Trends and analysis of ambient NO, NO(y), CO, and ozone concentrations in Raleigh, North Carolina

Ambient concentrations of NO and NO(y) as well as O3 and CO were measured dining August 19 to September 1, 1991 in downtown Raleigh, North Carolina as apart 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 NO(y) 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 NO(y) 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 NO(y) (18.3 ppbv and 27.4 ppbv) occurred during the morning. O3 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 O3 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 r2 = 0.53 between CO and NO(y) was observed. The ratio of CO to NO(y) (~16) at the Raleigh site suggests that mobile sources are the major contributor to NO and NO(y) concentrations at the site.

Duke Scholars

Author William Chameides Earth and Climate Sciences