Global models of tropospheric chemistry and transport show a persistent diversity in results that has not been fully explained. We demonstrate the first use of global sensitivity analysis consistently across three independent models to explore these differences and reveal both clear similarities and surprising differences which have important implications for our assessment of future atmospheric composition change.

In situ measurements of a free-tropospheric (FT) biomass burning aerosol plume in contact with the boundary layer inversion overriding a pocket of open cells (POC) and surrounding stratiform cloud are presented. The data highlight the contrasting thermodynamic, aerosol and cloud properties in the two cloud regimes and further demonstrate that the cloud regime plays a key role in regulating the flow of FT aerosols into the boundary layer, which has implications for the aerosol indirect effect.

Incomplete understanding of how aerosol affects clouds degrades our ability to predict future climate. In particular, it is unclear how aerosol affects the lifetime of clouds. Does it increase or decrease it? This confusion is partially because causality flows from aerosol to clouds and clouds to aerosol, and it is hard to tell what is happening in observations. Here, we use simulations to tell us about how clouds affect aerosol and use this to interpret observations, showing increased lifetime.

In this paper we summarize observations of short-lived halocarbons in the tropopause region. We show that, especially during winter, the levels of short-lived bromine gases at the extratropical tropopause are higher than at the tropical tropopause. We discuss the impact of the distributions on stratospheric bromine levels and compare our observations to two models with four different emission scenarios.

Low ozone and low water vapour signatures in the UTLS were investigated using balloon-borne measurements and trajectory calculations. The results show that deep convection in tropical cyclones over the western Pacific transports boundary air parcels with low ozone into the tropopause region. Subsequently, these air parcels are dehydrated when passing the lowest temperature region (< 190 K) during quasi-horizontal advection.

A vast area in China is currently going through severe haze episodes with drastically elevated concentrations of PM_2.5 in winter. Nitrate and sulfate are main constituents of PM_2.5, but their formations via NO₂ and SO₂ oxidation are still not comprehensively understood. Our results found that the gas-phase reaction of NO₂ with OH and the heterogeneous hydrolysis of N₂O₅ play key roles in nitrate formation, and SO₂ aqueous-phase oxidation with H₂O₂ rather than NO₂ contributed greatly to sulfate.

Thin (~ 100 m) supercooled liquid water (SLW, water staying in liquid phase below 0 °C) clouds have been detected, analysed, and modelled over the Dome C (Concordia, Antarctica) station during the austral summer 2018–2019 using observations and meteorological analyses. The SLW clouds were observed at the top of the planetary boundary layer and the SLW content was always strongly underestimated by the model indicating an incorrect simulation of the surface energy budget of the Antarctic Plateau.

Atmospheric aerosols in Antarctica contribute to regulate the delicate budget of cloud formation and precipitations. Besides the well-known biogenic production of sulfur-containing aerosol components such as methanesulfonate (MSA), the assessment of biological sources of organic particles in Antarctica remains an active area of research. Here we present the results of aerosol organic characterization during a research cruise performed in the Weddell Sea and in the Southern Ocean in Jan–Feb 2015.

Soot particles released during anthropogenic activities may lead to positive direct or negative indirect climate forcing depending on their aging in the atmosphere. The latter occurs whenever soot particles act as cloud condensation nuclei (CCN) and trigger the formation of persistent clouds. Herein, we investigate the impact of the size distribution and morphology of freshly emitted soot particles on their aging process and propose a model to quantitatively predict their efficiency as CCN.

Ozone is an important pollutant with impacts on health and the environment. Ozone is lost to plants, land and the oceans. Loss to the ocean is slow compared to all other types of land cover and has not received as much attention. We build on previous work to more accurately model ozone loss to the ocean. We find changes in the concentration of ozone over the oceans, notably the Southern Ocean, which improves model performance.

This report describes a simple, safe and effective method to prepare nitrate esters of terpenes (carene, limonene, perillic alcohol, beta-pinene and alpha-pinene) which are key oxidation products in the atmosphere. These compounds are implicated in the formation of secondary organic aerosols. A compilation of the relevant spectroscopic data has been presented. The availability of these compounds and their characterization data will enable further study of the structure–reactivity relationships.

Given their critical impact on radiative forcing, sulfate aerosols have been extensively studied using their isotope signatures (δ³⁴S, ∆³³S, ∆³⁶S, δ¹⁸O, and ∆¹⁷O). A striking observation is that ∆³³S > 0 ‰, implying a missing reservoir in the sulfur cycle. Here, we measured ∆³³S < 0 ‰ in black crust sulfates (i.e., formed on carbonate walls) that must therefore result from distinct chemical pathway(s) compared to sulfate aerosols, and they may well represent this complementary reservoir.

