1.Institute of Atmospheric Physics, Chinese Academy of Sciences;2.Institute of Urban Meteorology,China Meteorological Administration;3.China National Environmental Monitoring Center
Using WRF and IAP-AACM developed by Institute of Atmospheric Physic, Chinese Academy of Sciences, several typical pollution episodes of fine particulate matter (PM2.5) over Hohhot-Baotou-Ordos area of Inner Mongolia in winter of 2016 were analyzed. The resultes indicated that the air quality changes in Hohhot-Baotou-Ordos area were mainly affected by the large-scale synoptic pattern. In the stage of pollution accumulation, at 500 hPa, this area was controlled by the flat westerly airflow in front of the blocking high pressure or weak high pressure ridge; at the ground, this area was located in the weak high pressure or uniform pressure field. The low wind speed and the low height of boundary layer were unfavaorable for the dispersion of pollutants, meanwhile, the air temperature and relative humidity were high, which was conductive to the formation of secondary particles. In the stage of pollution dissipation, the synoptic patterns had significantly changed. Below the 550 hPa, there was strong cold advection, causing the gale weather on the ground, which were beneficial for the elimination of pollutants. Accompanied by cold air moving southward, pollutants over downstream areas were also removed. Local emission was the main source of PM2.5 over Hohhot-Baotou-Ordos area. The contribution of local emission to Ordos was more than 60%, and Hohhot more than 80%, Baotou more than 90%. The change of air quality in this region could reflect the change of regional air pollution meteorological conditions. Cross correlation analysis showed that the PM2.5 concentrations in Shanxi, Hebei and Henan regions were correlated with that in Hohhot-Baotou-Ordos (P < 0.0001) with a phase difference of 6-24 hours. The improvement of PM2.5 pollution in Hohhot-Baotou-Ordos depended on the control of local source emissions. In winter, the air quality change in this region can be used as a precursor factor for the air quality change in the downstream region, which is helpful for the prediction and early warning of air quality in the downstream region.