Understanding atmospheric peroxyformic acid chemistry: observation, modeling and implication

Abstract. The existence and importance of peroxyformic acid (PFA) in the atmosphere has been under controversy. We present here, for the first time, the observation data for PFA from four field measurements carried out in China. These data provided powerful evidence that PFA can stay in the atmosphere, typically in dozens of pptv level. The relationship between PFA and other detected peroxides was examined. The results showed that PFA had a strong positive correlation with its homolog, peroxyacetic acid, due to their similar sources and sinks. Through an evaluation of PFA production and removal rates, we proposed that the reactions between peroxyformyl radical (HC(O)O₂) and formaldehyde or the hydroperoxyl radical (HO₂) were likely to be the major source and degradation into formic acid (FA) was likely to be the major sink for PFA. Based on a box model evaluation, we proposed that the HC(O)O₂ and PFA chemistry was a major source for FA under low NO_x conditions. Furthermore, it is found that the impact of the HC(O)O₂ and PFA chemistry on radical cycling was dependent on the yield of HC(O)O₂ radical from HC(O) + O₂ reaction. When this yield exceeded 50%, the HC(O)O₂ and PFA chemistry should not be neglected for calculating the radical budget. To make clear the exact importance of HC(O)O₂ and PFA chemistry in the atmosphere, further kinetic, field and modeling studies are required.