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

Abstract

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 ROx (HO2 + RO2) and NOx (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 NOx-limited regime.