Concentration, sources and ozone formation potential of volatile organic compounds (VOCs) during ozone episode in Beijing

Concentrations of carbonyl compounds and non-methane hydrocarbons (NMHCs) were measured at an urban site in Beijing from 16 to 19 August 2006 during an ozone episode. Of the six days monitored there were four days of which the 1-h maximum ozone concentration exceeding 160μg m− 3 the Ambient Air Quality Standard (GB 3095—1996). Measurements of a variety of trace gases (O3, NOx, CO, volatile organic compounds (VOCs)) were carried out simultaneously. Principal component analysis/absolute principal component scores (PCA/APCS) was used to identify the dominant emission sources and evaluate their contribution to NMHCs and carbonyls. The possible sources for NMHCs in Beijing are combustion sources, solvent usage and biogenic sources, and for carbonyls are vehicle emission, cooking and biogenic sources. The ratios of NMHCs/NOx and Carbonyls/NOx are 11.8 ± 3.9 and 2.7 ± 0.8, which indicate the production of O3 is controlled by both VOCs and NOx. The VOCs data were used to estimate the potential amount of ozone formation in Beijing. Based on the MIR scale, the leading contributors to O3 formation in Beijing are formaldehyde, xylenes, trimethylbenzenes, acetaldehyde and propene which account for 56% of the total ozone formation potential. However, ranking by Prop-Equiv, isoprene, xylenes, formaldehyde, trimethylbenzenes and propene are top 5 VOCs which account for 43% of the total Prop-Equiv concentration. isoprene shows negative and poor correlation with CO and ethyne, however, it shows good correlation with temperature (R2 = 0.63), which means it is mostly biogenic rather than anthropogenic. On average, isoprene accounts for 14% of the total Prop-Equiv concentration and 3% of total ozone formation potentials.