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 40–60% 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.