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The Southern Oxidant and Aerosol Study (SOAS) was a large field campaign during June-July 2013 in the southeast USA (Hidy et al., 2014; Hu et al., 2015; Carlton et al., 2018). Vast forested areas emitting large amounts of organic compounds and proximity to metropolitan areas present an ideal environment to investigate the influence of anthropogenic emissions on the biogenic secondary organic aerosol (SOA) formation. The main site of this study, located in rural Centreville, AL, was equipped with a wide variety of state-of-the-art analytical instruments. This project focuses on the source apportionment of the organic carbon (OC) fraction of ambient aerosol samples, through combination of radiocarbon (14C) data with positive matrix factorization information from online aerosol mass spectrometry measurements (AMS-PMF). Analysis of the long-lived radioactive isotope 14C is a unique source apportionment tool: it unambiguously separates fossil from non-fossil sources, as 14C has completely decayed in fossil fuels, whereas modern materials have the contemporary radiocarbon level (Szidat, 2009). 14C was measured for total carbon (TC) and elemental carbon (EC) (Zhang et al., 2012) from quartz filters that were collected at Centreville with daily resolution. This allowed the apportionment of fossil vs. non-fossil sources for EC and OC. Although OC mainly originated from non-fossil sources, a certain fraction was attributed to emissions from fossil sources. These results were compared with AMS-PMF data from a high-resolution time-of-flight AMS (Hu et al., 2015), which identified six different factors, i.e. biomass burning organic aerosol (BBOA), SOA formed through direct condensation of low-volatility oxidation products from isoprene (ISOPOOH-SOA), isoprene epoxydiols-derived SOA (IEPOX-SOA), low-oxidized oxygenated organic aerosol I, attributed to mostly biogenic sources (LO OOAI), low-oxidized OOA II, attributed mostly to anthropogenic sources (LO-OOAII) and more-oxidized OOA (MO-OOA). On average, the less well-understood fractions LO-OOAI, LO-OOAII and MO-OOA comprise ~3/4 of the total organic aerosol mass. 14C analysis of EC enables the distinction of sources of this carbonaceous aerosol fraction between fossil-fuel combustion (mainly from traffic) and biomass burning. It indicated a larger contribution from biomass burning compared to other source apportionment techniques or results from bottom-up emission inventories. The combination of 14C and AMS-PMF analysis provides the potential to apportion fossil vs. non-fossil sources for components for which the non-fossil fraction cannot by analyzed directly, such as SOA (Zotter et al., 2014). In this work, we present such results for the SOAS campaign based on Markov chain Monte Carlo calculations to gain more insight into the sources of SOA precursors. LO-OOAI, LO-OOAII and MO-OOA reveal different contributions of fossil and non-fossil sources, which allows a better understanding of these AMS-PMF factors. Carlton, A. M., et al. (2018), Bull. Am. Met. Soc., in press. Hidy, G. M., et al. (2014), Atmos. Chem. Phys., 14, 11893-11914. Hu, W. W., et al. (2015), Atmos. Chem. Phys., 15, 11807-11833. Szidat, S. (2009), Chimia, 63, 157-161. Zhang, Y. L., et al., (2012) Atmos. Chem. Phys., 12 (22), 10841-10856. Zotter, P., et al. (2014), J. Geophys. Res. Atmos., 119, 6818–6835.

