A13F-05
Nighttime Chemistry and Morning Isoprene Drive Urban Ozone Downwind of a Major Deciduous Forest
Monday, 14 December 2015: 14:40
3010 (Moscone West)
Dylan B Millet1, Munkhbayar Baasandorj1, Lu Hu2, Dhruv Mitroo3, Jay Robert Turner3 and Brent J Williams3, (1)University of Minnesota Twin Cities, Minneapolis, MN, United States, (2)Harvard University, School of Engineering and Applied Sciences, Cambridge, MA, United States, (3)Washington University in St Louis, St. Louis, MO, United States
Abstract:
Isoprene is the predominant volatile organic compound emitted by vegetation. Isoprene emissions occur during daytime, when photo-oxidation is rapid and in the presence of nitrogen oxides (NOx) produces ozone and degrades air quality in polluted regions. Here we show in a city downwind of a deciduous forest that isoprene actually peaks at night, with nocturnal chemistry controlling the fate of that isoprene and the likelihood of a high-ozone episode the following day. When nitrate (NO3) radicals are suppressed, high isoprene persists through the night, providing photochemical fuel upon daybreak and a dramatic morning ozone peak. On nights with significant NO3, isoprene is removed before dawn; days with low morning isoprene then have lower ozone with a typical afternoon peak. This biogenic-anthropogenic coupling expands the daily high-ozone window and likely has opposite ozone-NOx response to what would otherwise be expected, with implications for exposure and air quality management in such areas.
