Seasonal variation of biogenic VOC emissions above a mixed hardwood forest in northern Michigan

Fluxes of biogenic volatile organic compounds (VOCs) were measured at a hardwood forest in northern Michigan (UMBS, Prophet research site) over the course of the growing and senescing season. Methanol, acetaldehyde, acetone and isoprene were found to be the most abundant biogenic VOCs with maximum fluxes (mixing ratios in ppbv) of 2.0 mg m(-2) h(-1) (21.0), 1.0 mg m(-2) h(-1) (2.7), 1.6 mg m(-2) h(-1) (5.6) and 7.6 mg m(-2) h(-1) (6), respectively. The emission patterns show distinct seasonal changes and indicate a spring peak for methanol due to rapid leaf expansion and a fall peak for acetone and acetaldehyde most likely attributed to senescing and decaying biomass; isoprene emissions peaked as expected in the summer. We estimate potential source strengths of 8.9 Tg (C) y(-1) methanol, 2.7 Tg (C) y(-1) acetaldehyde and 7.0 Tg (C) y(-1) acetone for deciduous temperate forests, which is a substantial contribution to the global atmospheric VOC budget.