A high-resolution chemical transport model was used to reproduce observed smoke plumes. The model output was highly sensitive to fire emission factors and meteorology, particularly for secondary pollutant ozone. Aged urban air (age = 2 days) was the major source of ozone observed, with minor contributions from the fire. This work highlights the importance of assessing model sensitivity and the use of modelling to determine the contribution from different sources to atmospheric composition. Hide

We provide a comprehensive and critical review of laboratory studies of heterogeneous uptake of OH, NO₃, O₃, and their directly related species by mineral dust particles. The atmospheric importance of heterogeneous uptake as sinks for these species is also assessed. In addition, we have outlined major open questions and challenges in this field and discussed research strategies to address them. Hide

Particle hygroscopicity, mixing state, and the hygroscopicity of organic components were characterized in central Amazonia for 1 year; their seasonal and diel variations were driven by a combination of primary emissions, photochemical oxidation, and boundary layer development. The relationship between the hygroscopicity of organic components and their oxidation level was examined, and the results help to reconcile the differences among the relationships observed in previous studies. Hide

We investigated how the changes in atmospheric circulation of the Northern Hemisphere in winter, due to sea-ice retreat and increasing temperatures in the Arctic, may have also impacted black carbon transport and deposition to the Arctic, which may further accelerate the snow and sea-ice melting. The anthropogenic emission reductions applied in the last decades in Europe and North America were, therefore, crucial to counterbalance the most likely trend of increasing pollution in the Arctic. Hide

In this study we investigated protein nitration and decomposition by light in the presence of NO₂ via flow tube measurements. Nitrated proteins have an enhanced allergenic potential but so far nitration was only studied in dark conditions. Under irradiated conditions we found that proteins predominantly decompose while forming nitrous acid (HONO) an important precursor of the OH radical. Unlike other studies on heterogeneous NO₂ conversion we found a stable HONO formation over a long period. Hide

We present a case study of deep convection over Germany in July 2007 within the framework of the HOOVER II project. Airborne in situ measurements within the in- and outflow regions of an isolated thunderstorm provide a unique data set to study the influence of deep convection on the transport efficiency of soluble and insoluble trace gases. Despite their high solubility HCHO and H₂O₂ show enhanced concentrations in the outflow presumably due to degassing from cloud droplets during freezing. Hide

Cropland soil carbon sequestration contribute to not only climate change mitigation but also to sustainable agricultural production. This paper investigates soil carbon dynamics across the global main cereal cropping systems at a fine spatial resolution, using a modeling approach based on state-of-the-art databases of soil and climate. The key environmental controls on soil carbon changes were also identified. Hide

This work presents a method for the calibration and automated quality assurance of inversion of ceilometer profiles that is applied to the Iberian Ceilometer Network (ICENET). A cast study during an unusually intense dust outbreak affecting the Iberian Peninsula is shown. Results reveal that it is possible to obtain a quantitative optical aerosol characterization with ceilometers over large areas, and this information has a great potential for alert systems and model assimilation and evaluation. Hide

Atmospheric bacteria (bioaerosol) are transported from the Asian continental area to downwind areas in East Asia and influence climate changes, ecosystem dynamics, and human health. Aerosol samples transported for long distances were collected at high altitudes (500–3000 m) using a sophisticated helicopter-based sampling system. The high-throughput DNA sequencing remarkably revealed that the atmospheric bacterial structures at high altitudes change in response to the air mass sources. Hide

In this study, we found, due to contribution of carbonates, previously reported BC concentration in atmosphere of the Himalayas and Tibetan Plateau (HTP) were overestimated by around 39–52 %. Meanwhile, we found BC deposition of lake cores overestimated the atmospheric deposition of BC in the HTP; BC depositions of glacier region reflected actual values of 17.9 ± 5.3 mg m⁻² a⁻¹. The above results are critical for studying atmospheric distribution and chemical transport of BC in and around the HTP. Hide

Ozone is a key air pollutant. We model two geoengineering schemes, stratospheric sulfur injection and solar irradiance reduction, to compare their impacts on atmospheric ozone concentrations. With the nearly identical global mean surface temperature reduction, solar dimming increases global average surface ozone concentration, while sulfate injection decreases it. This difference is due to different stratosphere–troposphere exchange of ozone and tropospheric ozone chemistry in the two scenarios. Hide

We have observed large amounts of man-made chlorine compounds in E and SE Asia and in the upper tropical troposphere. These relatively short-lived compounds are not controlled by the Montreal Protocol, but if significant quantities were able to reach the stratosphere, the long-term recovery of stratospheric ozone would be delayed. We have also identified an important atmospheric transport mechanism that can rapidly transport these chemicals from E Asia to the upper troposphere via the tropics. Hide

São Paulo, Brazil, has relatively relaxed regulations for ambient air pollution standards and often presents high air pollution levels due to emissions of airborne particles from local sources and long-range transport of biomass burning smoke. High risks associated with particulate matter exposure were observed in most samples. The results highlighted the contribution of vehicular emissions and the significant input from biomass combustion in the dry season. Hide

We interpret a series of recent airborne and ground-based measurements with the GEOS-Chem model and its adjoint to attribute the sources of Arctic BC. Anthropogenic emissions in eastern and southern Asia make the largest contribution to Arctic BC. Gas flaring emissions from oilfields in western Siberia and from the Tarim oilfield in western China could have striking impacts on Arctic BC loadings. Hide

Oxidation flow reactors (OFRs) have been increasingly used to study atmospheric chemistry at high NO. We show that it is very difficult to obtain high-NO chemistry (in terms of RO₂ fate) in OFRs by initial NO injection. Past OFR studies with combustion sources generally had too-high precursor and NO_x concentrations that caused several types of experimental artifacts. A strong dilution (× 100 or larger) may be needed for such experiments to avoid undesired chemistry. Hide

