Airborne particulate matter (PM) negatively impacts air quality in cities throughout the world. An important fraction of PM is organic aerosol. We have evaluated and developed several new models for secondary organic aerosol (SOA), which is formed from the chemical processing of gaseous precursors. Using our model results, we have quantified important SOA sources and precursors and also identified possible model parameterizations that could be used for air quality predictions. Hide

We assess NO_x emission trends over Chinese cities based on satellite NO₂ observations using a method independent of chemical transport models. NO_x emissions over 48 Chinese cities have decreased significantly since 2011. Cities with different dominant emission sources (i.e. power, industrial, and transportation sectors) showed variable emission decline timelines that corresponded to the schedules for emission control in different sectors. Hide

An ozone mini-hole is a synoptic-scale region with strongly decreased total column ozone resulting from dynamical processes. Using total column measurements from the Ozone Monitoring Instrument and ozone profile measurements from the Microwave Limb Sounder, we evaluate the accuracy of mini-hole representation in five reanalyses. Hide

We investigated Arctic atmospheric bromine chemistry during March–April 2012 to improve understanding of the role of sea ice and cracks in sea ice (leads) in this phenomenon. We find that leads vertically redistribute reactive bromine but that open/re-freezing leads are not major direct reactive halogen sources. Surface ozone depletion affects the vertical distribution and amount of reactive halogens, and aerosol particles are necessary but not sufficient to maintain reactive bromine aloft. Hide

Multiday haze pollution in the Asian continental outflow region is affected by both local and regional sources. The temporal evolution of PM_2.5 inorganic species and organic compounds in Seoul, South Korea, and its upwind background site over the Yellow Sea shows the haze development sequentially by regional transport and local primary and secondary sources. Synoptic-scale weather systems and atmospheric blocking patterns play an important role in the dynamical evolution of the multiday haze. Hide

West Siberian peatlands occupy a large fraction of land area in the region, and yet little is known about their interaction with the atmosphere. We took the first measurements of CO₂ and energy surface balances over a typical bog of West Siberian middle taiga, in the vicinity of the Mukhrino field station (Khanty–Mansiysk). The May–August study in a wet year (2015) revealed a relatively large photosynthetic sink of CO₂ that was close to the high end of estimates at bog sites elsewhere. Hide

Ozone soundings in the troposphere from nine Arctic stations covering the period 1984–2014 have been analyzed. Stations with the best data coverage show a consistent and significant temporal variation with a maximum near 2005 followed by a decrease. Some significant changes are found in the annual cycle in agreement with the notion that the ozone summer maximum is appearing earlier in the year. Such changes in Arctic ozone in the free troposphere have not been reported before. Hide

We conducted temporal trend analysis of atmospheric NH₃ and NO₂ in China since 1980 based on emission data (during 1980–2010), satellite observations (for NH₃ since 2008 and for NO₂ since 2005) and atmospheric chemistry transport modeling (during 2008–2015). Our findings provide an overall insight into the temporal trends in both NO₂ and NH₃ since 1980, and the multivariate data used in this study have implications for estimating long-term Nr deposition datasets. Hide

Air quality is a major issue for megacities. Our paper looks at satellite measurements over Mexico City and Lagos of several trace gases gases related to air quality to determine the temporal and spatial variability of these gases, and it relates this variability to local conditions, such as topography, winds and biomass burning events. We find that, while Mexico City is known for severe pollution events, the levels of of pollution in Lagos are much higher and more persistent. Hide

We estimate how biofuel burning may contribute to cloud droplet numbers by modeling the evolution of the size and composition of each particle in a biofuel burning plume from emission until it reaches ambient temperature and humidity. Condensation of semi-volatile gases homogenizes composition so that particles without water affinity can form cloud droplets. Coagulation barely changes properties relevant to clouds, except for limiting the number of emitted particles or enhancing homogenization. Hide

Sea salt aerosol comes from the open ocean or the sea ice surface. In the polar regions, this opens up the possibility of reconstructing sea ice history using sea salt recorded in ice cores. We use a chemical transport model to demonstrate that the sea ice source of aerosol is important in the Arctic. For the first time, we simulate realistic Greenland ice core sea salt in a process-based model. The importance of the sea ice source increases from south to north across the Greenland ice sheet. Hide

The sources of PM_2.5 components exhibited short-term variabilities, and their contributions were identified in the Athabasca oil sands region. Much of the trace elements were found to originate from anthropogenic activities, i.e., oil sands upgrading and on- and off-road transportation. Some of these anthropogenic activities became better defined and understood only through highly time-resolved measurements, which can help guide further studies and policy decisions in the oil sands area. Hide

