Recent measurements show some evidence that the amplitudes of atmospheric gravity waves (horizontal wavelengths of 100–2000 km), which propagate from the troposphere (0–10 km) to the stratosphere and mesosphere (10–100 km), increase more strongly with height during daytime than during nighttime. This study shows that ozone–temperature coupling in the upper stratosphere can principally produce such an amplification. The results will help to improve atmospheric circulation models.

Effects of urban aerosol pollution in Moscow were analyzed using the COSMO-ART chemical transport model and intensive measurement campaigns. We show that urban aerosol comprises about 15–20% of columnar aerosol content, consisting mainly of fine aerosol mode. The black carbon (BC) fraction is about 5 %, depending on particle dispersion intensity (IPD). The BC fraction low value explains weak absorbing properties of the Moscow atmosphere. IPD also defines the daily cycle of urban aerosol species.

We present a new method to derive global information of the hydroxyl radical (OH), an important atmospheric oxidant. OH controls the lifetime of trace gases important to air quality and climate. We use satellite observations of ozone, carbon monoxide, methane and water vapour in a simple expression to derive OH around 3–4 km altitude. The derived OH compares well to model and aircraft OH data. We then apply the method to 10 years of satellite data to study the inter-annual variability of OH.

Ozone formation is enhanced by higher OH concentration and higher temperature but is influenced little by SO₂. SO₂ can largely enhance the particle formation. Organo-sulfates and organo-nitrates are detected in the formed particles, and the presence of SO₂ can promote the formation of organo-sulfates. The results provide a scientific basis for systematically evaluating the effects of SO₂, OH concentration, and temperature on the oxidation of mixed organic gases in the atmosphere.

The sources of ice-nucleating particles (INPs) are poorly understood in the Southern Hemisphere (SH). We studied INPs in the boundary layer in the southern Patagonia region. No seasonal cycle of INP concentrations was observed. The majority of INPs are biogenic particles, likely from local continental sources. The INP concentrations are higher when strong precipitation occurs. While previous studies focused on marine INP sources in SH, we point out the importance of continental sources of INPs.

This study explores how increased aerosol particles impact tropical sea breeze cloud systems under different environments and how a range of environments modulate these cloud responses. Overall, sea breeze flows and clouds that develop therein become weaker due to interactions between aerosols, sunlight, and land surface. In addition, surface rainfall also decreases with more aerosol particles. Weakening of cloud and rain with more aerosols is found irrespective of 130 different environments.

Evaluating impacts of emission changes on air quality requires accounting for meteorological variability. Many studies use simple regression methods to correct for meteorology, but little is known about their performance. Using cases in the US and China, we show that widely used regression models do not perform well and can lead to biased estimates of emission-driven trends. We propose a novel machine learning method with lower bias and provide recommendations to policymakers and researchers.

High-time-resolution measurements of volatile organic compounds (VOCs) were made using an online mass spectrometer at a 600 m tall tower in urban region. Compositions, temporal variations, and sources of VOCs were quantitatively investigated in this study. We find that VOC measurements in urban regions aloft could better characterize source characteristics of anthropogenic emissions. Our results could provide important implications in making future strategies for control of VOCs.

Previous studies generally ignored the faint aerosols undetected by the CALIPSO layer detection algorithm because they are too optically thin. Here, we retrieved the faint aerosol extinction based on instantaneous CALIPSO observations with the constraint of SAGE data. The correlation and normalized root-mean-square error of the retrievals with independent SAGE data are 0.66 and 100.6 %, respectively. The minimum retrieved extinction at night can be extended to 10^-4 km^-1 with 125 % uncertainty.

In this study, we analyse trends of total column water vapour (TCWV) using multiple years of satellite observations and find, on the global average, an increase in the TCWV amount by about 0.21 % per year. Further investigations of the hydrological cycle reveal that the assumption of temporally invariant relative humidity is not always fulfilled and that the response of the global water vapour turnover time to global warming is 2 to 3 times higher than previously reported values.

