Arctic clouds can control how much energy is absorbed by the surface or reflected back to space. Using a computer model of the atmosphere we investigated the formation of atmospheric particles that allow cloud droplets to form. We found that particles formed aloft are transported to the lowest part of the Arctic atmosphere and that this is a key source of particles. Our results have implications for the way Arctic clouds will behave in the future as climate change continues to impact the region.

This study elucidates properties and sources of volatile organic compounds (VOCs) and organic aerosol (OA) in a traffic environment. Anthropogenic VOCs (aVOCs) were clearly higher than biogenic VOCs (bVOCs), but bVOCs produced a larger portion of oxidation products. OA consisted mostly of oxygenated OA, representing secondary OA (SOA). SOA was partly associated with bVOCs, but it was also related to long-range transport. Primary OA originated mostly from traffic.

In China, the number of vehicles has jumped significantly in the last decade. This caused severe traffic congestion and aggravated air pollution. In this study, we developed a new temporal allocation approach to quantify the impacts of traffic congestion. We found that traffic congestion worsens air quality and the health burden across China, especially in the urban clusters. More effective and comprehensive vehicle emission control policies should be implemented to improve air quality in China.

Based on a field campaign in a suburban area of Shanghai during summer 2021, we calculated formaldehyde (HCHO) production rates from 24 volatile organic compounds (VOCs). In addition, HCHO photolysis, reactions with OH radicals, and dry deposition were considered for the estimation of HCHO loss rates. Our results reveal the key precursors of HCHO and suggest that HCHO wet deposition may be an important loss term on cloudy and rainy days, which needs to be further investigated.

The characteristics of n-alkanes and the contributions of various sources of PM_2.5 in the atmosphere in Beijing were studied. There were marked seasonal and diurnal differences in the n-alkane concentrations (p<0.01). Particulate-bound n-alkanes were supplied by anthropogenic and biogenic sources; fossil fuel combustion was the dominant contributor. Vehicle exhausts strongly affect PM_2.5 pollution. Controlling vehicle exhaust emissions is key to control n-alkane and PM_2.5 pollution in Beijing.

Models are essential to diagnose the significant effects of nitrogen oxides (NO_x) on air pollution. We use an air quality model to illustrate the variability of NO_x resolution-dependent simulation biases; how these biases depend on specific chemical environments, driving mechanisms, and vertical variabilities; and how these biases affect the interpretation of satellite observations. High-resolution simulations are thus critical to accurately interpret NO_x and its relevance to air quality.

To investigate the properties and origin of black carbon particles in southern Sweden during late summer, we performed measurements both at a rural site and the nearby city of Malmö. We found that local traffic emissions of black carbon led to concentrations around twice as high as those at the rural site. Modeling show that these emissions are not clearly distinguishable at the rural site, unless meteorology was favourable, which shows the importance of long-range transport and processing.

Molecular markers in organic aerosol (OA) provide specific source information on PM_2.5, and the contribution of cooking emissions to OA is significant, especially in urban environments. This study investigates the variation in concentrations and oxidative degradation of fatty acids and corresponding oxidation products in ambient air, which can be a guide for the refinement of aerosol source apportionment and provide scientific support for the development of emission source control policies.

Plume height is important in wildfire smoke dispersion and affects air quality and human health. We assess the impact of plume height on wildfire smoke dispersion and the exceedances of the National Ambient Air Quality Standards. A higher plume height predicts lower pollution near the source region, but higher pollution in downwind regions, due to the faster spread of the smoke once ejected, affects pollution exceedance forecasts and the early warning of extreme air pollution events.

Cirrus clouds affect Earth's atmosphere, deeming our study important. Here we use water vapor measurements by lidar and study the relative humidity (RHi) within and around midlatitude cirrus clouds. We find high supersaturations in the cloud-free air and within the clouds, especially near the cloud top. We study two cloud types with different formation processes. Finally, we conclude that the shape of the distribution of RHi can be used as an indicator of different cloud evolutionary stages.

We propose indices to obtain the current stage of total column ozone (TCO₃) recovery attributed to ozone-depleting substance (ODS) changes in the stratosphere. The indices are calculated using TCO₃ values in key years of the ODS changes. The ozone recovery stage is derived for 16 sites in the NH mid-latitudes using results from ground and satellite measurements and reanalysis data. In Europe, there is a slow TCO₃ recovery. A continuous TCO₃ decline has been occurring in some sites since 1980.

In 1986, soon after the discovery of the Antarctic ozone hole, NOAA began year-round ozonesonde observations at South Pole Station to measure vertical profiles of ozone and temperature from the surface to 35 km. Balloon-borne ozonesondes launched at this unique site allow for tracking all phases of the yearly springtime ozone hole beginning in late winter and after sunrise, when rapid ozone depletion begins over the South Pole throughout the month of September.

The investigation of the night-time oxidation of the most abundant hydrocarbon, isoprene, in chamber experiments shows the importance of reaction pathways leading to epoxy products, which could enhance particle formation, that have so far not been accounted for. The chemical lifetime of organic nitrates from isoprene is long enough for the majority to be further oxidized the next day by daytime oxidants.

