h i g h l i g h t sAviation is globally growing (þ5% y À1 ) mainly driven by developing countries. Airport operations cause an increase in ground-level pollution. Chemical and physical properties of the emitted gases and particles are reviewed. An overview of other additional sources within airports is provided. Future research needs on aircraft emissions are highlighted. a b s t r a c tCivil aviation is fast-growing (about þ5% every year), mainly driven by the developing economies and globalisation. Its impact on the environment is heavily debated, particularly in relation to climate forcing attributed to emissions at cruising altitudes and the noise and the deterioration of air quality at groundlevel due to airport operations. This latter environmental issue is of particular interest to the scientific community and policymakers, especially in relation to the breach of limit and target values for many air pollutants, mainly nitrogen oxides and particulate matter, near the busiest airports and the resulting consequences for public health. Despite the increased attention given to aircraft emissions at groundlevel and air pollution in the vicinity of airports, many research gaps remain. Sources relevant to air quality include not only engine exhaust and non-exhaust emissions from aircraft, but also emissions from the units providing power to the aircraft on the ground, the traffic due to the airport ground service, maintenance work, heating facilities, fugitive vapours from refuelling operations, kitchens and restaurants for passengers and operators, intermodal transportation systems, and road traffic for transporting people and goods in and out to the airport. Many of these sources have received inadequate attention, despite their high potential for impact on air quality. This review aims to summarise the state-of-the-art research on aircraft and airport emissions and attempts to synthesise the results of studies that have addressed this issue. It also aims to describe the key characteristics of pollution, the impacts upon global and local air quality and to address the future potential of research by highlighting research needs. Atmospheric Environment 95 (2014) 409e455 x Partitioning coefficient M. Masiol, R.M. Harrison / Atmospheric Environment 95 (2014) 409e455 410

Rationale: Fine particulate matter air pollution of 2.5 μm or less in diameter (PM 2.5 ) has been associated with an increased risk of respiratory disease, but assessments of specific respiratory infections in adults are lacking. Objectives: To estimate the rate of respiratory infection healthcare encounters in adults associated with acute increases in PM 2.5 concentrations. Methods: Using case–crossover methods, we studied 498,118 adult New York State residents with a primary diagnosis of influenza, bacterial pneumonia, or culture-negative pneumonia upon hospitalization or emergency department (ED) visit (2005–2016). We estimated the relative rate of healthcare encounters associated with increases in PM 2.5 in the previous 1–7 days and explored differences before (2005–2007), during (2008–2013), and after (2014–2016) implementation of air quality policies and economic changes. Results: Interquartile range increases in PM 2.5 over the previous 7 days were associated with increased excess rates (ERs) of culture-negative pneumonia hospitalizations (2.5%; 95% confidence interval [CI], 1.7–3.2%) and ED visits (2.5%; 95% CI, 1.4–3.6%), and increased ERs of influenza ED visits (3.9%; 95% CI, 2.1–5.6%). Bacterial pneumonia hospitalizations, but not ED visits, were associated with increases in PM 2.5 and, though imprecise, were of a similar magnitude to culture-negative pneumonia (Lag Day 6 ER, 2.3%; 95% CI, 0.3–4.3). Increased relative rates of influenza ED visits and culture-negative pneumonia hospitalizations were generally larger in the “after” period ( P < 0.025 for both outcomes), compared with the “during” period, despite reductions in overall PM 2.5 concentrations. Conclusions: Increased rates of culture-negative pneumonia and influenza were associated with increased PM 2.5 concentrations during the previous week, which persisted despite reductions in PM 2.5 from air quality policies and economic changes. Though unexplained, this temporal variation may reflect altered toxicity of different PM 2.5 mixtures or increased pathogen virulence.

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Oxidized organic aerosol (OOA) is a major component of ambient particulate matter, substantially impacting climate, human health, and ecosystems. OOA is readily produced in the presence of sunlight, and requires days of photooxidation to reach the levels observed in the atmosphere. High concentrations of OOA are thus expected in the summer; however, our current mechanistic understanding fails to explain elevated OOA during wintertime periods of low photochemical activity that coincide with periods of intense biomass burning. As a result, atmospheric models underpredict OOA concentrations by a factor of 3 to 5. Here we show that fresh emissions from biomass burning exposed to NO2 and O3 (precursors to the NO3 radical) rapidly form OOA in the laboratory over a few hours and without any sunlight. The extent of oxidation is sensitive to relative humidity. The resulting OOA chemical composition is consistent with the observed OOA in field studies in major urban areas. Additionally, this dark chemical processing leads to significant enhancements in secondary nitrate aerosol, of which 50 to 60% is estimated to be organic. Simulations that include this understanding of dark chemical processing show that over 70% of organic aerosol from biomass burning is substantially influenced by dark oxidation. This rapid and extensive dark oxidation elevates the importance of nocturnal chemistry and biomass burning as a global source of OOA.