Background\ud \ud Ship engine emissions are important with regard to lung and cardiovascular diseases especially in coastal regions worldwide. Known cellular responses to combustion particles include oxidative stress and inflammatory signalling.\ud \ud Objectives\ud \ud To provide a molecular link between the chemical and physical characteristics of ship emission particles and the cellular responses they elicit and to identify potentially harmful fractions in shipping emission aerosols.\ud \ud Methods\ud \ud Through an air-liquid interface exposure system, we exposed human lung cells under realistic in vitro conditions to exhaust fumes from a ship engine running on either common heavy fuel oil (HFO) or cleaner-burning diesel fuel (DF). Advanced chemical analyses of the exhaust aerosols were combined with transcriptional, proteomic and metabolomic profiling including isotope labelling methods to characterise the lung cell responses.\ud \ud Results\ud \ud The HFO emissions contained high concentrations of toxic compounds such as metals and polycyclic aromatic hydrocarbon, and were higher in particle mass. These compounds were lower in DF emissions, which in turn had higher concentrations of elemental carbon (“soot”). Common cellular reactions included cellular stress responses and endocytosis. Reactions to HFO emissions were dominated by oxidative stress and inflammatory responses, whereas DF emissions induced generally a broader biological response than HFO emissions and affected essential cellular pathways such as energy metabolism, protein synthesis, and chromatin modification.\ud \ud Conclusions\ud \ud Despite a lower content of known toxic compounds, combustion particles from the clean shipping fuel DF influenced several essential pathways of lung cell metabolism more strongly than particles from the unrefined fuel HFO. This might be attributable to a higher soot content in DF. Thus the role of diesel soot, which is a known carcinogen in acute air pollution-induced health effects should be further investigated. For the use of HFO and DF we recommend a reduction of carbonaceous soot in the ship emissions by implementation of filtration devices.

Although laboratory experiments have shown that organic compounds in both gasoline fuel and diesel engine exhaust can form secondary organic aerosol (SOA), the fractional contribution from gasoline and diesel exhaust emissions to ambient SOA in urban environments is poorly known. Here we use airborne and ground-based measurements of organic aerosol (OA) in the Los Angeles (LA) Basin, California made during May and June 2010 to assess the amount of SOA formed from diesel emissions. Diesel emissions in the LA Basin vary between weekdays and weekends, with 54% lower diesel emissions on weekends. Despite this difference in source contributions, in air masses with similar degrees of photochemical processing, formation of OA is the same on weekends and weekdays, within the measurement uncertainties. This result indicates that the contribution from diesel emissions to SOA formation is zero within our uncertainties. Therefore, substantial reductions of SOA mass on local to global scales will be achieved by reducing gasoline vehicle emissions.

The Mesolcina Valley campaign was an important part of the VOTALP project. Its main goals were the study of the effects of thermal wind systems on horizontal and vertical ozone transport over various distances, and on local production of ozone in an Alpine valley. The field measurements took place in the Mesolcina Valley in southern Switzerland in July and August 1996. The Mesolcina Valley is typical for the Alps for its size and its rural character, and contains an important traffic route. Ground-based and airborne instruments were deployed to obtain a four-dimensional chemical and physical picture of the valley atmosphere and the surroundings. Field measurements were complemented by numerical modeling studies. An overview of the campaign, its geographic background, and the measurement plan is given together with selected highlights of the results obtained so far. A synoptic-climatological approach tries to evaluate the representativeness of the observation days. It was found that during the campaign representative data for typical ozone days were collected, while extreme events did not occur. The main results of the campaign are that very high pollutant concentrations at the Alpine crests are the effect of advective, larger-scale transport, mainly from the Alpine forelands. The valley is very effective in pumping air into elevated layers during the day, with the slope winds probably carrying the bulk of the air volume to higher levels. Up to five times the valley volume may be exported during one upwind phase. Net local production is estimated to be approximately 3-8 ppb h high -1 of ozone, but seems to be compensated by dry deposition. This indicates that the Alpine valleys may be important net sinks of air pollutants, which may lead to negative impacts on the Alpine ecosystems.