Wind energy is one of the most essential clean and renewable forms of energy in today’s world. However, the traditional power law method generally estimates the hub-height wind speed by assuming a constant exponent between surface and hub-height wind speeds. This inevitably leads to significant uncertainties in estimating the wind speed profile. To minimize the uncertainties, we here use a machine learning algorithm known as random forest to estimate the wind speed at hub height.

Chemical compositions vary between and within particles due to the complex sources and aging processes, causing particle-to-particle heterogeneity in aerosol hygroscopicity, which is of great importance to aerosol climatic and environmental effects. This study proposes an algorithm to quantify the heterogeneity from in situ measurements, sheds light on the reanalysis of the existing H-TDMA datasets, and could have a large impact on how we use and think about these datasets.

Reactive bromine compounds, emitted by the sea ice during polar spring, play an important role in the atmospheric chemistry of the coastal regions of Antarctica. We investigate the sources and impacts of reactive bromine in detail using many years of measurements at two Antarctic sites located at opposite sides of the Antarctic continent. Using a multitude of meteorological observations, we were able to identify the main triggers and source regions for reactive bromine in Antarctica.

N-containing oxygenated organic molecules have been identified as important precursors of aerosol particles. We used an ultra-high-resolution mass spectrometer coupled with an online sample inlet to accurately measure their molecular composition, concentration level and variation patterns. We show their formation process and influencing factors in a Chinese megacity involving various volatile organic compound precursors and atmospheric oxidants, and we highlight the influence of PM_2.5 episodes.

This study develops a novel profile-based algorithm based on the ERA5 to estimate the inversion strength in the planetary boundary layer better than the previous inversion index, which is a key low-cloud-controlling factor. This improved measure is more effective at representing the meteorological influence on low-cloud variations. It can better constrain the meteorological influence on low clouds to better isolate cloud responses to aerosols or to estimate low cloud feedbacks in climate models.

Atmospheric oscillations with periods between 5 and more than 200 years are believed to be self-excited (internal) in the atmosphere, i.e. non-anthropogenic. They are found at all altitudes up to 110 km and at four very different geographical locations (75° N, 70° E; 75° N, 280° E; 50° N, 7° E; 50° S, 7° E). Therefore, they hint at a global-oscillation mode. Their amplitudes are on the order of present-day climate trends, and it is therefore difficult to disentangle them.

Convection in the Asian monsoon provides an important pathway for the transport of boundary layer and tropospheric air, and potentially pollution and chemically active species, into the stratosphere. We analyzed the distribution of the fastest and deepest convection with geostationary satellite detections for the months of May through October of 2017. We find significant differences in the geographic and monthly distributions of cross-tropopause convection across the Asian monsoon region.

The vertical motion over the Tibetan Plateau (TP) is associated with the anomalous convective activities. The diurnal variations and formation mechanisms of low clouds over the TP, Rocky Mountains and low-elevation regions are analyzed. We further discuss whether there exists a high-efficiency triggering mechanism for convection over the TP and whether there is an association among low air density and strong turbulence and ubiquitous popcorn-like cumulus clouds.

An ensemble machine-learning model coupled with chemical transport models (CTMs) was applied to assess the impact of COVID-19 on ambient benzene. The change ratio of the deweathered benzene concentration from the pre-lockdown to lockdown period was in the order of India (−23.6 %) > Europe (−21.9 %) > the United States (−16.2 %) > China (−15.6 %), which might be associated with local serious benzene pollution and substantial emission reduction in the industrial and transportation sectors.

We combine satellite measurements with a novel downscaling method to map global methane emissions at 0.1°×0.1° resolution. These fine-scale emission estimates reveal unreported emission hotspots and shed light on the roles of agriculture, wetlands, and fossil fuels for regional methane budgets. The satellite-derived emissions point in particular to missing fossil fuel emissions in the Middle East and to a large emission underestimate in South Asia that appears to be tied to monsoon rainfall.

Ozone in the lower part of the stratosphere has not increased and has perhaps even continued to decline in recent decades. This study demonstrates that the amount of ozone in this region is highly sensitive to the amount of air upwelling into the stratosphere in the tropics and that simulations from a climate model nudged to historical meteorological fields often fail to accurately capture the variations in tropical upwelling that control short-term trends in lower-stratospheric ozone.

We performed a 3-D mesoscale model study on ozone depletion events (ODEs) occurring in the spring of 2019 at Barrow using an air quality model, CMAQ. Many ODEs observed at Barrow were captured by the model, and the contribution from each physical or chemical process to ozone and bromine species during ODEs was quantitatively evaluated. We found the ODEs at Barrow to be strongly influenced by horizontal transport. In contrast, over the sea, local chemistry significantly reduced the surface ozone.

This research chemically characterises 173 different NMVOCs (non-methane volatile organic compounds) measured in real time for three seasons in the city of the central Indo-Gangetic basin of India, Lucknow. Receptor modelling is used to analyse probable sources of NMVOCs and their crucial role in forming ozone and secondary organic aerosols. It is observed that vehicular emissions and solid fuel combustion are the highest contributors to the emission of primary and secondary NMVOCs.