Cloud phase has been found to significantly impact cloud thermodynamics and Earth’s radiation budget, and various factors influence it. This study investigates the sensitivity of the cloud-phase distribution to the ice-nucleating particle concentration and thermodynamics. Multiple simulation experiments were performed using the ICON model at the convection-permitting resolution of 1.2 km. Simulation results were compared to two different retrieval products based on SEVIRI measurements.

For the first time, rather clear evidence is found that wildfire smoke particles can trigger strong cirrus formation. This finding is of importance because intensive and large wildfires may occur increasingly often in the future as climate change proceeds. Based on lidar observations in Cyprus in autumn 2020, we provide detailed insight into the cirrus formation at the tropopause in the presence of aged wildfire smoke (here, 8–9 day old Californian wildfire smoke).

In this work, we focus on the atmospheric chemistry and consequences for air quality of 2-methylpentanal (2MP), which is widely used as a flavoring ingredient and as an intermediate in the synthesis of dyes, resins, and pharmaceuticals. Measurements are presented on how fast 2MP is degraded by sunlight and oxidants like hydroxyl (OH) radicals and chlorine (Cl) atoms and what products are generated. We conclude that 2MP will be degraded in a few hours, affecting local air quality.

In this study, we used a regional chemical transport model to characterize the different parameters of atmospheric oxidative capacity in recent chemical environments in China. These parameters include the production and destruction rates of ozone and other oxidants, the ozone production efficiency, the OH reactivity, and the length of the reaction chain responsible for the formation of ozone and RO_x. They are also affected by the aerosol burden in the atmosphere.

The effectiveness of climate change mitigation needs to be scrutinized by monitoring greenhouse gas (GHG) emissions. Countries report their emissions to the UN in a bottom-up manner. By combining atmospheric observations and transport models someone can independently validate emission estimates in a top-down fashion. We report Swiss emissions of synthetic GHGs based on kilometer-scale transport and inverse modeling, highlighting the role of appropriate resolution in complex terrain.

Atmospheric water vapor plays an essential role in the global energy balance, hydrological cycle, and climate system. This paper characterizes and compares the global, latitudinal, and regional variabilities of COSMIC and ERA5 water vapor distribution, as well as the seasonality and long-term trends at selected pressure levels from 2007 to 2018. Evaluation of spatiotemporal variabilities of atmospheric water vapor ensures the qualities of COSMIC and reanalysis water vapor for climate studies.

Polarimetric radar observations were assimilated for the first time in a convective-scale numerical weather prediction system in Germany and their impact on short-term precipitation forecasts was evaluated. The assimilation was performed using microphysical retrievals of liquid and ice water content and yielded slightly improved deterministic 9 h precipitation forecasts for three intense summer precipitation cases with respect to the assimilation of radar reflectivity alone.

Tropical deep convective clouds, and the thin cirrus (ice) clouds that flow out from them, are important for modulating the energy budget of the tropical atmosphere. This work uses a new method to track the evolution of the properties of these clouds across their entire lifetimes. We find these clouds cool the atmosphere in the first 6 h before switching to a warming regime after the deep convective core has dissipated, which is sustained beyond 120 h from the initial convective event.

Poor air quality caused by high concentrations of particulate matter is one of the most severe public health concerns for humans worldwide. One of the most important biological mechanisms inducing adverse health effects is the oxidant–antioxidant imbalance. We showed that the oxidative stress changed substantially and in a complex manner with location and season. Biomass burning exhibited the dominant influence, while motor vehicles played an important role in the non-heating period.

The annual cycle of dust and anthropogenic aerosols' vertical distributions was revealed by polarization Raman lidar in Beijing. Anthropogenic aerosols typically accumulate at the top of the mixing layer (ML) due to the hygroscopic growth of atmospheric particles, and this is most significant in summer. There is no significant relationship between bottom dust mass concentration and ML height, while the dust in the upper air tends to be distributed near the mixing layer.

This paper evaluates measurements of cloud drop size distributions made from airplanes. We find that as the number of cloud drops increases the distribution of the cloud drop sizes narrows. The data are used to develop a simple equation that relates the drop number to the width of the drop sizes. We then use this equation to demonstrate that existing approaches to observe the drop number from satellites contain errors that can be corrected by including the new relationship.

D₅ is an emerging anthropogenic pollutant that is ubiquitous in indoor and urban environments, and the OH oxidation of D₅ forms secondary organosiloxane aerosol (SOSiA). Application of a kinetic box model that uses a volatility basis set (VBS) showed that consideration of oxidative aging (aging-VBS) predicts SOSiA formation much better than using a standard-VBS model. Ageing-dependent parameterization is needed to accurately model SOSiA to assess the implications of siloxanes for air quality.

We develop a modeling framework using the Weather Research and Forecasting model at a high spatial resolution (up to 400 m) to simulate atmospheric transport of greenhouse gases and interpret column observations. Output is validated against weather stations and column measurements in August 2018. The differential column method is applied, aided by air-mass transport tracing with the Stochastic Time-Inverted Lagrangian Transport (STILT) model, also for an exploratory measurement interpretation.

This study provides ground-observational evidence that supports earlier suggestions that savanna fires are the main emitters and modulators of carbon monoxide gas in Africa. Using isotope-based techniques, the study has shown that about two-thirds of this gas is emitted from savanna fires, while for urban areas, in this case Nairobi, primary sources approach 100 %. The latter has implications for air quality policy, suggesting primary emissions such as traffic should be targeted.

