During riming of graupel and hail, soluble chemical trace constituents contained in the liquid droplets could be retained while freezing onto the glaciated particle, or released back to the air potentially at other altitudes as retained. Quantification of retention constitutes a major uncertainty in numerical models for atmospheric chemistry and improvements hinge upon experimental determination of retention for carboxylic acids, aldehydes, SO₂, H₂O₂, NH₂, and others, as presented in this paper.

Little is known of the integrated impacts of HONO and ClNO₂ on lower-tropospheric ozone so far. In this study, we updated WRF-Chem with the CBMZ_ReNOM module, which considers both the sources and chemistry of HONO and ClNO₂. The revised model revealed that the two reactive nitrogen compounds significantly affected the oxidation capacity and ozone formation at the surface and within the lower troposphere over polluted regions and noticeably improved summertime O₃ predictions over China.

Recently, theoretical and laboratory studies have suggested an additional nighttime channel of transfer of vibrational energy of OH molecules to CO₂ in the mesosphere and lower thermosphere (MLT). We show that new mechanism brings modelled 4.3 μm emissions very close to the SABER/TIMED measurements. This renders new opportunities for the application of the CO₂ 4.3 μm observations in the study of the energetics and dynamics of the nighttime MLT.

We estimate representativeness errors in observations due to mismatching spatio-temporal sampling, on timescales of hours to a year and length scales of 50 to 200 km, for a variety of observing systems (in situ or remote sensing ground sites, satellites with imagers or lidar, etc.) and develop strategies to reduce them. This study is relevant to the use of observations in constructing satellite L3 products, observational intercomparison and model evaluation.

Human activities have substantially enhanced atmospheric deposition of reactive nitrogen, inducing complex environmental consequences. This study presents a first quantitative investigation of how anthropogenic nitrogen deposition could impact surface ozone air quality through surface–atmosphere exchange processes. We find important surface ozone changes driven by nitrogen deposition, which can be comparable with those due to historical climate and land use changes.

Unmanned aerial vehicles are equipped with meteorological sensors to measure cloud properties. The measurements are used to calculate the amount of solar radiation reflected by the clouds and compared to simulation results. The uncertainties related to radiative forcing in the simulations are from the lack of mixing in the boundary layer and mixing of dry air into the cloud top. Conservative variables are used to calculate the amount of air mixed into cloud top to minimize these uncertainties.

Cloud droplet number concentration is linked to air pollution levels via indirect aerosol effects. The climatological results presented here provide constraints on cloud droplet number concentration globally, thereby helping to evaluate global climate models and study the impact of pollution regionally and globally.

The optical properties of aerosols are required to analyse measurements of aerosol properties, estimate radiative forcing and interpret remote sensing retrievals. We provide comprehensive data sets of the refractive indices of the most important inorganic aerosol constituents, reporting parameterisations for the wavelength and relative humidity dependencies for each system. We assess the accuracy of this study, made on single trapped particles, against previous less comprehensive data sets.

Limonene is emitted in substantial quantities by plants, and also has indoor sources from air fresheners and cleaning products. We studied particle formation from the oxidation of limonene and found substantial quantities of oxidising components which are thought to be associated with the negative health effects of particulates. State-of-the-art measurements of the products of limonene–ozone chemistry were also presented.

The assessment of the impacts of aerosol direct effects (ADE) is important for understanding emission reduction strategies that seek co-benefits associated with reductions in both particulate matter and ozone. This study quantifies the ADE impacts on tropospheric ozone by using a two-way coupled meteorology and atmospheric chemistry model. Results suggest that reducing ADE may have the potential risk of increasing ozone in winter, but it will benefit the reduction of maxima ozone in summer.

Cloud events at Mt. Tai were investigated for the chemical composition and size distribution of cloud droplets. An obvious rise in pH was found for elevated NH⁺₄ during the last decade. Higher PM_2.5 levels resulted in higher concentrations of water-soluble ions, smaller sizes and higher numbers of cloud droplets. The mechanism of cloud-droplet formation and the mass transfer between aerosol–gas–cloud phases were summarized to enrich the knowledge of cloud chemical and microphysical properties.

Inorganic bromine (Br_y) plays an important role in ozone layer depletion. Based on aircraft observations of organic bromine species and chemistry simulations, we model the Br_y abundances over the Pacific tropical tropopause. Our results show BrO and Br as the dominant species during daytime hours, and BrCl and BrONO₂ as the nighttime dominant species over the western and eastern Pacific, respectively. The difference in the partitioning is due to changes in the abundance of O₃, NO₂, and Cl_y.

The CAMx regional model was used to examine contribution of intercontinental transport over North America as part of AQMEII Phase III. Largest boundary condition (BC) contributions to ozone (O₃) are from the mid-troposphere. Lower emissions in Asia by 20 % causes a near-linear relationship between the BC O₃ changes and surface O₃ changes in the western US, but the changes are less than 1 ppb. Using inert tracers leads to high bias over 10 ppb compared to using chemically reactive tracers.

