A detailed case study of isoprene chemistry during the EASE96 Mace Head campaign

A detailed chemical mechanism has been used in conjunction with high-quality field measurements in order to assess the potential role of isoprene at a clean coastal Northern Hemisphere site. The importance of isoprene as a source of peroxy radicals, formaldehyde and ozone is discussed in some detail for a case study day (July 17 1996). Between 10:00 and 16:00 h GMT, isoprene accounts on average for 15% of the OH removal, yet is responsible for the production of about 30% of the HO2 radicals. Isoprene is also responsible for between 40 and 60% of the HCHO formation, and 20-40% of the 2 ppb h(-1) conversion of NO to NO2 by peroxy radicals. We discuss the significant time lag between HCHO formation and destruction, a time lag that must be accounted for in order to accurately calculate the rate of HO2 production from isoprene degradation, and the implications of the isoprene oxidation for atmospheric chemistry. (C) 2000 Elsevier Science Ltd. All rights reserved.