AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Effect of the Urban Heat Island on Aerosol pH
MICHAEL BATTAGLIA JR., Sarah Douglas, Christopher Hennigan, University of Maryland, Baltimore County
Abstract Number: 140 Working Group: Aerosol Chemistry
Abstract The urban heat island (UHI) is a widely observed phenomenon whereby urban environments have higher temperature and lower relative humidity than surrounding suburban and rural areas. Temperature (T) and relative humidity (RH) are critical factors that affect the partitioning of semi-volatile species found in the atmosphere, such as nitric acid and ammonia. These species are inherently tied to aerosol pH, which is a key parameter driving some atmospheric chemical processes and environmental effects of aerosols. In this study, we characterized the effect of the UHI on aerosol pH in Baltimore, MD. The T and RH differences that define the UHI lead to substantial differences in aerosol liquid water (ALW) content for the same aerosol chemical composition. The ALW differences result in urban aerosol pH that is systematically lower (more acidic) than rural aerosol pH for identical aerosol composition. The UHI in Baltimore is most intense during the summer and at night, with differences of up to 1 pH unit predicted during these times. The UHI has been observed in cities of all sizes, so these results likely have broad implications for chemistry occurring in and around urban atmospheres globally.