The global-scale patterns of subtropical marine boundary layer clouds are investigated with coincident NASA A-train satellite and reanalysis data. This study is novel in that all data are used at the finest spatial and temporal resolution possible. Our results are consistent with surface-based data and suggest that the combination of satellite and reanalysis data sets have potential to add to the global context of our understanding of the subtropical cumulus-dominated marine boundary layer. Hide

This study reports the distinct effects of street canyons on new particle formation (NPF) under warm or cold ambient temperature conditions because of on-road vehicle emissions; i.e., stronger condensation sinks are responsible for the reduced NPF in the springtime, but efficient nucleation and partitioning of gaseous species contribute to the enhanced NPF in the wintertime. The oxidization of biogenic organics is suggested to play an important role in growing new particles. Hide

In this study, studies on PM_2.5 chemical composition, source apportionment and its impact on aerosol optical properties across China are thoroughly reviewed, and historical emission control policies in China and their effectiveness in reducing PM_2.5 are discussed. Hide

Oxalic acid is an abundant and ubiquitous constituent in secondary organic aerosol (SOA) and can be an effective tracer for the oxidative processes leading to the formation of SOA. In this work photochemical reactions have a significant contribution to oxalic acid formation in summer, while in winter the formation of oxalic acid is closely associated with the oxidation of organic precursors in the aqueous phase. Hide

Aerosol-cloud interactions continue to contribute large uncertainties to our climate system understanding. In this study, we use near-global satellite and reanalysis data sets to predict marine liquid-water clouds by means of artificial neural networks. We show that on the system scale, lower-tropospheric stability and boundary layer height are the main determinants of liquid-water clouds. Aerosols show the expected impact on clouds but are less relevant than some meteorological factors. Hide

The aim of the study was to examine aged air masses being transported from the European continent towards Cyprus. Longer-lived oxygenated volatile organic compounds (OVOCs) such as methanol were mainly impacted by long-distance transport and showed higher values in air masses from eastern Europe than in a flow regime from the west. The impact of the transport through the marine boundary layer as well as the influence of the residual layer/free troposphere on OVOCs were studied. Hide

New particle formation (NPF) from gas-phase precursors is a process that is expected to drive the total number concentration of particles in the atmosphere. Here we use measurements performed simultaneously in Corsica, Crete and Mallorca to show that the spatial extent of the NPF events are several hundreds of kilometers large. Airborne measurements additionally show that nanoparticles in the marine atmosphere can either be of marine origin or from higher altitudes above the continent. Hide

Radar reflectivity is a valuable observational tool used to guide numerical weather model improvement. Biases in simulated reflectivity help identify potential errors in physical process and property representation in models. This study uniquely compares simulated and observed tropical convective systems to establish that a commonly documented high bias in radar reflectivity values at least partially results from the production of simulated ice particle sizes that are larger than observed. Hide

Using a model, we show that black carbon emissions from aircraft are most likely responsible for the observed high-altitude BC layers over the Indian region. Our analysis of model simulations and CALIPSO data shows that such aircraft-emitted BC layers can be vertically transported into the UTLS region upon their interaction with the underlying strong monsoonal convection. Such lifted BC layers, which intrude into the stratosphere, can potentially harm the stratospheric ozone layer. Hide

We present temporal and spatial δD distributions derived from IASI obtained above the North Atlantic in the vicinity of West Africa. We show that the seasonality of δD in the North Atlantic is closely associated with the influence of the Saharan heat low (SHL). We provide an interpretation of the temporal and spatial variations in δD and show that the interactions between the large-scale subsidence, the ITCZ, and the SHL can be disentangled thanks to the added information contained in δD. Hide

We evaluated the connection between DMS and the formation of aerosol particles in the Arctic atmosphere by analyzing multiple datasets of atmospheric DMS, aerosol particle size distributions and aerosol chemical composition that were collected at Ny-Ålesund, Svalbard (78.5° N, 11.8° E), during April–May 2015. The key finding from this research is that the contribution of biogenic DMS to the formation of aerosol particles was substantial during the phytoplankton bloom period. Hide

The influence on modeled max., mean and min. temperature over Europe of including aerosol–radiation–cloud interactions has been assessed for two case studies in 2010. Data were taken from an ensemble of online regional chemistry–climate models from EuMetChem COST Action. The results indicate that including these interactions clearly improves the spatiotemporal variability in the temperature signal simulated by the models, with implications for reducing the uncertainty in climate projections. Hide

We find that Asian anthropogenic sources are the largest contributors (~ 40 %) to surface BC in spring in the Arctic, inconsistent with previous studies which repeatedly identified sources of surface BC as anthropogenic emissions from Europe and Russia. It takes 12–17 days for Asian anthropogenic emissions to be transported to the Arctic surface. Additionally, a large fraction (40–65 %) of Asian contribution is in the form of chronic pollution on 1- to 2-month timescales. Hide