We estimated the ammonia emissions based on the constant emission factors and those characterizing the agricultural processes for the Yangtze River Delta, China. The discrepancies between the two estimates and their causes were analyzed. Based on ground and satellite observations, the two estimates were evaluated with air quality modeling. This work indicates ways to improve the emission estimation and helps better understand the necessity of multi-pollutant control strategy.

Major carbonaceous aerosol species were apportioned among FF combustion, BB and biogenic sources in various types of atmospheric environments of interest in the Carpathian Basin in different months representing different seasons. The conclusions present novel and valuable research contributions on a large area in central Europe.

This research work investigates organic aerosol formation in California during the CalNex study. We update the chemical transport model with the most recent mobile-source emission data and introduce a simple parameterization for secondary organic aerosol formed from intermediate-volatility organic compounds. Our results highlight the important contribution of IVOCs to SOA production in the Los Angeles region but underscore that other uncertainties must be addressed to close the SOA mass balance.

Residential wood combustion can cause substantial emissions of fine particulate matter and adverse health effects. This study has, for the first time, evaluated the impacts of residential wood combustion in a harmonised manner in four Nordic cities. Wood combustion caused major shares of fine particle concentrations in Oslo (up to 60 %) and Umeå (up to 30 %) and also notable shares in Copenhagen (up to 20 %) and Helsinki (up to 15 %).

This study provides a holistic picture of N₂O₅ heterogeneous uptake on ambient aerosols and the influencing factors under various climatic and chemical conditions in China, and it proposes an observation-based empirical parameterization. The empirical parameterization can be used in air quality models to improve the prediction of PM_2.5 and photochemical pollution in China and similar polluted regions of the world.

There is a great need to define health-affecting pollution by small particles as “respirable aerosol”. The wintertime San Joaquin Valley experiences severe episodes that need full maps. A few air pollution monitors are set out by agencies in such regions. Satellite data on haziness and daily calibration using the monitors map out improved pollution estimates for the winter of 2012–2013. These show patterns of valuable empirical information about sources, transport, and cleanout of pollution.

A regional fully coupled meteorology–chemistry model, Weather Research and Forecasting model with Chemistry (WRF-Chem), was employed to study the seasonality of ozone (O₃) pollution and its sources in both China and India.

This study uses 1 min radiation and lidar measurements at three stations over the Tibetan Plateau (TP) to parametrize downward longwave radiation (DLR) during summer months. Clear-sky DLR can be estimated from the best parametrization with a RMSE of 3.8 W m^-2 and R² > 0.98. Additionally cloud base height under overcast conditions is shown to play an important role in cloudy DLR parametrization, which is considered in the locally calibrated parametrization over the TP for the first time.

In this paper we present the variability in cirrus cloud properties using a Polly^XT Raman lidar over high and tropical latitudes. The kind of information presented here can be rather useful in the cirrus parameterisations required as input to radiative transfer models and can be a complementary tool for satellite products that cannot provide cloud vertical structure.

We present a statistical cluster analysis of the physical characteristics of particle size distributions collected at Halley (Antarctica) for the year 2015. Complex interactions between multiple ecosystems, coupled with different atmospheric circulation, result in very different aerosol size distributions populating the Southern Hemisphere.

We investigated the effect of SO₂ under different humidities on optical properties of toluene-derived SOA under four conditions with CRDs and PAX at 532 and 375 nm, respectively. Our results showed that SO₂ under different humidities can change the refractive complex index of toluene SOA by influencing the multiphase processes and altering the aerosol chemical compositions. Different atmospheric conditions could affect the properties of toluene SOA, as well as the global radiative balance.

The paper presents an evaluation of the CAMS global reanalysis of reactive gases performed for the period 2003–2016. The evaluation is performed by comparing concentrations of chemical species gathered during airborne field campaigns with calculated values. The reanalysis successfully reproduces the observed concentrations of ozone and carbon monoxide but generally underestimates the abundance of hydrocarbons. Large discrepancies exist for fast-reacting radicals such as OH and HO₂.

In order to better understand the physical processes behind aerosol effects on the atmospheric energy budget, we analyse numerical simulations of tropical cloud systems. Two sets of simulations, at different dates during the NARVAL 2 field campaign, are simulated with different dominant cloud modes. Our results demonstrate that under different environmental conditions, the response of the atmospheric energy budget to aerosol perturbation could be different.

An accurate independent verification methodology to estimate methane (a powerful greenhouse gas) emissions is essential for the effective implementation of policies that aim to reduce the impacts of climate change. In this paper, four uncertainties that complicate the independent estimation of urban methane emissions are identified: the definition of urban domain, background heterogeneity, emissions temporal variability, and missing sources. Ways to improve emission estimates are suggested.