Diurnal profiles of isoprene, methacrolein and methyl vinyl ketone at an urban site in Hong Kong: Fid-Bau Portal

Diurnal profiles of isoprene, methacrolein and methyl vinyl ketone at an urban site in Hong Kong

Cheung, K. / Guo, H. / Ou, J.M. / Simpson, I.J. / Barletta, B. / Meinardi, S. / Blake, D.R.

Abstract Methacrolein (MACR) and methyl vinyl ketone (MVK) are major oxidation products of isoprene, but they also have primary emissions in urban environments, for example from fuel use. To examine whether MACR and MVK could be used as a direct measurement of the oxidation rate of isoprene in an urban setting, the diurnal variations of isoprene, MACR and MVK were characterized at an urban site in Hong Kong from September to November, 2010. Ozone (O3), carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen oxides (NOx) were simultaneously monitored. The average isoprene mixing ratio was 252 ± 204 pptv, with a bell-shaped distribution observed on most sampling days. Higher levels of isoprene were recorded in the beginning of the sampling period, when the temperature was higher. The average mixing ratios of MACR and MVK were 101 ± 85 pptv and 175 ± 131 pptv, respectively. While isoprene, MACR and MVK experienced peak concentrations from 11 a.m. to 3 p.m., increased levels of MACR and MVK during the morning rush hour did not coincide with isoprene. The low associations between isoprene and MACR/MVK suggest that either MACR/MVK were not formed from local isoprene oxidation and/or they could partly originate from primary emissions such as fuel evaporation or combustion. Statistical analyses of linear regression and positive matrix factorization revealed that approximately 20–29% of the measured MACR and MVK was associated with biogenic emissions, and 55–71% was impacted by vehicular emissions, particularly during morning rush hours. Since MACR and MVK originated from both primary emissions and biogenic emissions at this urban site, they can therefore overestimate the actual rate of isoprene oxidation and its contribution to O3 production in urban areas with strong primary emissions.

Highlights • Isoprene primarily originated from local biogenic emissions. • Higher isoprene levels were observed on days when average daily temperature was above 30 °C. • Traffic emissions and biogenic emissions were the major contributors to MACR/MVK. • The use of MACR/MVK to represent the isoprene oxidation rate is inappropriate in urban Hong Kong.