We investigated the ice-nucleating abilities of particulate emissions from a modern diesel engine using the portable ice-nuclei counter SPIN, a continuous-flow diffusion chamber instrument. Three different fuels were studied without blending, including fossil diesel and two renewable fuels, testing different emission aftertreatment systems and photochemical aging. We found that the diesel emissions were inefficient ice nuclei, and aging had no or little effect on their ice-nucleating abilities.

The aerosol distribution over Haifa, Israel, was measured for 2 years by a laser-based vertically resolved measurement technique called lidar. From these data, the aerosol types and their percentages of the observed aerosol mixtures were identified in terms of their size and shape. We found mostly desert dust from the surrounding deserts and sea salt from the close-by Mediterranean Sea. But aerosols from anthropogenic and industrial pollution from local and far away sources were also detected.

High concentrations of ice particles were observed at temperatures greater than about –8 C. The default scheme of the secondary ice production cannot explain the high concentrations. Relaxing the conditions for secondary ice production or considering dust aerosol alone is insufficient to produce the observed amount of ice particles. It is likely that multi-thermals play an important role in producing very high concentrations of secondary ice particles in some tropical clouds.

This study shows that in most years when haze pollution (HP) over the North China Plain (NCP) is more (less) serious in winter, air conditions in the following spring are also worse (better) than normal. Conversely, there are some years when HP in the following spring is opposed to that in winter. It is found that North Atlantic sea surface temperature (SST) anomalies play important roles in HP evolution over the NCP. Thus North Atlantic SST is an important preceding signal for NCP HP evolution.

Our simulations indicate that the recently identified production and subsequent condensation effect of extremely low-volatility organic compounds have a smaller-than-expected effect on the total concentration of atmospheric particles. On the other hand, the oxidation of intermediate-volatility organic compounds leads to decreases in the ultrafine-particle concentrations. These results improve our understanding of the links between secondary organic aerosol formation and ultrafine particles.

The Fires, Asian, and Stratospheric Transport–Las Vegas Ozone Study (FAST-LVOS) combined lidar, aircraft, and in situ measurements with global models to investigate the contributions of stratospheric intrusions, regional and Asian pollution, and wildfires to background ozone in the southwestern US during May and June 2017 and demonstrated that these processes contributed to background ozone levels that exceeded 70 % of the US National Ambient Air Quality Standard during the 6-week campaign.

Aerosols are simulated in a simplified way in climate models: in the model analyzed here, they are represented in every grid as described by three simple logarithmic distributions, mixing all different species together. The size can evolve when new particles are formed, particles merge together to create a larger one or particles are deposited to the surface. This approximation normally works fairly well. Here we show however that when large amounts of sulfate are simulated, there are problems.

We argue that the illustration employed by Huang et al. (2015) to demonstrate the transport of Asian dust to the high Arctic was, in fact, largely a cloud event and that the actual impact of Asian dust was measurable but much weaker than what they proposed and had occurred a day earlier (in agreement with the transport model they had employed to predict the transport path to the high Arctic).

Wildfires are increasing in extent and severity, driven by climate change. Such fires emit large amounts of volatile organic compounds (VOCs) to the atmosphere. Many of these, such as the furans studied here, are very reactive and are rapidly converted to other VOCs, which are expected to have negative health effects and to further impact the climate. Here, we establish the importance of the nitrate radical for removing these compounds both during the night and during the day.

We present a new implementation of an ensemble-based data assimilation method to improve forecasting of volcanic aerosols. This system can be efficiently integrated into operational workflows by exploiting high-performance computing resources. We found a dramatic improvement of forecast quality when satellite retrievals are continuously assimilated. Management of volcanic risk and reduction of aviation impacts can strongly benefit from this research.

