Toshimasa Ohara

Future prediction of surface ozone over east Asia using Models‐3 Community Multiscale Air Quality Modeling System and Regional Emission Inventory in Asia

[1]xa0Present and future tropospheric ozone (O3) concentrations over east Asia have been simulated by the Models-3 Community Multiscale Air Quality Modeling System (CMAQ) coupled with the Regional Emission Inventory in Asia (REAS) to predict surface O3 variations caused by future anthropogenic emissions changes. For future prediction, REAS provides three emission scenarios for China (the reference (REF), the policy succeed case (PSC), and the policy failure case (PFC) scenarios) and one emission scenario (the REF scenario) for the other countries. Simulated O3 concentration in summer was relatively high (70–80 ppbv in June and 65–75 ppbv in August) over the North China Plain in 2000. The projected REF emissions for 2020 (2020REF) enhance the monthly averaged O3 to 75–90 ppbv in June and 75–85 ppbv in August. The projected PSC emissions for 2020 (2020PFC), including a slight NOx reduction of –0.2 Tg (–2%) and a large NMVOC increase of 14.3 Tg (97%) for total Chinese emissions during 2000–2020, cause the monthly and annually averaged O3 concentrations to decrease by less than 2 ppbv in northeastern and central China. Over the North China Plain, the projected PFC emissions for 2020 (2020PFC) cause significant increases, more than 20 ppbv in the monthly averaged O3, and the O3 will be 85–105 ppbv in June and 80–95 ppbv in August for 2020. The 2020PFC also affect O3 increases in early summer in South Korea (14–18 ppbv increase for monthly average) and Japan (2–14 ppbv increase for monthly average) during 2000–2020 despite the slight NOx increase of 0.4 Tg (25%) in South Korea and the slight NOx reduction of –0.2 Tg (–10%) in Japan during 2000–2020. The pollutant in these regions seems to be transport from upwind source regions. These experiments show that over central eastern China at midday in June, the O3 concentration is largely affected by NOx emission increases but is insensitive to NMVOC emission increases.

IMPACT OF CHANGING CLIMATE AND EMISSIONS ON SURFACE OZONE DISTRIBUTIONS AND EVOLUTION

Socio-economic activities are rapidly increasing in many countries of Asia due to a population explosion. It is also suggested that greenhouse gases alter regional climate, causing changes in meteorological factors such as atmospheric circulation, precipitation, heat balance, and monsoon. These factors have potential impact on chemical transformation and long-range transport of air pollutants. To detect current and future changes in air quality, systematic observational networks with wide spatial and temporal coverage are highly required. In this work, ground-based measurement data of ozone and its precursors at ~20 remote sites from multiple monitoring networks including operational programs and collaborative research projects in East Asia are integrated. The idea and basis is that in-situ data are more accurate than satellite and sounding data, though its spatial coverage is limited. The intercomparisons of reference scales in each network make ambient data comparable to each other, and the integration of such traceable data allows us to cover wide latitudinal zones ranging from subtropical to boreal regions in the western Pacific within ~2% uncertainties. The data are further utili- zed to test multi-year simulations by a regional chemistry transport model (CMAQ). Interestingly, there are sizable interannual variations (and latitu- dinal dependences), suggesting that changes in regional meteorology (e.g., transport paths, patterns, and efficiency) and/or enhanced precursor emissions from biomass burning may have large contribution. Trends for 7 years are not visible at boundary layer sites, but are substantial at mountainous sites during continental outflow seasons, possibly due to increasing NOx emissions from East Asia. Implications to Meditteranean region are discussed in terms of emissions from biomass burning in present and expanding human acti- vities in future.