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 measur ed during August 19 to September 1, 1991 in downtown Raleigh, North Ca rolina as a part of the Southern Oxidants Study-Southern Oxidants Rese arch Program on Ozone Non-Attainment (SOS-SORP/ONA). These measurement s were made in an effort to provide insight into the characteristics o f nitrogen oxides and their role in the formation of ozone in the urba n Southeast U.S. environment. NO and NOy, showed bimodal diurnal varia tions with peaks in the morning (06:00 - 08:00 EST) and in the late ev ening (21:00 - 23:00 EST). These peaks at this urban site correspond t o the coupled effects of rush hour traffic and meteorological conditio ns (i.e., variation of mixing height and dispersion conditions). The o verall 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 pp bv), respectively. Average daily maxima of NO and NOy (18.3 ppbv and 2 7.4 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 mea n concentration 20 +/- 10 ppbv (range: 1 to 62 ppbv). Maximum O-3 and CO concentrations during weekdays result from NO and CO emitted from m obile sources during the morning rush hour. Background CO concentratio n at Raleigh was estimated to be - 470 +/- 52 ppbv. A linear correlati on 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 a re the major contributor to NO and NOy concentrations at the site. (C) 1997 Elsevier Science Ltd.