| Based on the tropospheric ozone (TO) and related trace gases data from HongKong and low latitudes area of Pacific regions, this study mainly analyze the long-term characteristics of tropospheric ozone over south coastal China and its relationship with the annual cycle of atmosphere circulation with several methods and models, such as Kolmogorov-Zurbenko (KZ) filter, Lagrangian dispersion modeling of carbon monoxide, calculation of an monsoon index, Nino 3.4 index and GEOS-Chem simulation and so on.In this study, the data of surface ozone and carbon monoxide (CO) obtained from 1994 to 2010 at a coastal site in Hong Kong, are analyzed and their temporal variation and trend as well as their possible causes are discussed. The histogram distributions of ozone show two peaks around 18ppbv and 40ppbv, but the frequencies of high concentration ozone occur more in recent years. The ozone concentration increased by an average rate of 0.52ppbv/yr, with a larger increase in autumn (0.654ppbv/yr). The KZ filter was used to separate different scales of motion in ozone time series. It is shown that seasonal variations, mesoscale weather system and daily meteorology plays more important role than other time scales in changes of surface ozone concentration. The trend of the interannual variations of ozone increased by an average rate of 0.65ppbv/yr.By analyzing 11 years of ozonesonde data over HongKong, this study discussed the impact of the East Asian monsoon (EAM) on climatology and interannual variability of tropospheric ozone over the coastal South China. The seasonal cycle of ozone in the lower troposphere is highly related to the EAM. The transports of pollutants from continental anthropogenic and biomass burning origins induced by the EAM caused ozone enhancements in the free troposphere. Lower TO levels showed high interannual variability, the annual averaged amplitude up to 61% and 49% in the boundary layer below 3 km altitude. In spring and autumn, the interannual variability of TO in boundary layer was predominately influenced by the EAM intensity, with high ozone levels associated with northeasterly circulation anomalies.The inter-annual variation of tropospheric ozone somehow related with ENSO signals. Ozone peaks in the winter-spring associated with El Nino explosion, but valleys generally occurred in the summer-autumn associated with the ending of El Nino events or explosion of La Nina. The deseasonalized ozone shows positive trend during La Nina events but negative one during El Nino. For the year of ozone peaks (valleys), subtropical high moves north (south)wards, the anticyclone (cyclone) anomaly located in the center of south China and cyclone (anticyclone) anomaly located in west-north Pacific. The circulation induced more (less) polluted airmasses from Eastern China. Meanwhile the convection activities is weak (strong) and the downward shortwave radiation is strong (weak), these could cause high (low) levels of ozone in annual scale.During El nino events the zonal circulation prevailing in the mid-high latitudes, positive ozone anomalies exist in mid-high latitudes area of Asia and North America, negative anomalies exist in South China. There are two polluted airmass transport bond alone from the north Japan to Maunna Loa (ML) and from South China Sea to ML and along lead to high ozone levels in ML. During La Nina events the meridional circulation prevailing in the mid-high latitudes, negative ozone anomalies exist in mid-high latitudes area of Asia and North America, pozitive anomalies exist in South China. The ozone levels in ML is lower, because there are less polluted airmass from Asian to Pacific area. When discuss about the real effect of anthropogenic emissions to ozone pollution, it is important to consider the inter-annual/decadal variation of atmosphere circulations associated with the monsoon and ENSO. |
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