Photochemical production of ozone in marine boundary layer in the sea of Japan: Results of the Rishiri Fall Experiment campaign

The Rishiri Fall Experiment (RISFEX ) campaign was performed in September 2003 at Rishiri island (45.07 N, 141.12 E, and 35 m asl) in the sea of Japan to investigate photochemical production of ozone in the marine boundary layer. Total peroxy radicals RO _x (HO₂ + RO₂) and NO _x (NO + NO₂) were measured together with other chemical species and physical parameters relevant to ozone production. The ozone production rate (P(O₃)) was estimated from measured peroxy radicals and was found to be highly variable between days, with 30-min averaged midday values varying from 0.2 to 1.7 ppbv/h (ppbv refers to part per billion by volume). The daytime mean P(O₃) for the air masses from relatively clean NE sector is close to zero, but significantly higher for air masses from more polluted W and SE sector, suggesting the impact of transport of pollutants on the remote local ozone production. The experimentally determined P(O₃) is compared with those derived from a time-dependent box model based on Regional Atmospheric Chemistry Modeling (RACM), and both the methods give the results generally in agreement. The model calculation shows that HO₂ + NO reaction contributes most to ozone production, ca. 60% at midday, followed by the reactions of CH₃O₂ and ISOP (peroxy radicals formed from isoprene) with NO which account for ca. 13% and 10% to ozone production, respectively, at noon. Sensitivity analysis indicates that the ozone production during the measurement period is within NO _x -limited regime.