Exceedances of legal thresholds for urban air pollution are of wide concern. We demonstrate the usefulness of very high-resolution modelling for the assessment of air pollution in the urban space on the example of Bergen, Norway. Vulnerability maps highlight areas with high pollutant loading and pathways for pollutant dispersion. This supports the understanding of urban air pollution beyond existing, scarce monitoring networks and possibly the mitigation of impacts on the local population.

Highly oxygenated organic molecules have been suggested to form a large part of secondary organic aerosol. However, with their exotic structures, their volatilities are not well known, making their exact role in particle formation hard to assess. In laboratory experiments, we found the volatility of HOMs formed in the ozonolysis of the monoterpene alpha-pinene to be in the middle of earlier estimates. The volatilities of HOMs could be well explained in terms of their molecular formulae.

This study combines surface-level air quality measurements with satellite imagery and back-trajectory modeling to investigate the long-distance transport of these emissions to the New York City metropolitan area and the northeastern US. Two events in August 2018 were traced to biomass burning on the western coast of Canada and from the southeastern US, highlighting the importance of understanding long-distance transport of fire emissions in air quality planning.

Observations of low–temperature cirrus clouds have found unexpectedly low ice crystal numbers and high supersaturations, suggesting an incomplete understanding of the freezing mechanisms under these conditions. The existence of viscous organic aerosol has offered alternative ice nucleation pathways, which have been observed in laboratory studies. We have developed the first cloud parcel model to investigate the effect of viscosity on ice nucleation.

Saturated alcohols (SAs), such as (E)-4-methylcyclohexanol, 3,3-dimethyl-1-butanol, and 3,3-dimethyl-2-butanol, could be used as biofuels. The atmospheric reactivity of these compounds must be established in order to understand the consequences of the presence of these compounds in the atmosphere. The experimental results obtained in this work reveal that uncontrolled emissions of these saturated alcohols could have important atmospheric implications.

An innovative approach is developed to preprocess monitored wet deposition data of inorganic ions for generating their decadal trends. Differing from traditional approaches which directly apply annual or seasonal average data to trend analysis tools, the proposed new approach makes use of slopes of regression equations between a series of study years and a climatology (base) year in terms of monthly averaged data. The new approach yields more robust results than the traditional tools.

Delhi, India, is the most polluted megacity on the planet, posing acute challenges to public health. We report on source apportionment conducted on 15 months of highly time-resolved mass spectrometer data. We find that severe air pollution episodes are dominated by primary organic aerosol, while secondary organic aerosol dominates the fractional contributions year-round, suggesting the importance of sources as well as their atmospheric processing on pollution levels in Delhi.

The tropical tropopause layer is an important atmospheric region right in between the troposphere and the stratosphere. We evaluate the representation of this layer in reanalyses data sets, which create a complete picture of the state of Earth's atmosphere using atmospheric modeling and available observations. The recent reanalyses show realistic temperatures in the tropical tropopause layer. However, where the temperature is lowest, the so-called cold point, the reanalyses are too cold.

Particulate nitrate is one of the most important climate cooling agents. Our results show that interaction with sea-salt aerosol can shift nitrate to larger sized particles (redistribution effect), weakening its direct cooling effect. The modelling results indicate strong redistribution over coastal and offshore regions worldwide as well as continental Europe. Improving the consideration of the redistribution effect in global models fosters a better understanding of climate change.

This study compares in situ measurements of temperature and humidity in the upper troposphere and lower stratosphere with reanalysis data from the ECMWF ERA-Interim data set. It is shown that temperature compares well between both data sets. However, extreme values of relative humidity with respect to ice (RH_i) are missing in ERA-Interim, and hence the number and size of ice supersaturated regions differ strongly between both data sets.

In this work, methane representation in AM4.1 is improved by optimizing CH₄ emissions to match surface observations. We find increases in CH₄ sources balanced by increases in sinks lead to CH₄ stabilization during 1999–2006, and anthropogenic sources (e.g., agriculture, energy, and waste) are more likely major contributors to the renewed growth after 2006. Increases in CH₄ emissions and decreases in OH levels during 2008–2015 prolong CH₄ lifetime and amplify methane response to emission changes.

Although atmospheric dust particles produce significant impacts on the Earth system, most climate models still have difficulty representing the basic processes that affect these particles. In this study, we present new constraints on dust properties that consistently outperform the conventional climate models, when compared to independent measurements. As a result, our constraints can be used to improve climate models or serve as an alternative in constraining dust impacts on the Earth system.

A new method was developed to calculate hygroscopicity parameter κ of organic aerosols (κ_OA) based on aerosol light-scattering measurements and bulk aerosol chemical-composition measurements. Derived high-time-resolution κ_OA varied in a wide range (near 0 to 0.25), and the organic aerosol oxidation degree significantly impacts variations in κ_OA. Distinct diurnal variation in κ_OA is found, and its relationship with oxygenated organic aerosol is discussed.

The Tibetan Plateau (TP) plays a vital role in regional and global climate change due to its location and orography. After generating a long-term surface radiation (SR) dataset, we characterized the SR spatiotemporal variation along with temperature. Evidence from multiple data sources indicated that the TP dimming was primarily driven by increased aerosols from human activities, and the cooling effect of aerosol loading offsets TP surface warming, revealing the human impact on regional warming.