This study quantified the contribution of each urban-induced meteorological effect (temperature, humidity, and circulation) to aerosol concentration. We found that the urban heat island (UHI) circulation dominates the UHI effects on aerosol. The UHI circulation transports aerosol and its precursor gases from the warmer lower boundary layer to the colder lower free troposphere and promotes the secondary formation of ammonium nitrate aerosol in the cold atmosphere.

Chemical transport models forced with (re)analysis meteorological fields are ideally suited for interpreting the influence of important physical processes on the ozone variability. We use TOMCAT forced by ECMWF ERA-Interim and ERA5 reanalysis data sets to investigate the effects of reanalysis forcing fields on ozone changes. Our results show that models forced by ERA5 reanalyses may not yet be capable of reproducing observed changes in stratospheric ozone, particularly in the lower stratosphere.

Atmospheric impacts of chlorinated very short-lived substances (Cl-VSLS) over the first two decades of the 21st century are assessed using the UM-UKCA chemistry–climate model. Stratospheric input of Cl from Cl-VSLS is estimated at ~130 ppt in 2019. The use of model set-up with constrained meteorology significantly increases the abundance of Cl-VSLS in the lower stratosphere relative to the free-running set-up. The growth in Cl-VSLS emissions significantly impacted recent HCl and COCl₂ trends.

A modelling system for meteorology and chemistry transport processes, WRF–CHIMERE, has been tested and validated for three East African conurbations using the most up-to-date anthropogenic emissions available. Results show that the model is able to reproduce hourly and daily temporal variabilities in aerosol concentrations that are close to observations in both urban and rural environments, encouraging the adoption of numerical modelling as a tool for air quality management in East Africa.

Our study explored the synergy of combined column and surface measurements during GMAP (GEMS Map of Air Pollution) campaign. It has several points to note for vertical distribution analysis. Particularly under prevailing local wind meteorological conditions, Pandora-based vertical structures sometimes showed negative correlations between column and surface measurements. Vertical analysis should be done carefully in some local meteorological conditions when employing either surface or columns.

Understanding regional greenhouse gas emissions into the atmosphere is a prerequisite to mitigate climate change. In this study, we investigated the regional contributions of carbon dioxide (CO₂) at the location of the high Alpine observatory Jungfraujoch (JFJ, Switzerland, 3580 m a.s.l.). To this purpose, we combined receptor-oriented atmospheric transport simulations for CO₂ concentration in the period 2009–2017 with stable carbon isotope (δ¹³C–CO₂) information.

A record-breaking severe O₃ pollution episode occurred under the influence of a Pacific subtropical high followed by Typhoon Mitag in the Pearl River Delta (PRD) in early Autumn 2019. Through WRF-CMAQ model simulations, we propose that the enhanced photochemical production of O₃ during the episode is a major cause of the most severe O₃ pollution year since the official O₃ observation started in the PRD in 2006.

We developed a Bayesian atmospheric inversion system based on the 4D local ensemble transform Kalman filter (4D-LETKF) algorithm coupled with GEOS-Chem from the latest Orbiting Carbon Observatory-2 (OCO-2) V10r XCO₂ retrievals. This is the first adaptation of 4D-LETKF to an OCO-2-based global carbon inversion system. We inferred global gridded carbon fluxes and investigated their magnitudes, variations, and partitioning schemes to understand the global and regional carbon budgets for 2015–2020.

Extensive stratocumulus clouds over the south-eastern Atlantic (SEA) can lead to a cooling effect on the climate. A key pathway by which aerosols affect cloud properties is by acting as cloud condensation nuclei (CCN). Here, we investigated the source attribution of CCN in the SEA as well as the cloud responses. Our results show that aerosol nucleation contributes most to CCN in the marine boundary layer. In terms of emissions, anthropogenic sources contribute most to the CCN and cloud droplets.

We quantify methane emissions in China and contributions from different sectors by inverse analysis of 2019 TROPOMI satellite observations of atmospheric methane. We find that anthropogenic methane emissions for China are underestimated in the national inventory. Our estimate of emissions indicates a small life-cycle loss rate, implying net climate benefits from the current coal-to-gas energy transition in China. However, this small loss rate can be misleading given China's high gas imports.

