Emissions of gaseous formic and acetic acids from major tree species in Japan

Abstract

Gaseous formic and acetic acids are directly emitted from vegetation and produced by the photooxidation of biogenic volatile organic compounds in the atmosphere. Gaseous formic and acetic acid emissions from trees have not been well studied in Japan and the Asian region, and to gain further knowledge in this respect, we measured the emissions of formic and acetic acid emissions together with isoprene and monoterpene emissions from 10 major forest tree species and 10 major road tree species. All of the measured trees were found to emit gaseous formic and acetic acids from their leaves, but not all species emitted isoprene or monoterpene. The emission rates of formic (0.05–1.3 μg gDW−1 h−1) and acetic (0.10–1.43 μg gDW−1 h−1) acids were similar to those of some trees in Europe but higher than those of tropical tree species. No monthly variations were found in the emission rates of formic and acetic acids, but the emission rates of isoprene and monoterpene showed clear monthly variations. We calculated the ratio of direct emissions to direct plus secondary production derived by the photooxidation of formic and acetic acids by isoprene and monoterpene (direct/total emission ratio) relating to major forest and road tree species in Japan. For isoprene and monoterpene emitters, the average values of the direct/total emission ratio of formic and acetic acids in August were 62% (range: 9.0–88%) and 64% (range: 6.2–90%), respectively. The contribution degree of the direct/total emission ratio differed depending on the isoprene and monoterpene emission rates. The findings are suggestive of the importance of both direct emissions of gaseous formic and acetic acids from trees and the secondary formation of these acids via isoprene and monoterpene photooxidation. The present study may be useful for improving the estimation accuracy of formic and acetic acid emissions from vegetation in future climate change and air quality studies.