Surface PM_2.5 concentrations can be enhanced by aerosol–radiation interactions (ARIs) and aerosol–cloud interactions (ACIs). In this study, we found  PM_2.5 enhancement induced by ACIs shows a significantly smaller decrease ratio than that induced by ARIs in China with anthropogenic emission reduction from 2013 to 2021, making ACIs more important for enhancing PM_2.5 concentrations. ACI-induced PM_2.5 enhancement needs to be emphatically considered to meet the national PM_2.5 air quality standard.

A long-term record of satellite observations is used to study extreme water vapor concentrations in the lower stratosphere, which are important to climate variability and change. We use a deeper layer of stratospheric observations than prior work to more comprehensively identify these events. We show that extreme water vapor concentrations are frequent, especially in the lowest layers of the stratosphere that have not been analyzed previously.

Measurements of OH, HO₂ and RO₂ radicals and also OH reactivity were made at a UK coastal site and compared to calculations from a constrained box model utilising the Master Chemical Mechanism. The model agreement displayed a strong dependence on the NO concentration. An experimental budget analysis for OH, HO₂, RO₂ and total RO_x demonstrated significant imbalances between HO₂ and RO₂ production rates. Ozone production rates were calculated from measured radicals and compared to modelled values.

In this study, we present the partitioning of CO₂ signals from biogenic, petroleum and natural gas sources by combining CO, ¹³CO₂ and ¹⁴CO₂ measurements. Using measurements from flask air samples at three sites in the greater Los Angeles region, we find larger and positive contributions of biogenic signals in winter and smaller and negative contributions in summer. The largest contribution of natural gas combustion generally occurs in summer.

This study characterized the optical properties of light-absorbing organic compounds, called brown carbon (BrC), in atmospheric cloud water samples. In all samples, light absorption by BrC increased linearly with increasing pH. There was variability in the sensitivity of the absorption–pH relationship, depending on the degree of influence from fire emissions. Overall, these results show that the climate forcing of BrC is quite strongly affected by its pH-dependent absorption.

Accurate fog forecasting is difficult in a complex environment. Spatial variations in soil moisture could impact fog. Here, we carried out fog simulations with spatially different soil moisture in complex topography. The soil moisture was calculated using satellite observations. The results show that the spatial variations in soil moisture do not have a significant impact on where fog occurs but do impact how long fog lasts. This finding could improve fog forecasts in the future.

This study investigated the effect of COVID-19 lockdown (LCD) measures on the formation and evolutionary process of diacids and related compounds from field observations. Results demonstrate that more aged organic aerosols are observed during the LCD due to the enhanced photochemical oxidation. Our study also found that the reactivity of ¹³C was higher than that of ¹²C in the gaseous photochemical oxidation, leading to higher δ¹³C values of C₂ during the LCD than before the LCD.

Annual PM_2.5 emissions in China consistently decreased by about 3% to 5% from 2017 to 2020 with spatial variations and seasonal dependencies. High-temporal-resolution and dynamics-based PM_2.5 emission estimates provide quantitative diurnal variations for each season. Significant reductions in PM_2.5 emissions in the North China Plain and northeast of China in 2020 were caused by COVID-19.

An important Arctic climate process is the release of heat fluxes from sea ice openings to the atmosphere that influence the clouds. The characterization of this process is the objective of this study. Using synergistic observations from the MOSAiC expedition, we found that single-layer cloud properties show significant differences when clouds are coupled or decoupled to the water vapour transport which is used as physical link between the upwind sea ice openings and the cloud under observation.

We conducted burning experiments to simulate various types of solid fuel combustion, including residential burning, wildfires, agricultural burning, cow dung, and plastic bag burning. The chemical composition of the particles was characterized using mass spectrometers, and new potential markers for different fuels were identified using statistical analysis. This work improves our understanding of emissions from solid fuel burning and offers support for refined source apportionment.

Carbon dioxide (CO₂) emissions from combustion sources are uncertain in many places across the globe. Satellites have the ability to detect and quantify emissions from large CO₂ point sources, including coal-fired power plants. In this study, we tasked two satellites to routinely observe CO₂ emissions at 30 coal-fired power plants between 2021 and 2022. These results present the largest dataset of space-based CO₂ emission estimates to date.

In this work, the recently developed analytical criterion for determining the boundary of nighttime ozone chemical equilibrium (NOCE) in the mesopause region (80–90 km) is used (i) to study the connection of this boundary with O and H spatiotemporal variability based on 3D modeling of chemical transport and (ii) to retrieve and analyze the spatiotemporal evolution of the NOCE boundary in 2002–2021 from the SABER/TIMED data set.

This study conducted semi-continuous measurements of PM_2.5 aerosols and their elemental composition in western Japan, during spring 2018. It analyzed the emissions, transport, and wet removal of elements such as Pb, Cu, Fe, and Mn. It also assessed the accuracy of modeled concentrations and found overestimations of BC and underestimations of Cu and anthropogenic Fe in East Asia. Insights into emissions, removals, and source apportionment of trace metals in the East Asian outflow were provided.

The study employed total ozone reactivity to demonstrate how emissions of Norway spruce readily react with ozone and could be a major ozone sink, particularly under stress. Additionally, this approach provided insight into the limitations of current analytical techniques that measure the compounds present or emitted into the atmosphere. The study shows how the technique used was not enough to measure all compounds emitted, and this could potentially underestimate various atmospheric processes.