Diurnal variation of OH radical and hydrocarbons in a polluted air mass during long-range transport in central Japan

Abstract

Abstract Long-range transport (LRT) of photochemical air pollution from the coastal area, with large emission sources to the inland mountainous region, occurs frequently in central Japan on clear summer days. Hydrocarbons and other pollutants were measured together with meteorological parameters along this route, and the diurnal variations of OH radical and hydrocarbons in the polluted air mass were investigated in relation with these photochemical reactions. At inland sampling sites, hydrocarbon concentrations in a polluted air mass decreased during LRT in the daytime. In particular, olefins were destroyed significantly because of more active photochemical reactions. From these destruction rates and/or O 3 formation rates the OH radical concentration was estimated and found to increase from 0.5 × 10 −7 in the morning to a maximum of 8.0 × 10 −7 ppm at midday. These values, as well as the diurnal variation, compared well with the numerical result of the comprehensive transport/reaction/removal model (Chang et al. , 1989, Atmospheric Environment 23 , 363–393, 1749–1773). The contribution of each hydrocarbon component to the total hydrocarbon destruction was also discussed.