The Numerical Modeling Analysis Of Tropospheric Ozone Sources And Budgets Over East Asia And Pacific Ocean

This study uses the ozone (O3) observation data from EANET, WDCGG, TOMS, OMI, TES, and so on, combined with the global atmospheric chemical transport model MOZART-4, confirmed the seasonal and interannual variation of ozone and its sources in East Asia and other regions in the globe. The impacts of East Asia monsoon and ENSO on ozone also are discussed.The evaluation of the model shows that the model-simulated O3 and its precursors agree well with observed values in the troposphere. The analyses of O3 budget at surface show the values of processes flux are relatively low, and the chemistry is net loss of O3 over clean background regions (most in ocean). The contributions from different areas indicate the sources of surface O3 are from inside of troposphere, and the contributions of stratospheric O3 are relatively low. Over polar and clean region, the contributions of stratospheric O3 account for the O3 seasonal variations.The large latitudinal gradient in O3 with a maximum of 52 ppbv over the marine boundary layer around 35°N during the spring was mainly due to chemistry; meanwhile, advection was found to weaken the gradient. The contribution of stratospheric O3 was ranked second (20%) to the local contribution (25%) in Japan and the Korean Peninsula near 35°N. The rate of O3 export from China’s boundary layer was the highest (30%) in low latitudes and decreased with increasing latitude, while the contribution of North America and Europe increased with increasing latitude, from 10% in lower latitudes to 24% in higher latitudes.In the boundary layer of the northeastern Qinghai-Tibetan Plateau, in situ photochemistry and the advectional transport of photochemical produced O3 in East Asia and Europe-Africa are mainly responsible for O3 summer maximum. The contribution of Qinghai-Tibet Plateau O3 was 10.2 parts per billion by volume (ppbv) in summer. The total contribution of O3 transport from eastern China, Japan and Korean Peninsula and Europe-Africa O3 was 16.0 ppbv in summer. Deep convection caused a decrease of O3 in the upper troposphere at Mt. Waliguan, while it caused an increase in the lower atmosphere. The effect of lightning on O3 at Mt. Waliguan was concentrated in the upper troposphere in summer with a maximum of-10.0 ppbv. The contributions of deep convection and lightning to surface O3 at Mt. Waliguan were both-2.0 ppbv in summer. They are not the key contributors to the O3 summer maximum.Asia-Pacific monsoon significantly influence the seasonal and inter-annual variation of O3. The differences of anthropogenic emissions and zonal winds in meridional directions cause a pollutants’transition zone at 20°-30°N. The onset of summer monsoons with a northward migration of the rain belt leads the transition zone to drift north. In years with an early onset of summer monsoons, strong inflows of clean oceanic air lead to low ozone at polluted oceanic sites near the continent, while strong outflows from the continent exist, resulting in high levels of O3 over remote portions of the Asia-Pacific Ocean. The reverse is true in years when the summer monsoon onset is late. Advection appears to play a key role in the impact of the summer monsoon onset on the inter-annual variation of O3 in spring.Temporal correlation coefficients between Nino3.4 anomalies and gridded O3 anomalies from observation and simulation both show an asymmetrical dipole structure which present positive correlation (R=0.6) in western Pacific region including Indonesia (WP) and negative correlation (R=-0.5) in central and eastern Pacific region (CP and EP). The variations of tropospheric column O3 anomalies (TCOA) are different in Canonical El Nino (CEN) and El Nino Modoki (ENM) events. The absolute values of TCOA are larger than that in ENM in most regions, and the area covered by positive TCOA is much wider. The duration of ENM is shorter than that of CEN. And the area covered by negative TCOA is relatively wide. La Nina events show a dipole in TCOA which is reversed from that of El Nino events. In CEN, anomalous downward motion together with suppressed convection weakens the O3 outflow of net transport, causing tropospheric O3 to increase over WP. Over CP and EP, the decrease of O3 primarily results from the change of net O3 chemistry by lightning in middle and lower troposphere. In ENM, the intensity of transport and chemistry fluxes is weaker than that in CEN. But the enhanced net O3 outflow can reasonably explain the decrease of O3 over relatively wide region in middle and upper troposphere. In La Nina events, not only the O3 anomalies, but the fluxes of transport and convection are completely opposite to that in ENM.