A study of relationships between isoprene, its oxidation products, and ozone, in the Lower Fraser Valley, BC

As part of the Pacific '93 Oxidant Study that took place in the summer in the Lower Fraser Valley of British Columbia, we conducted measurements of isoprene, and its oxidation products methyl Vinyl ketone (MVK) and methacrolein (MACR) at a surface site about 40 km east of the city of Vancouver. Hourly measurements were conducted between 16 July and 10 August 1993. The data indicated evidence for substantial contributions of isoprene chemistry to the production of ozone during oxidant episodes in this region. Maximum concentrations of isoprene, MVK, and MACR were 5.3, 2.0, and 1.0 ppb, reap., for 4 August. Analysis of the relationship between MVK and O-3 during the oxidant episode period 1-6 August led to an estimated contribution of isoprene chemistry of ozone production of greater than or equal to 13%. The average measured ratio of MVK/MACR was about 1.9-2.0 in the daytime, compared to the published relative yield of 1.4. Comparison of the MVK and MACR measurements to those of organic nitrates led to the conclusion that there is a significant non-photochemical source of MVK and MACR in this urban area. (C) 1997 Elsevier Science Ltd.