Chemistry of daytime HOx radicals in marine boundary layer in the sea of Japan: Based on the ratio between the reactivity of HC and NOx

The ratio between the reactivity of HC and NOx,i.e.,Φ=ΣkOH+HCi[HCi]/(kOH+NO[NO]+kOH+NO2[NO2]),is used to study the chemistry of HOx radicals (HO2 and OH) in the marine boundary layer (MBL).Data analysis shows that HOx production and OH/HO2 ratio strongly depend on Φ.The OH radical concentration presents an ascending tendency in low Φ region but a declining one in high Φ region,while HO2 radical increases with increasing Φ under low Φ conditions but appears to be nearly constant with the variation of Φ under high Φ conditions.The observed OH/HO2 ratio shows a continuous decrease with the increase of Φ.Model studies are conducted to illuminate the behavior of HOx radicals in different Φ regions,and the results represent general agreement with the observed variations of HOx radicals and can well explain the observed behavior of HOx radicals.This study demonstrates that Φ could be used as an efficient parameter to ascertain the behavior of HOx radicals in the clean marine boundary layer.