| Based on the black carbon?BC?concentration observation data of Zhengzhou in recent12a?2006-2017?,combined with hourly surface temperature,relative humidity,wind direction and wind speed data from Zhengzhou Station from January 2006 to December 2011,the daily variation and basic periodic signals of the BC concentration and surface meteorological elements in four seasons were revealed.At the same time,the connection of the BC concentration and the above meteorological elements were discussed.Using the sounding data from Zhengzhou Station from January 2006 to December 2015 twice a day?08:00 and 20:00,Beijing time,after the same?,the total cloud cover data 4 times a day?02:00,08:00,14:00 and20:00?during the same period,FNL reanalysis data 4 times a day?02:00,08:00,14:00 and20:00?,with a horizontal resolution of 1°×1°,provided by NCEP during the same period,the relationships between the BC concentration and meteorological elements in the lower troposphere were revealed in the clear and non-clear skies,separately.Further more,the objective T-mode principal component analysis method?T-PCA?was used to identify the main polluted synoptic patterns of wintertime BC concentration in Zhengzhou.Finally,the extremely high BC concentration events?December 24-25,2006,January 18-19,2010?and extremely low events?January 23-24,2009,February 17-18,2010?during the study period were filtered out to research the characteristics of the corresponding atmospheric circulation background field,compare the differences,and verify the previous conclusions.The results are as follows.The annual average of BC concentration in Zhengzhou was?8.71±2.42??g.m-3.and the concentration in autumn and winter was obviously higher than that in spring and summer.The diurnal variations of BC concentration in autumn and winter showed a clear double-peak characteristic,and appeared an obvious single-peak characteristic in spring and summer.The diurnal variations of the surface meteorological elements were all single-peak,and the high BC concentration moments corresponded to low surface temperature,high surface relative humidity and low surface wind speed.Harmonic analysis found that the daily variations of BC concentration in Zhengzhou in autumn and winter had a period of 24h+12h,and those in spring and summer had a significant 24h cycle.In the recent 12a?2006-2017?,the wintertime BC concentration in Zhengzhou performed a manifest downward trend.The BC concentration in Zhengzhou in winter showed a significant positive correlation with the temperature,relative humidity and stability of the atmosphere in the lower troposphere.The above relationships were more pronounced in the clear sky.On the 850 h Pa,the high BC concentration appeared in the westerly and easterly wind directions in the clear sky,and there was not much difference in BC concentrations in the wind directions in the non-clear sky.The BC concentration had a reverse relationship with the lower troposphere wind speed.After synoptic classification in the T-PCA method,it was found that synoptic patterns associated with weak southwesterly and easterly winds corresponded to high BC concentration,and those associated with strong northwesterly wind corresponded to low BC concentration.By comparing the 850 h Pa anomalies of two high BC concentration processes and two low BC concentration processes,it could be seen that the high BC concentration corresponded to the obvious warming and humidification of the lower troposphere and weak southwesterly or easterly wind anomalies;the low BC concentration was related to obviously cooler and drier troposphere and strong northerly wind anomalies.The above conclusions are conducive to timely and accurate prediction and treatment of local heavy pollution incidents. |
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