reanalysis product in a highly polluted urban environment. It gives an important understanding of the uncertainties in reanalysis products in local-scale urban modelling in polluted environments and identifies and corrects the most important variables in hydrological modelling. This is also the first study to examine the effects of haze on the local-scale urban hydrological cycle.

The effect of ship emissions on the regional air quality in the Baltic Sea region was investigated with three regional chemistry transport model systems. The ship influence on air quality is shown to depend on the boundary conditions, meteorological data and aerosol formation and deposition schemes that are used in these models. The study provides a reliable approach for the evaluation of policy options regarding emission regulations for ship traffic in the Baltic Sea.

The carbon greenhouse gases (CO₂, CH₄ and CO) were proven to have a large impact on the global carbon cycle and our climate. To understand the variability of the carbon cycle and predict future climate change scenarios, we need to study the processes that drive the changes of these gases in the atmosphere. We study the sources and sinks of CO₂, CH₄ and CO with a combination of measurements and chemical transport modelling to identify missing, underestimated or overestimated sources in Australia.

Radiative forcing induced by deposition of light-absorbing particles (LAPs) on snow is an important surface forcing. Here, we have used high-resolution WRF-Chem (coupled with online snow–LAP–radiation model) simulations for 2013–2014 to estimate the spatial variation in LAP-induced snow albedo darkening effect in high-mountain Asia. Significant improvement in simulated LAP–snow properties with use of a higher spatial resolution for the same model configuration is illustrated over this region.

Atmospheric OH, HO₂, and RO₂ radicals; OH reactivity; and trace gases measured in the Pearl River Delta in autumn 2014 are used for radical budget analyses. The RO₂ budget suggests that unexplained OH reactivity is due to unmeasured volatile organic compounds. The OH budget points to a missing OH source and that of RO₂ to a missing RO₂ sink at low NO. This could indicate a common, unknown process that converts RO₂ to OH without the involvement of NO, which would reduce ozone production by 30 %.

The atmospheric concentrations of the anthropogenic greenhouse gas methane are predicted to rise in the future. In this paper we investigate how very strong methane concentrations will impact the atmosphere. We analyse two experiments, one with doubled and one with quintupled methane concentrations and focus on the rapid atmospheric changes before the ocean adjusts to the induced forcing. In particular these are changes in temperature, ozone, the hydroxyl radical and stratospheric water vapour.

In this paper we study the influence of the cloud microphysical treatments in high-resolution numerical simulation models on radiation fog events, which are still unsatisfactorily predicted in weather forecasts. Our results showed that the choice of which scheme is used can have a significant impact on the strength and life cycle of the fog.

This study evaluates the suitability of 11 satellite-derived aerosol products in describing the spatio-temporal variations over the world. Our results show similar global patterns among these products but noticeable spatial heterogeneity and numerical differences over land regions. In general, MODIS products perform best at reflecting the spatial distributions and capturing the temporal trends of aerosol. This study help readers select a suitable aerosol dataset for their studies.

We report on results that demonstrate the utility of non-methane hydrocarbons as source/sink identification tracers while providing their mixing ratios around the Arabian Peninsula. By introducing novel data-analysis approaches, we establish a new method for separating associated and non-associated (with liquids) gases. We formulate a relationship between hydrocarbon oxidative pairs that can be used to evaluate the relative abundance of the hydroxyl and chlorine radicals in the troposphere.