Direct Gas-Phase Formation of HCOOH through Reaction of Criegee Intermediates with Formaldehyde

Abstract Ozonolysis of isoprene is considered to be an important source of formic acid (HCOOH), but its underlying reaction mechanisms related to formic acid formation are poorly understood. Here, we report the kinetic and product studies of the reaction between the simplest Criegee intermediate (CH 2 OO) and formaldehyde (HCHO), both of which are the primary products formed in ozonolysis of isoprene. In addition to evaluation of the temperature and pressure dependencies of the rate coefficients, we determine the branching yields of the products HCOOH + HCHO and CO + H 2 O + HCHO by simultaneous determination of HCOOH and CO with synchronized two-color time resolved dual-comb spectroscopy. A high yield of HCOOH is obtained up to 40–50% under varied conditions. This work indicates that CH 2 OO + HCHO would play a critical role to explain high levels of atmospheric HCOOH, particularly in the upper troposphere and lower stratosphere.