Emissions of nitrogen oxides (NO_x) to the atmosphere are an ongoing air quality issue. This study directly measures emissions of NO_x and carbon dioxide from a tall tower in central London during the coronavirus pandemic. It was found that transport NO_x emissions had reduced by >73 % since 2017 as a result of air quality policy and reduced congestion during coronavirus restrictions. During this period, central London was thought to be dominated by point-source heat and power generation emissions.

Ammonia (NH₃) is an important trace gas in the atmosphere and fires are among the poorly investigated sources. During the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) aircraft campaign, we measured gaseous NH₃ and particulate ammonium (NH₄⁺) in smoke plumes emitted from 6 wildfires in the Western US and 66 small agricultural fires in the Southeastern US. We herein present a comprehensive set of emission factors of NH₃ and NH_x, where NH_x = NH₃ + NH₄⁺.

Simulations allowing ice particles to collide with one another producing more ice particles represented surface observations of ice particles accurately. An increase in ice particles formed through collisions was related to sharp changes in the wind direction and speed with height. Changes in wind speed and direction can therefore cause more enhanced collisions between ice particles and alter how fast and how much precipitation forms. Simulations were conducted with the atmospheric model COSMO.

This work finds the shifting of secondary inorganic aerosol formation mechanisms during haze aggravation and explains the decisive role of aerosol liquid water on a broader scale (~ 500 μg m³) in an ammonia-rich atmosphere based on the in situ high-resolution online monitoring datasets.

Particulate nitrate is a growing issue in air pollution. Based on comprehensive field measurement, we show heavy nitrate pollution in eastern China in summer. OH reacting with NO₂ at daytime dominates nitrate formation on clean days, while N₂O₅ hydrolysis largely enhances and become comparable with that of OH reacting with O₂ on polluted days (67.2 % and 30.2 %). Model simulation indicates that VOC : NO_x  = 2 : 1 is effective in mitigating the O₃ and nitrate pollution coordinately.

Cirrus in the tropical tropopause layer (TTL) can play a key role in vertical transport. We investigate the role of different cloud regimes and the associated ice habits in regulating the properties of the TTL. We use high-resolution numerical experiments at the scales of large-eddy simulations (LESs) and aircraft measurements. We found that LES-scale parameterizations that predict ice shape are crucial for an accurate representation of TTL cirrus and thus the associated (de)hydration process.

The impacts of atmospheric dust aerosols and cloud dynamic conditions on precipitation vertical development in southeastern China were studied using multiple satellite observations. It was found that the precipitating drops under dusty conditions grow faster in the middle layer but slower in the upper and lower layers compared with their pristine counterparts. Quantitative estimation of the sensitivity of the precipitation top temperature to the dust aerosol optical depth is also provided.

This article investigates the complex precipitation microphysics associated with super typhoon Lekima using a host of in situ and remote sensing observations, including rain gauge and disdrometer data, as well as polarimetric radar observations. The impacts of precipitation microphysics on multi-source data consistency and radar precipitation estimation are quantified. It is concluded that the dynamical precipitation microphysical processes must be considered in radar precipitation estimation.

A geostationary satellite can now provide hourly NO₂ vertical columns, and obtaining the NO₂ vertical columns from space relies on NO₂ vertical distribution from the chemical transport model (CTM). In this work, we update the CTM to better represent the chemistry environment so that the CTM can accurately provide NO₂ vertical distribution. We also find that the changes in NO₂ vertical distribution driven by a change in mixing depth play an important role in the NO₂ column's diurnal variation.

We investigated how different long-range-transported air masses can affect the microphysical properties of low-level clouds in a clean subarctic environment. A connection was revealed. Higher values of cloud droplet number concentrations were related to continental air masses, whereas the lowest values of number concentrations were related to marine air masses. These were characterized by larger cloud droplets. Clouds in all regions were sensitive to increases in cloud number concentration.

Since few studies have assessed the impacts of future combined reductions in aerosols, ozone, and their precursors on future climate change, we use models with an interactive representation of tropospheric aerosols and atmospheric chemistry schemes to quantify the impact of their reductions on the Asian climate. Our results suggest that their reductions will exacerbate the warming effect caused by greenhouse gases, increasing future climate extremes and associated population exposure risk.

Aerosol particles with sizes smaller than 50 nm impact cloud formation and precipitation. Representation of this effect is hindered by limited understanding of the properties of liquid water in these particles. Our simulations of aerosol particles containing salt or organic compounds reveal that water enters a less cohesive phase at droplet sizes below 4 nm. This effect causes important deviations from theoretical predictions of aerosol properties, including phase state and hygroscopic growth.

Global aerosol models and remote sensing retrievals use dust optical models with inconsistent and inaccurate dust shape approximations. Here, we present a new dust optical model constrained by measured dust shape distributions. This new dust optical model is an improvement on the current dust optical models used in models and retrieval algorithms, as quantified by comparisons against laboratory and field observations of dust optics.

Arctic amplification describes the recent period in which temperatures have been rising twice as fast as or more than the global average and sea ice and the Greenland ice shelf are approaching a tipping point. Hence, the Arctic ability to reflect solar energy decreases and absorption by the surface increases. Using 2 decades of complementary satellite data, we discover that clouds unexpectedly increase the pan-Arctic reflectance by increasing their liquid water content, thus cooling the Arctic.

This work comprehensively investigated the fluorescence data of light-absorbing organic compounds, water-soluble organic matter in different types of aerosol samples, soil dust, and fulvic and humic acids using an excitation–emission matrix (EEM) method and parallel factor modeling. The results revealed which light-absorbing species can be detected by EEM and also provided important information for identifying the chemical composition and possible sources of these species in atmospheric samples.