Using a novel setup, we comprehensively characterized the formation of particle-bound reactive oxygen species (ROS) in anthropogenic and biogenic secondary organic aerosols (SOAs). We found that more than 90 % of all ROS components in both SOA types have a short lifetime. Our results also show that photochemical aging promotes particle-bound ROS production and enhances the oxidative potential of the aerosols. We found consistent results between chemical-based and biological-based ROS analyses.

Every spring in the Arctic, a series of photochemical events occur over the ice-covered ocean, known as bromine explosion events, ozone depletion events, and mercury depletion events. Here we report the re-creation of these events at an outdoor sea ice facility in Winnipeg, Canada, far away from the Arctic. The success provides a new platform with new opportunities to uncover fundamental mechanisms of these Arctic springtime phenomena and how they may change in a changing climate.

The black carbon (BC) vertical profile plays a critical role in BC–meteorology interaction, which also influences PM_2.5 concentrations. More BC mass was assigned into high altitudes (above 1000 m) in the model, which resulted in a stronger cooling effect near the surface, a larger temperature inversion below 421 m, more reductions in PBLH, and a larger increase in near-surface PM_2.5 in the daytime caused by the direct radiative effect of BC.

Via combining laboratory and modeling work, we found that heterogeneous reaction of N₂O₅ with saline mineral dust aerosol could be an important source of tropospheric ClNO₂ in inland regions.

We developed an input-adaptive mixed-effects model, which was automatised to select the best combination of input variables, including up to three fixed effect variables and three time indictors as random effect variables. We tested the model to estimate lung-deposited surface area (LDSA), which correlates well with human health. The results show the inclusion of time indicators improved the sensitivity and the accuracy of the model so that it could serve as a network of virtual sensors.

Ammonia is one of the main components of nitrogen deposition. Here we use a new model to assess the ammonia emissions from agriculture, the largest anthropogenic source of ammonia. The model results are consistent with earlier estimates over industrialized regions in agreement with observations. However, the model predicts much higher emissions over sub-Saharan Africa compared to earlier estimates. Available observations from surface stations and satellites support these higher emissions.

Surface ozone and temperature are strongly dependent and their extremes might be exacerbated by underlying climatological drivers, such as atmospheric blocking. Using an observational data set, we measure the dependence structure between ozone and temperature under the influence of atmospheric blocking. Blocks enhanced the probability of occurrence of compound ozone and temperature extremes over northwestern and central Europe, leading to greater health risks.

This paper completes the companion paper of Córdoba-Jabonero et al. (2021). We estimate the total direct radiative effect produced by mineral dust particles during the June 2019 mega-heatwave at two sites in Spain and Germany. The results show that the dust particles in the atmosphere contribute to cooling the surface (less radiation reaches the surface) and that the heatwave (parametrized by high surface and air temperatures) contributes to reducing this cooling.

Our work pioneered land-use machine learning methods for developing link-level emission inventories, utilizing hourly traffic profiles, including volume, speed, and fleet mix, obtained from the governmental intercity highway monitoring network in the "capital circles" of China. This research provides a platform to realize the near-real-time process of establishing high-resolution vehicle emission inventories for policy makers to engage in sophisticated traffic management.

This study explores the effect of pyruvic acid (PA) both in the SO₃ hydrolysis and in sulfuric-acid-based aerosol formation. Results show that in dry and polluted areas, PA-catalyzed SO₃ hydrolysis is about 2 orders of magnitude more efficient at forming sulfuric acid than the water-catalyzed reaction. Moreover, PA can effectively enhance the ternary SA-PA-NH₃ particle formation rate by up to 4.7×10² relative to the binary SA-NH₃ particle formation rate at cold temperatures.

The modelling study focuses on the importance of ice multiplication processes in orographic mixed-phase clouds, which is one of the least understood cloud types in the climate system. We show that the consideration of ice seeding and secondary ice production through ice–ice collisional breakup is essential for correct predictions of precipitation in mountainous terrain, with important implications for radiation processes.

