Trends and analysis of ambient NO, NOy, CO, and ozone concentrations in Raleigh, North Carolina

Ambient concentrations of NO and NOy as well as O-3 and CO were measured during August 19 to September 1, 1991 in downtown Raleigh, North Carolina as a part of the Southern Oxidants Study-Southern Oxidants Research Program on Ozone Non-Attainment (SOS-SORP/ONA). These measurements were made in an effort to provide insight into the characteristics of nitrogen oxides and their role in the formation of ozone in the urban Southeast U.S. environment. NO and NOy, showed bimodal diurnal variations with peaks in the morning (06:00 - 08:00 EST) and in the late evening (21:00 - 23:00 EST). These peaks at this urban site correspond to the coupled effects of rush hour traffic and meteorological conditions (i.e., variation of mixing height and dispersion conditions). The overall average NO and NOy concentrations were found to be 6.1 +/- 5.4 ppbv (range: 0 to 70 ppbv) and 14.9 +/- 8.1 ppbv (range: 0.3 to 110 ppbv), respectively. Average daily maxima of NO and NOy (18.3 ppbv and 27.4 ppbv) occurred during the morning. O-3 showed a diurnal variation with a maximum in the afternoon between 14:00 and 16:00 EST; and a mean concentration 20 +/- 10 ppbv (range: 1 to 62 ppbv). Maximum O-3 and CO concentrations during weekdays result from NO and CO emitted from mobile sources during the morning rush hour. Background CO concentration at Raleigh was estimated to be - 470 +/- 52 ppbv. A linear correlation of r(2) = 0.53 between CO and NOy was observed. The ratio of CO to NOy (similar to 16) at the Raleigh site suggests that mobile sources are the major contributor to NO and NOy concentrations at the site. (C) 1997 Elsevier Science Ltd.