During the EMeRGe campaign in Asia, atmospheric pollutants were measured on board the HALO aircraft. The WRF-Chem model was employed to evaluate the biomass burning (BB) plume transported from Indochina and its impact on the downstream areas. The combination of BB aerosol enhancement with cloud water resulted in a reduction in incoming shortwave radiation at the surface in southern China and the East China Sea, which potentially has significant regional climate implications.

Previous box model studies applied different timescales of observational datasets to identify the O₃–precursor relationship, but there is a lack of comparison among these different timescales regarding the impact of O₃ formation chemistry. Through a case study at Zibo in China, we find that the O₃ formation regime showed overall consistency but non-negligible variability among various patterns of timescale. This would be complementary in developing more accurate O₃ pollution control strategies.

We evaluate the spatiotemporal variability of peroxy acyl nitrates (PANs), important photochemical pollutants, over Mexico City using satellite observations. PANs exhibit a seasonal cycle that maximizes in spring. Wildfires contribute to observed interannual variability, and the satellite indicates several areas of frequent outflow. Recent changes in NO_x emissions are not accompanied by changes in PANs. This work demonstrates analysis approaches that can be applied to other megacities.

Wetlands cover a substantial fraction of the land mass in the northern latitudes, from northern Europe to Siberia and Canada. Yet, their isoprene and terpene emissions remain understudied. Here, we used a state-of-the-art measurement technique to quantify ecosystem-scale emissions from a boreal wetland during an unusually warm spring/summer. We found that the emissions from this wetland were (a) higher and (b) even more strongly dependent on temperature than commonly thought.

We evaluated six atmospheric transport models for their capability to simulate the CO₂ plumes from two of the largest power plants in Europe by comparing the models against aircraft observations collected during the CoMet (Carbon Dioxide and Methane Mission) campaign in 2018. The study analyzed how realistically such plumes can be simulated at different model resolutions and how well the planned European satellite mission CO2M will be able to quantify emissions from power plants.

We find that cloud profiles can be divided into four prominent patterns, and the frequency of these four patterns is related to intensities of cloud-top entrainment and precipitation. Based on these analyses, we further propose a cloud profile parameterization scheme allowing us to represent these patterns. Our results shed light on how to facilitate the representation of cloud profiles and how to link them to cloud entrainment or precipitating status in future remote-sensing applications.

In summer 2019 at Mt. Bachelor Observatory, we observed smoke from wildfires with transport times ranging from less than a day up to 2 weeks. Aerosol absorption of multi-day transported smoke was dominated by black carbon, while smoke with shorter transport times had greater brown carbon absorption. Notably, Siberian smoke exhibited aerosol scattering and physical properties indicative of contributions from larger particles than typically observed in smoke.

Amines are compounds emitted from a variety of marine and continental sources and were measured by aerosol mass spectrometry and Fourier transform infrared spectroscopy during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) cruises. Secondary continental and primary marine sources of amines were identified by comparisons to tracers. The results show that the two methods are complementary for investigating amines in the marine environment.

An increase in aerosol concentration (tiny airborne particles) is shown to suppress rainfall and increase the abundance of droplets in clouds passing over Graciosa Island in the Azores. Cloud drops remain affected by aerosol for several days across thousands of kilometers in satellite data. Simulations from an Earth system model show good agreement, but differences in the amount of cloud water and its extent remain despite modifications to model parameters that control the warm-rain process.

Using different transport models results in large errors in optimized fluxes in the atmospheric inversions. Boundary conditions and inversion system configurations lead to a smaller but non-negligible impact. The findings highlight the importance to validate transport models for further developments but also to properly account for such errors in inverse modelling. This will help narrow the convergence of gas estimates reported in the scientific literature from different inversion frameworks.

This study investigates the influence of the winter large-scale circulation on daily concentrations of PM_2.5 and their sensitivity to emissions. The new proposed circulation index can effectively distinguish different levels of air pollution and explain changes in PM_2.5 sensitivity to emissions from local and surrounding regions. We then project future changes in PM_2.5 concentrations using this index and find an increase in PM_2.5 concentrations over the region due to climate change.

The effects of aerosols on lightning are complex and still far from understood. We analysed the impacts of aerosols on lightning activity in the Sichuan Basin. Results show that lightning flashes first increase with aerosol loading during all periods and then behave differently (decrease in the afternoon and flatten at night). This suggests that the changes in solar radiation can modulate the aerosol effects on the occurrence and development of convection and lightning activity.

We compared non-phenolic and phenolic methoxybenzaldehydes as photosensitizers for aqueous secondary organic aerosol (aqSOA) formation under cloud and fog conditions. We showed that the structural features of photosensitizers affect aqSOA formation. We also elucidated potential interactions between photosensitization and ammonium nitrate photolysis. Our findings are useful for evaluating the importance of photosensitized reactions on aqSOA formation, which could improve aqSOA predictive models.

Limited knowledge is available on volatile organic compound (VOC) multi-site research of different land-use types at city level. This study performed a concurrent multi-site observation campaign on the three typical land-use types of Shanghai, East China. The results showed that concentrations, sources and ozone and secondary organic aerosol formation potentials of VOCs varied with the land-use types.

This study shows that smoke layers can reach the tropopause via the self-lofting effect within 3–7 d in the absence of pyrocumulonimbus convection if the aerosol optical thickness is larger than approximately 2 for a longer time period. When reaching the stratosphere, wildfire smoke can sensitively influence the stratospheric composition on a hemispheric scale and thus can affect the Earth’s climate and the ozone layer.