This paper presents the results from a 5-year and near-real-time measurement study of carbonaceous aerosols in PM_2.5 conducted at an urban site in Shanghai. Moreover, we integrated the results from historical field measurements and satellite observations, concluding that carbonaceous aerosol pollution in Shanghai has gradually reduced since 2006. This can be largely explained by the introduction of air-cleaning measures such as controlling vehicular emissions.

The oxidative potential of secondary organic aerosol (SOA) was measured by dithiothreitol assay. To quantify the reactive functional groups of particulate oxidizers that can increase dithiothreitol response, the quantities of quinones, organic hydroperoxides, and peroxy acyl nitrates were measured by chemical assays. Organic hydroperoxides were largely attributed to the oxidative potential of SOA. The results provide a deep understanding of the mechanistic role of SOA in modifying biomolecules.

Seasonal changes in chemical compositions, sources, and evolution for submicron aerosols in the megacity Beijing were investigated based on high-resolution AMS measurements. Carbonaceous fraction (OA+BC) constituted over 50 % of PM₁ in autumn due to primary emissions, while SNA contributed 60 % to PM1 in other seasons. Secondary components (OOA+SNA) contributed ~ 60–80 % to PM1, suggesting that secondary formation played an important role in PM pollution. OA was in a relatively high oxidation state.

Mineral dust is an important sink for sulfur dioxide that can be oxidized and further influence the acidification of particles as well as cloud formation. In this study, a model was developed to capture the importance of mineral dust on sulfate formation in various environments. The results suggest that the oxidation of sulfur dioxide is greatly promoted in the presence of dust particles. Our model is helpful to enhance the accuracy of sulfate formation predicted.

Experiments on organic aerosol formation are important for our understanding of climate. Recent experiments on the reaction of ozone with alpha-pinene showed high production of extremely low-volatility organics. This appeared to contradict prior volatility distributions derived from equilibrium partitioning. We examined this using a dynamic volatility basis set model and found that the delay between the production and condensation of organics is integral to reconciling this difference.

We study the effects of aerosol particles and updraft speed on the warm phase of Amazonian clouds. We expand the sensitivity analysis usually found in the literature by concomitantly considering cloud evolution and the effects on droplet size distribution (DSD) shape. The quantitative results show that particle concentration is the primary driver for the vertical profiles of effective diameter and droplet concentration in the warm phase of Amazonian convective clouds.

We present the PathfinderTURB algorithm for the analysis of ceilometer backscatter data and the real-time detection of the vertical structure of the planetary boundary layer. PathfinderTURB has been applied to 1 year of data measured by two ceilometers operated at two Swiss stations: the Aerological Observatory of Payerne on the Swiss plateau, and the Alpine Jungfraujoch observatory. The study shows that aerosols from the boundary layer significantly influence the air measured at Jungfraujoch.

We use observations of nitrogen dioxide columns from multiple satellite instruments with the help of a chemical transport model to constrain the global deposition of reactive nitrogen oxides (NO_y) over the last 2 decades. NO_y deposition decreased by up to 60 % in eastern North America, doubled in regions of East Asia, and declined by 20 % in parts of Western Europe. We also find changes in the export of NO_y via atmospheric transport, with direct impacts on countries downwind of source regions.

We quantify the main sources that have contributed to fine particulate matter (PM_2.5) between 1998 and 2012 in Santiago's downtown. We calculate the long-term trend as well as abrupt changes in the time series and show how these relate to particular government policies implemented to improve air quality in specific years. We thus identify which measures successfully reduced individual sources and which sources need measures to avoid episodes when PM_2.5 concentrations surpass Chilean standards.

Based on the future projection of high-resolution regional climate simulations under the medium-low radiative forcing scenario, the haze pollution potential tends to increase almost over the whole of China except central China, and this increase would be generally aggravated over time. There would be a higher probability of pollution risk over Beijing–Tianjin–Hebei and Yangtze River Delta in winter, over Pearl River Delta in spring and summer, and over Northeast China throughout the whole year.

To evaluate the quality of the satellite-derived NO_x emissions, we compare nine emission inventories of nitrogen oxides including four satellite-derived NO_x inventories and bottom-up inventories for East Asia. The temporal and spatial distribution of NO_x emissions over East Asia are evaluated. We analyse the differences in satellite-derived emissions from two different inversion methods. The paper ends with recommendations for future improvements of emission estimates.

Atmospheric emissions of CCl₄ are regulated by the Montreal Protocol due to its role as a strong ozone-depleting substance. The molecule is the subject of recent increased interest as a consequence of the discrepancy between atmospheric observations and reported production and consumption. We use MIPAS/ENVISAT data (2002–2012) to estimate CCl₄ trends and lifetime. At 50 hPa we find a decline of about 30–35 % per decade. In the lower stratosphere our lifetime estimate is 47 (39–61) years.

This article deals with an investigation on the seasonal change in the sources of Saharan dust deposited in and off Mauritania using mineralogy. Onshore, dust was sourced from Western Sahara and a local source during summer and from Mauritania and Mali during winter. Offshore, dust was sourced from Mauritania, Mali and Libya during summer and from Western Sahara during winter. The outcome of the study has important implications for the reconstruction of past climates using dust deposits.