The photochemical formation of alkyl nitrates (RONO2) and their impact on ozone (O3) formation were investigated using a Photochemical Box Model incorporating the Master Chemical Mechanism (PBM-MCM). The model was constrained with field measurement data collected on selected O3 episode days at Tai O, a rural-coastal site in southwestern Hong Kong, from August 2001-December 2002. The in-situ observations showed that the sum of C1-C5 RONO2 varied from 30.7 ± 14.8 pptv in spring to 120.7 ± 10.4 pptv in autumn, of which 2-butyl nitrate dominated with the highest average concentration of 30.8 ± 2.6 pptv. Model simulations indicated that the pathway of CH3O reacting with NO2, proposed in our previous study, made minor contributions (11.3 ± 0.7%) to methyl nitrate formation. Indeed, 51.8 ± 3.1% and 36.5 ± 6.3% of the methyl nitrate was attributed to the reaction of CH3O2+NO and to oceanic emissions/biomass burning, respectively. For the C2-C5 alkyl nitrates, the contribution of photochemical formation increased with increasing carbon number, ranging from 64.4 ± 4.0% for ethyl nitrate (EtONO2) to 72.6 ± 4.2% for 2-pentyl nitrate (2-PenONO2), while the contribution of oceanic emissions/biomass burning decreased from 35.1 ± 6.5% for EtONO2 to 26.8 ± 6.8% for 2-PenONO2. Model simulations of photochemical O3 levels influenced by RONO2 chemistry showed that the formation of methyl-, ethyl-, i-propyl-, n-propyl-, 2-butyl-, 2-pentyl-, and 3-pentyl-nitrates led to O3 reduction of 0.05 ± 0.03, 0.05 ± 0.03, 0.06 ± 0.02, 0.02 ± 0.02, 0.18 ± 0.04, 0.09 ± 0.02 and 0.06 ± 0.02 ppbv, respectively, with an average reduction rate of 11.0 ± 3.2 ppbv O3 per 1 ppbv RONO2 formation. The C1-C5 RONO2 constituted 18.6 ± 1.9% of the entire RONO2, and had a nitrogen reserve of 4.1 ± 0.2%, implying their potential influence on O3 production in downwind areas.Department of Civil and Environmental Engineerin
Is data on this page outdated, violates copyrights or anything else? Report the problem now and we will take corresponding actions after reviewing your request.