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Abstract. Isoprene-derived secondary organic aerosol (iSOA) is a significantcontributor to organic carbon (OC) in some forested regions, such astropical rainforests and the Southeastern US. However, its contribution toorganic aerosol in urban areas that have high levels of anthropogenicpollutants is poorly understood. In this study, we examined the formation ofanthropogenically influenced iSOA during summer in Beijing, China. Localisoprene emissions and high levels of anthropogenic pollutants, inparticular NOx and particulate SO42-, led to the formation ofiSOA under both high- and low-NO oxidation conditions, with significantheterogeneous transformations of isoprene-derived oxidation products toparticulate organosulfates (OSs) and nitrooxy-organosulfates (NOSs).Ultra-high-performance liquid chromatography coupled to high-resolution massspectrometry was combined with a rapid automated data processing techniqueto quantify 31 proposed iSOA tracers in offline PM2.5 filterextracts. The co-elution of the inorganic ions in the extracts caused matrixeffects that impacted two authentic standards differently. The averageconcentration of iSOA OSs and NOSs was 82.5 ng m−3, which was around 3 timeshigher than the observed concentrations of their oxygenated precursors(2-methyltetrols and 2-methylglyceric acid). OS formation was dependant onboth photochemistry and the sulfate available for reactive uptake, as shown by astrong correlation with the product of ozone (O3) and particulatesulfate (SO42-). A greater proportion of high-NO OS products wereobserved in Beijing compared with previous studies in less pollutedenvironments. The iSOA-derived OSs and NOSs represented 0.62 %of the oxidized organic aerosol measured by aerosol mass spectrometry on average, butthis increased to ∼3 % on certain days. These resultsindicate for the first time that iSOA formation in urban Beijing is stronglycontrolled by anthropogenic emissions and results in extensive conversion toOS products from heterogenous reactions. 

Abstract. Anthropogenic secondary organic aerosol (ASOA), formed from anthropogenicemissions of organic compounds, constitutes a substantial fraction of themass of submicron aerosol in populated areas around the world andcontributes to poor air quality and premature mortality. However, theprecursor sources of ASOA are poorly understood, and there are largeuncertainties in the health benefits that might accrue from reducinganthropogenic organic emissions. We show that the production of ASOA in 11urban areas on three continents is strongly correlated with the reactivityof specific anthropogenic volatile organic compounds. The differences inASOA production across different cities can be explained by differences inthe emissions of aromatics and intermediate- and semi-volatile organiccompounds, indicating the importance of controlling these ASOA precursors.With an improved model representation of ASOA driven by the observations,we attribute 340 000 PM2.5-related premature deaths per year to ASOA, which isover an order of magnitude higher than prior studies. A sensitivity casewith a more recently proposed model for attributing mortality to PM2.5(the Global Exposure Mortality Model) results in up to 900 000 deaths. Alimitation of this study is the extrapolation from cities with detailedstudies and regions where detailed emission inventories are available toother regions where uncertainties in emissions are larger. In addition tofurther development of institutional air quality management infrastructure,comprehensive air quality campaigns in the countries in South and CentralAmerica, Africa, South Asia, and the Middle East are needed for furtherprogress in this area. 

Abstract. The science guiding the EUREC4A campaign and its measurements is presented. EUREC4A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic – eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC4A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC4A explored – from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation – are presented along with an overview of EUREC4A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement.