OH radical‐ initiated photooxidation of isoprene: An estimate of global CO production

Abstract

The OH radical‐ initiated photooxidation of isoprene has been investigated experimentally by a 6‐m 3 photochemical reaction chamber equipped with a long path length Fourier transform infrared spectrometer. In the presence of NO x , the major primary reaction products were methyl vinyl ketone, methacrolein, and formaldehyde. Their yields were in quantitative agreement with previous measurements. In the absence of NO x , the reaction mechanism was found to be quite different from that in the presence of NO x , and major reaction products observed in the infrared spectra were attributed to organic hydroperoxides. Based on the model experiments, the ultimate yield of CO was evaluated to be 60% on the carbon number basis in the presence of NO x and 23% in the absence of NO x . The CO yield in the real atmosphere was evaluated as 30% on the carbon number basis, and global annual CO production from isoprene was estimated to be 105 Tg C yr −1 . Together with a previous estimate of the CO production from terpenes, global CO production from natural hydrocarbons was evaluated to be 200±60 Tg C yr −1 .