This study investigates the importance of snowflake surface-area-to-volume ratio (SAV) for the interpretation of snowfall triple-frequency radar signatures. The results indicate that snowflake SAV has a strong impact on modeled snowfall radar signatures and therefore may be used to further constrain (the large variety and high natural variability of) snowflake shape for snowfall remote sensing, e.g., to distinguish graupel snow from snowfall characterized by large aggregate snowflakes. Hide

Using over 1000 chemical transport model simulations in the Beijing–Tianjin–Hebei region, we find that the emissions of primary inorganic PM_2.5 make the largest contribution to PM_2.5 concentrations and thus should be prioritized in PM_2.5 control strategies. Among the precursors, PM_2.5 concentrations are primarily sensitive to the emissions of NH₃, NMVOC+IVOC, and POA, and the sensitivities increase substantially for NH₃ and NH_x with the increase in emission reduction ratio. Hide

The record of the total ozone column (TOC) from stations using the Dobson ozone spectrophotometer is one of the longest geophysical records in existence. Recent adoption of a new data processing scheme, with improved results prompted a complete reprocessing of the historical record from these NOAA/NDACC sites. As the original record of TOC from these stations are used for trend analysis and satellite verification, the scientific community should be aware of the changes in the new data set. Hide

Episodes of extreme pollution events of nitrogen dioxide (NO₂) can seriously hamper air quality. But under which meteorological conditions do such extreme pollution events occur over Scandinavia? Using observational and reanalysis data it is shown that south-westerly winds (sustained for at least a few days) dominate during extreme events and cause an increase in humidity and clouds. South-easterly winds have the second largest contribution and the pollution transport is rapid when they prevail. Hide

Data records from instruments on satellites and on the ground are compared with a simulation for 1980–2016 that is made using winds and temperatures that are derived from measurements. The simulation tracks the observations faithfully after about 2000, but there are systematic errors for earlier years. Scientists must take this into account when trying to detect and quantify changes in the stratospheric circulation that are caused by climate change. Hide

Three methods are used to classify aerosol type from aerosol optical properties measured in situ at 24 surface sites. Classification methods work best at sites with stable, homogenous aerosol at particularly polluted and dust-prone continental and marine sites. Classification methods are poor at remote marine and Arctic sites. Using these methods to extrapolate aerosol type from optical properties can help determine aerosol radiative forcing and improve aerosol satellite retrieval algorithms. Hide

We derive the annual and semi-annual oscillations in cloud fraction (CF), integrated liquid water (ILW) and integrated water vapour (IWV) from the long-term measurements of the TROWARA radiometer in Bern, Switzerland. Further, we find a weekly cycle of CF and ILW from June to September with increased values on Saturday, Sunday and Monday. Hide

In this paper, influences of aerosol hygroscopic growth on the lidar ratio are studied. Results indicate that both the magnitude and vertical structures of the retrieved aerosol extinction coefficient (σ_ext) profile from lidar signals are significantly biased. This study proposes a feasible method for reducing the bias of retrieving the σ_ext profile and this method can be implemented in operational retrieval of the aerosol σ_ext profile and for pollution monitoring. Hide

Aerosols influence cloud and precipitation by modifying cloud droplet number concentrations (CDNCs). We simulate three different types of convective cloud using two different cloud microphysics parameterisations. The simulated cloud and precipitation depends much more strongly on the choice of microphysics scheme than on CDNC. The uncertainty differs between types of convection. Our results highlight a large uncertainty in cloud and precipitation responses to aerosol in current models. Hide

A few issues about surface ozone, e.g. a better understanding of spatial changes and a better assessment of ozone impacts worldwide, are still challenging. To overcome these issues, this study assessed, for the first time, the spatial and temporal changes in the projected potential ozone impacts on carbon assimilation of vegetation at global scale, by comparing the ozone potential injury at present with that expected at the end of the 21st century from different global chemistry models. Hide

The role of aerosols in the changing polar climate is not well understood and the aerosols are poorly constrained in the models. In this study we have compared output from 16 different aerosol models with available observations at both poles. We show that the model median is representative of the observations, but the model spread is large. The Arctic direct aerosol radiative effect over the industrial area is positive during spring due to black carbon and negative during summer due to sulfate. Hide

The paper presents 38 h of in situ cloud spectrometer observations of microphysical cloud properties in the Arctic, midlatitudes and tropics. The clouds are classified via particle concentrations, size distributions, and – as a novelty – small particle aspherical fractions. Cloud-type profiles are given for different temperatures and locations. The results confine regions where different cloud transformation processes occurred and emphasise the importance of small particle shape detection. Hide

Vegetation fires are a major source of NH₃ in the atmosphere. A key parameter for the calculation of their emissions, which are still uncertain, is the NH₃ enhancement ratio relative to carbon monoxide (CO), ER_NH3 / CO. Here we derive new ER_NH3 / CO ratios for large tropical regions from the measurements of IASI. We find important variability between and within the studied biomes, as well as interannual variability. This highlights the need for the development of dynamic ER_NH3 / CO ratios. Hide

Polycyclic aromatic hydrocarbons (PAHs) are hazardous pollutants with the largest emissions in East Asia. The regional WRF-Chem-PAH model has been developed to reflect the state-of-the-art understanding of current PAHs studies with several new or updated features. It is able to reasonably well simulate the concentration levels and particulate mass fractions of PAHs near the sources and at a remote outflow region of East Asia, in high spatial and temporal resolutions. Hide