During winter 2013, extremely high concentrations (i.e., 4–20 times higher than the World Health Organization guideline) of PM2.5 (particulate matter with an aerodynamic diameter < 2.5 μm) mass concentrations (24 h samples) were found in four major cities in China including Xi'an, Beijing, Shanghai and Guangzhou. Statistical analysis of a combined data set from elemental carbon (EC), organic carbon (OC), 14C and biomass-burning marker measurements using Latin hypercube sampling allowed a quantitative source apportionment of carbonaceous aerosols. Based on 14C measurements of EC fractions (six samples each city), we found that fossil emissions from coal combustion and vehicle exhaust dominated EC with a mean contribution of 75 ± 8% across all sites. The remaining 25 ± 8% was exclusively attributed to biomass combustion, consistent with the measurements of biomass-burning markers such as anhydrosugars (levoglucosan and mannosan) and water-soluble potassium (K+). With a combination of the levoglucosan-to-mannosan and levoglucosan-to-K+ ratios, the major source of biomass burning in winter in China is suggested to be combustion of crop residues. The contribution of fossil sources to OC was highest in Beijing (58 ± 5%) and decreased from Shanghai (49 ± 2%) to Xi'an (38 ± 3%) and Guangzhou (35 ± 7%). Generally, a larger fraction of fossil OC was from secondary origins than primary sources for all sites. Non-fossil sources accounted on average for 55 ± 10 and 48 ± 9% of OC and total carbon (TC), respectively, which suggests that non-fossil emissions were very important contributors of urban carbonaceous aerosols in China. The primary biomass-burning emissions accounted for 40 ± 8, 48 ± 18, 53 ± 4 and 65 ± 26% of non-fossil OC for Xi'an, Beijing, Shanghai and Guangzhou, respectively. Other non-fossil sources excluding primary biomass burning were mainly attributed to formation of secondary organic carbon (SOC) from non-fossil precursors such as biomass-burning emissions. For each site, we also compared samples from moderately to heavily polluted days according to particulate matter mass. Despite a significant increase of the absolute mass concentrations of primary emissions from both fossil and non-fossil sources during the heavily polluted events, their relative contribution to TC was even decreased, whereas the portion of SOC was consistently increased at all sites. This observation indicates that SOC was an important fraction in the increment of carbonaceous aerosols during the haze episode in China.

Determining the contribution of wood smoke to air pollution in large cities such as London is becoming increasingly important due to the changing nature of domestic heating in urban areas. During winter, biomass burning emissions have been identified as a major cause of exceedances of European air quality limits. The aim of this work was to quantify the contribution of biomass burning in London to concentrations of PM2:5 and determine whether local emissions or regional contributions were the main source of biomass smoke. To achieve this, a number of biomass burning chemical tracers were analysed at a site within central London and two sites in surrounding rural areas. Concentrations of levoglucosan, elemental carbon (EC), organic carbon (OC) and KC were generally well correlated across the three sites. At all the sites, biomass burning was found to be a source of OC and EC, with the largest contribution of EC from traffic emissions, while for OC the dominant fraction included contributions from secondary organic aerosols, primary biogenic and cooking sources. Source apportionment of the EC and OC was found to give reasonable estimation of the total carbon from non-fossil and fossil fuel sources based upon comparison with estimates derived from 14C analysis. Aethalometer-derived black carbon data were also apportioned into the contributions frombiomass burning and traffic and showed trends similar to those observed for EC. Mean wood smoke mass at the sites was estimated to range from 0.78 to 1.0 μgm-3 during the campaign in January–February 2012. Measurements on a 160m tower in London suggested a similar ratio of brown to black carbon (reflecting wood burning and traffic respectively) in regional and London air. Peaks in the levoglucosan and KC concentrations were observed to coincide with low ambient temperature, consistent with domestic heating as a major contributing local source in London. Overall, the source of biomass smoke in London was concluded to be a background regional source overlaid by contributions from local domestic burning emissions. This could have implications when considering future emission control strategies during winter and may be the focus of future work in order to better determine the contributing local sources.

Secondary organic aerosol (SOA) accounts for a significant fraction of ambient tropospheric aerosol and a detailed knowledge of the formation, properties and transformation of SOA is therefore required to evaluate its impact on atmospheric processes, climate and human health. The chemical and physical processes associated with SOA formation are complex and varied, and, despite considerable progress in recent years, a quantitative and predictive understanding of SOA formation does not exist and therefore represents a major research challenge in atmospheric science. This review begins with an update on the current state of knowledge on the global SOA budget and is followed by an overview of the atmospheric degradation mechanisms for SOA precursors, gas-particle partitioning theory and the analytical techniques used to determine the chemical composition of SOA. A survey of recent laboratory, field and modeling studies is also presented. The following topical and emerging issues are highlighted and discussed in detail: molecular characterization of biogenic SOA constituents, condensed phase reactions and oligomerization, the interaction of atmospheric organic components with sulfuric acid, the chemical and photochemical processing of organics in the atmospheric aqueous phase, aerosol formation from real plant emissions, interaction of atmospheric organic components with water, thermodynamics and mixtures in atmospheric models. Finally, the major challenges ahead in laboratory, field and modeling studies of SOA are discussed and recommendations for future research directions are proposed.