We presented yields and compositions of Si-containing SOAs generated from the reaction of cVMSs (D3–D6) with OH radicals. NO_x played a negative role in cVMS SOA formation, while ammonium sulfate seeds enhanced D3–D5 SOA yields at short photochemical ages under high-NO_x conditions. The aerosol mass spectra confirmed that the components of cVMS SOAs significantly relied on OH exposure. A global cVMS-derived SOA source strength was estimated in order to understand SOA formation potentials of cVMSs.

The relevance of microphysical and land-surface uncertainties for convective-scale predictability is evaluated with a combined-perturbation strategy in realistic convection-resolving simulations. We find a large ensemble spread which demonstrates that the uncertainties investigated here and, in particular, their collective effect are highly relevant for quantitative precipitation forecasting of summertime convection in central Europe.

Black carbon is the second strongest absorbing component in the atmosphere that exerts warming effects on climate. One critical challenge in quantifying the ambient black carbon's radiative effects is addressing the BC microphysical properties. In this study, the microphysical properties of the aged and fresh BC particles are synthetically analyzed under different atmospheres. The measurement results can be further used in models to help constrain the uncertainties of the BC radiative effects.

TROPOMI measurements offer a valuable means to validate emissions inventories and ozone formation regimes, with important limitations. Lightning NO_x is important to account for in Texas and can contribute up to 24 % of the column NO₂ in rural areas and 8 % in urban areas. Modeled NO₂ in urban areas agrees with TROPOMI NO₂ to within 20 % in most circumstances, with a small underestimate in Dallas (−13 %) and Houston (−20 %). Near Texas power plants, the satellite appears to underrepresent NO₂.

In this work we use a combination of observational data from an aircraft campaign and model results to investigate the effect of the European lockdown due to COVID-19 in spring 2020. Using model results, we show that the largest relative changes to the atmospheric composition caused by the reduced emissions are located in the upper troposphere around aircraft cruise altitude, while the largest absolute changes are present at the surface.

Aircraft condensation trails (contrails) contribute to over half of the climate forcing attributable to aviation. This study uses historical air traffic and weather data to simulate contrails in the North Atlantic over 5 years, from 2016 to 2021. We found large intra- and inter-year variability in contrail radiative forcing and observed a 66 % reduction due to COVID-19. Most warming contrails predominantly result from night-time flights in winter.

California’s ozone persistently exceeds the air quality standards. We studied the spatial distribution of volatile organic compounds (VOCs) that produce ozone over the most polluted regions in California using aircraft measurements. We find that the oxygenated VOCs have the highest ozone formation potential. Spatially, biogenic VOCs are important during high ozone episodes in the South Coast Air Basin, while dairy emissions may be critical for ozone production in San Joaquin Valley.

The nitrate phase state can play a critical role in determining the occurrence and extent of nitrate depletion in internally mixed NaNO3–DCA particles, which may be instructive for relevant aerosol reaction systems. Besides, organic acids have a potential to deplete nitrate based on the comprehensive consideration of acidity, particle-phase state, droplet water activity, and HNO₃ gas-phase diffusion.

Aerosols and clouds persist as the dominant sources of uncertainty in climate projections. In this modelling study, we investigate the role of marine aerosols in influencing the lifetime of low-level clouds. Our high resolution simulations show that sea spray can both extend and shorten the lifetime of the cloud layer depending on the model setup. The impact of the primary marine organics is relatively limited while secondary aerosol from monoterpenes can have larger impact.

The first 10-year data record (2008–2017) of HNO₃ total columns measured by the IASI-A/MetOp infrared sounder is exploited to monitor the relationship between the temperature decrease and the HNO₃ loss observed each year in the Antarctic stratosphere during the polar night. We verify the recurrence of specific regimes in the cycle of IASI HNO₃ and identify the day and the 50 hPa temperature (drop temperature) corresponding to the onset of denitrification in Antarctic winter for each year.