Abstract
Abstract. The MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) experiment took place in July 2009. The aim of this campaign was to study the aging and reactions of aerosol and gas-phase emissions in the city of Paris. Three ground-based measurement sites and several mobile platforms including instrument equipped vehicles and the ATR-42 aircraft were involved. We present here the variations in particle- and gas-phase species over the city of Paris, using a combination of high-time resolution measurements aboard the ATR-42 aircraft. Particle chemical composition was measured using a compact time-of-flight aerosol mass spectrometer (C-ToF-AMS), giving detailed information on the non-refractory submicron aerosol species. The mass concentration of black carbon (BC), measured by a particle absorption soot photometer (PSAP), was used as a marker to identify the urban pollution plume boundaries. Aerosol mass concentrations and composition were affected by air-mass history, with air masses that spent longest time over land having highest fractions of organic aerosol and higher total mass concentrations. The Paris plume is mainly composed of organic aerosol (OA), BC, and nitrate aerosol, as well as high concentrations of anthropogenic gas-phase species such as toluene, benzene, and NOx. Using BC and CO as tracers for air-mass dilution, we observe the ratio of ΔOA / ΔBC and ΔOA / ΔCO increase with increasing photochemical age (−log(NOx / NOy)). Plotting the equivalent ratios of different organic aerosol species (LV-OOA, SV-OOA, and HOA) illustrate that the increase in OA is a result of secondary organic aerosol (SOA) formation. Within Paris the changes in the ΔOA / ΔCO are similar to those observed during other studies in London, Mexico City, and in New England, USA. Using the measured SOA volatile organic compounds (VOCs) species together with organic aerosol formation yields, we were able to predict ~50% of the measured organics. These airborne measurements during the MEGAPOLI experiment show that urban emissions contribute to the formation of OA and have an impact on aerosol composition on a regional scale.
Highlights
It is necessary to characterize pollution arising from anthropogenic activities in large urban areas in order to understand its effects on health, as well as its influence on regional and global scale atmospheric chemistry and radiative forcing
A total of 8 research flights (RFs) with reliable C-ToF-AMS measurements were available aboard the ATR-42 from 13 to 29 July 2009 as part of the MEGAPOLI experiment
proton-transfer-reaction mass spectrometer (PTR-MS) data were available for a total of four flights and NOx / NOy measurements were available for five RFs
Summary
It is necessary to characterize pollution arising from anthropogenic activities in large urban areas in order to understand its effects on health, as well as its influence on regional and global scale atmospheric chemistry and radiative forcing. Freney et al.: Airborne measurements during the MEGAPOLI experiment and the evolution of aerosol chemical and physical properties as they are emitted from their source and diluted into regional air masses Some of these studies include MILAGRO (Mexico City emissions, DeCarlo et al, 2008), SOAR-1 (southern California, Docherty et al, 2011), and the EM25 campaign in London, UK (McMeeking et al, 2012). Each of these studies included a combination of several measurement sites situated at different distances from the centre of the city as well as mobile (airborne or vehicle) measurement platforms. Mobile measurement platforms provide a unique insight into the changes in the chemical and physical properties over both horizontal and vertical scales
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