Direct measurements of HOx radicals in the marine boundary layer: Testing the current tropospheric chemistry mechanism

Yugo Kanaya, Hajime Akimoto

The Chemical Record, 2, 199-211, 2002.


OH and HO2 radicals, atmospheric detergents, and the reservoir thereof, play central roles in tropospheric chemistry. In spite of their importance, we had no choice but trust their concentrations that are predicted by modeling studies based on known chemical processes. However, recent direct measurements of these radicals have enabled us to test and revise our knowledge of the processes by comparing the predicted and observed values of the radical concentrations. We developed a laser-induced fluorescence instrument and successfully observed OH and HO2 at three remote islands of Japan (Oki Island, Okinawa Island, and Rishiri Island). At Okinawa Island, the observed daytime level of HO2 agreed closely with the model estimates , suggesting that the photochemistry at Okinawa is well described by the current chemistry mechanism. At Rishiri Island, in contrast, the observed daytime level of HO2 was consistently much lower than the calculated values. We proposed that iodine chemistry, usually not incorporated into the mechanism, is at least partly responsible for the discrepancy in the results. At night, HO2 was detected at levels greater than 1 pptv at all three islands, suggesting the presence of dark processes that produce radicals. We showed that ozone reactions with unsaturated hydrocarbons, including monoterpenes, could significantly contribute to radical production.