Diagnosis of Photochemical Ozone Production Rates and Limiting Factors in Continental Outflow Air Masses Reaching Fukue Island, Japan: Ozone-Control Implications

Yugo Kanaya,Xiaole Pan,Susumu Nozoe,Hitoshi Irie,Yuichi Komazaki,Hiroshi Tanimoto,Yoko Yokouchi,Satoshi Inomata,Fumikazu Taketani,Hisahiro Takashima

doi:10.4209/aaqr.2015.04.0220

Abstract

ABSTRACTAsian continental outflow air masses reach western Japan in the springtime, carrying high levels of ozone produced over the Asian continent, and facilitating in-situ production. In this study, in-situ production was highlighted; the rate and limiting factors of net ozone production were diagnosed at Fukue Island, a remote island west of Japan, on 17 days during May–June 2009, when the continental outflow air mass arrived, using an observation-based modeling approach. The average ozone production was estimated to be 6.8 ppb per day. Information on the chemical status of the arriving air mass is important, because it affects how further ozone production in the air mass occurs after precursor addition from Japanese domestic emissions. The main limiting factor of ozone production for such air masses was usually nitrogen oxides (NOx), suggesting that domestic NOx emission control is important in reducing further ozone production. Volatile organic compounds (VOCs) also increased the ozone production rate, and occasionally (14% of time) became the dominant controlling factor. This analysis implies that the VOC reduction legislation recently enacted by the Japanese government should be effective. VOC-limited conditions occurred particularly when the air mass traveled within 6‒8 h, via the Korean Peninsula. The uncertainty in the radical chemistry mechanism governing ozone production had a non-negligible impact, but the main conclusion relevant to policy was not altered. When chain termination was augmented by HO2 + NO/NO2 reactions in the presence of H2O and by heterogeneous loss of HO2 on aerosol particle surfaces, as recently verified or hypothesized, the daily ozone production rate decreased by up to 24%, and the fraction of hours when the VOC-limited condition occurred varied from 14% to 13‒26%.

Highlights

The health issues related to elevated concentrations of tropospheric ozone over the Pacific Rim region of East Asia are of concern, because photochemical production of ozone has recently been strengthened by increased emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs)
NOx was probably emitted in the continental region, Impact of Modified Radical Chemistry We studied how the recently proposed HO2 radical reaction pathway, which is not included in the standard tropospheric chemistry mechanism, influenced the ozone production rates
The observation-based model (OBM) approach used to assess the in-situ ozone production rates and regimes in the continental outflow air masses suggested that production on previous days over the continent, and insitu or in-travel production was as much as 6.8 ppb per day, and raised the ozone levels

Summary

Introduction

The health issues related to elevated concentrations of tropospheric ozone over the Pacific Rim region of East Asia are of concern, because photochemical production of ozone has recently been strengthened by increased emissions of nitrogen oxides (NOx) and volatile organic compounds (VOCs). In-situ production was highlighted; the rate and limiting factors of net ozone production were diagnosed at Fukue Island, a remote island west of Japan, on 17 days during May–June 2009, when the continental outflow air mass arrived, using an observation-based modeling approach.

Results

Conclusion