In this study the aerosol liquid water content (ALWC) is determined from aerosol hygroscopic growth factor (GF) measurement (ALWC_HTDMA) and also simulated by the ISORROPIA II thermodynamic model (ALWC_ISO). We found that ALWC contributed by organics (ALWC_Org) accounts for 30 % ± 22 % of the total ALWC in winter in Beijing. A case study reveals that ALWC_Org plays an important role in the formation of secondary aerosols through multiphase reactions at the initial stage of a heavy-haze episode.

Aerosol effects on visibility and climate are influenced by their hygroscopicity. By contrasting data from two techniques between summer and winter in Beijing, we investigate the effect of aerosol aging, mixing state, and local sources on its hygroscopicity. We revealed that inappropriate use of the density of BC and organics results in large uncertainty in calculating aerosols hygroscopicity. Our results are helpful for parameterization in models.

We introduce a multi-model, multi-constituent chemical data assimilation framework that directly accounts for model error in transport and chemistry by integrating a portfolio of forward chemical transport models. The assimilation was able to reduce ensemble forward model spread and bias relative to independent measurements. Diagnostic information readily available from the framework has the potential to improve chemical predictions through relationships such as emergent constraints.

The differences between these six BB emission datasets are large. Our study found that (1) most current biomass burning (BB) aerosol emission datasets derived from satellite observations lead to the underestimation of aerosol optical depth (AOD) in this model in the biomass-burning-dominated regions and (2) it is important to accurately estimate both the magnitudes and spatial patterns of regional BB emissions in order for a model using these emissions to reproduce observed AOD levels.

Fire is a natural phenomenon that has a long history of interactions with the environment and human activity. The complex interactions were less represented in previous fire and climate models. Here we use a new global fire model with improved modeling capability to study how fire responds and contributes to climate change. The modeling results show increased global fire activity in the future driven by climate change, which in turn modulates local and remote climate and ecosystems.

Oxidation chemistry of organic compounds in the atmosphere produces a diverse spectrum of products. This diversity is difficult to represent in air quality and climate models, and in laboratory experiments it results in large and complex datasets. This work evaluates several methods to simplify the chemistry of oxidation systems in environmental chambers, including positive matrix factorization, hierarchical clustering analysis, and gamma kinetics parameterization.

This paper presents temporal evolution of stratospheric chlorine and minor species related to Antarctic ozone depletion, based on FTIR measurements at Syowa Station, and satellite measurements by MLS and MIPAS in 2007 and 2011. After chlorine reservoir species were processed on PSCs and active ClO was formed, different chlorine deactivation pathways into reservoir species were identified, depending on the relative location of Syowa Station to the polar vortex boundary.

We address, on the molecular level, the potential for, and consequences of, surface property variations in aerosol particles in the atmosphere. Aerosol surface aging changes the interfacial chemistry, giving rise to marked variations in the ice nucleation ability of the surface. This study provides new insights into atmospheric processes, particularly cloud formation and aerosol aging in the atmosphere, with potential implications for the pharmaceutical and food industries.

Previous measurements of water vapor in the upper troposphere and lower stratosphere (UT/LS) have shown unexpectedly high concentrations of water vapor in ice clouds, which may be due to an incomplete understanding of the structure of ice and the behavior of ice growth in this part of the atmosphere. Water vapor measurements during the 2013 IsoCloud campaign at the AIDA cloud chamber show no evidence of this anomalous supersaturation in conditions similar to the real atmosphere.

We have explored the nature and stability of molecules that give biomass burning smoke its faint brown color. Different types of biomass fuels were burned and the resulting smoke was collected for a detailed chemical analysis. We found that brown molecules in smoke become less colored when they are irradiated by sunlight, but this photobleaching process is very slow. This means that biomass burning smoke will remain brown-colored for a long time and efficiently warm up the atmosphere.

The vertical evolution of the cloud effective radius reflects the precipitation-forming process. We developed an algorithm for retrieving it based on objective cloud-cluster identification rather than the subjective polygon of the conventional method. The profile shows completely different morphologies in different life stages of the cloud cluster, which is important in the characterization of the formation of precipitation and the temporal evolution of microphysical processes.

Topic 3 of the Model Inter-Comparison Study for Asia (MICS-Asia) Phase III examines how online coupled air quality models perform in simulating high aerosol pollution in the North China Plain region during wintertime haze events and evaluates the importance of aerosol radiative feedbacks. This paper discusses the estimates of aerosol radiative forcing, aerosol feedbacks, and possible causes for the differences among the models.

The effectiveness of transport of short-lived halocarbons to the upper troposphere and lower stratosphere remains an important unknown in quantifying the supply of ozone-depleting substances to the stratosphere. In early 2014, a major field campaign in Guam in the western Pacific, involving UK and US research aircraft, sampled the tropical troposphere and lower stratosphere. The resulting measurements of CH₃I, CHBr₃ and CH₂Br₂ are compared here with calculations from a Lagrangian model.

Gas-phase autoxidation of organics can generate highly oxygenated organic molecules (HOMs) and thus increase secondary organic aerosol production and enable new-particle formation. Here we explicitly represent the generation of HOMs via peroxy radical chemistry and resolve the products based on volatility and O : C. Using experimentally constrained assumptions about autoxidation and dimerization reactions, we see suppression of HOM formation under low-temperature and high-NO_x conditions.

In this study, we focus on explaining the concentration variations in the observed particle modes, by relating them to the potential aerosol sources and sinks, and on understanding the connections between these modes. Interestingly, even in the atmospheric cocktail in urban Beijing, secondary new particle formation (NPF) drives the particle number concentration, especially in the sub-3 nm range. We found that the total number concentration is ~ 4 times higher on NPF days than on haze days.