Chemical reactions with iron in clouds and aerosol form and cycle reactive oxygen species (ROS). Previous model studies assumed that all cloud droplets (particles) contain iron, while single-particle analyses showed otherwise. By means of a model, we explore the bias in predicted ROS budgets by distributing a given iron mass to either all or only a few droplets (particles). Implications for oxidation potential, radical loss and iron oxidation state are discussed.

The contribution of various pollution sources to the variability of fine PM in an urban area was examined using as an example the city of Pittsburgh. Biomass burning aerosol shows the largest variability during the winter with local maxima within the city and in the suburbs. During both periods the largest contributing source to the average PM_2.5 is particles from outside the modeling domain. The average population-weighted PM_2.5 concentration does not change significantly with resolution.

This study characterizes size-resolved particle effective densities and their evolution associated with emissions and aging processes in a rural area of the North China Plain. Particle effective density exhibits a high-frequency bimodal distribution, and two density modes exhibit opposite trends with increasing particle size. SIA and BC mass fractions are key factors of particle effective density, and a value of 0.6 g cm⁻³ is appropriate to represent BC effective density in bulk particles.

We show airborne in situ measurements of the very short-lived ozone-depleting substances CH₂Cl₂ and CHCl₃, revealing particularly high concentrations of both species in the lower stratosphere. Back-trajectory calculations and 3D model simulations show that the air masses with high concentrations originated in the Asian boundary layer and were transported via the Asian summer monsoon. We also identify a fast transport pathway into the stratosphere via the North American monsoon and by hurricanes.

The stratosphere is an important source of tropospheric ozone, which affects climate, chemistry, and air quality, but is extremely difficult to quantify given the large production and loss terms in the troposphere. Here, we use other gases that are well observed and quantified as a reference to test our simulations of ozone transport in the atmosphere. This allows us to better constrain the stratospheric source of ozone and also offers guidance to improve future simulations of ozone transport.

The CMIP6 models' simulated dust processes are getting more uncertain as models become more sophisticated. Of particular challenge are the links between dust cycles and optical properties, and we recommend more detailed output relating to dust cycles in future intercomparison projects to constrain such links. Also, models struggle to capture certain key regional dust processes such as dust accumulation along the slope of the Himalayas and dust seasonal cycles in North China and North America.

Evaluating methane (CH₄) sources in the Athabasca oil sands region (AOSR) is crucial to effectively mitigate CH₄ emissions. We tested the use of carbon isotopes to estimate source contributions from key CH₄ sources in the AOSR and found that 56 ± 18 % of CH₄ emissions originated from surface mining and processing facilities, 34 ± 18 % from tailings ponds, and 10 ± < 1 % from wetlands, confirming previous findings and showing that this method can be successfully used to partition CH₄ sources.

Marine low-level clouds cover vast areas of the Southern Ocean, and they are essential to the Earth system energy balance. We use 3 years of satellite observations to group low-level clouds by their spatial structure using a pattern-recognizing program. We studied two primary cloud type patterns, i.e. open and closed clouds. Open clouds are uniformly distributed over the storm track, while closed clouds are most predominant in the southeastern Indian Ocean. Closed clouds exhibit a daily cycle.

The relative impact of cloud condensation nuclei (CCN) concentrations and the shape parameter of the cloud droplet size distribution is evaluated in realistic convection-resolving simulations. We find that an increase in the shape parameter can produce almost as large a variation in precipitation as a CCN increase from maritime to polluted conditions. The choice of the shape parameter may be more important than previously thought for determining cloud radiative characteristics.

Based on the OBM-MCM model analyses, the study aims to clarify (1) the pollution characteristics of O3 and its precursors, (2) the atmospheric oxidation capacity and radical chemistry, and (3) the O₃ formation mechanism and sensitivity analysis. The results are expected to enhance the understanding of the O₃ formation mechanism with low O₃ precursor levels and provide scientific evidence for O₃ pollution control in coastal cities.