| Beijing-Tianjin-Hebei(BTH)region is important political,economic and cultural center in China.With great development of regional economic in recent years,regional air pollution caused by rapid urbanization and industrialization becomes one of the problems which affect people's life quality and restrict the development of the region.Firstly the spatial and temporal characteristics of air pollution were analyzed over BTH region from 2013 to 2016.And the relationship pollutant mass concentration and meteorological factors were also analyzed.Secondly,circulation weather types were identified over BTH region by using objective classification methods.The characteristics of pollutant concentration asscociated with key meteorological parameters under different types were analyzed.WRF Chem model was used to analyze pollutant characteristics,meteorological condition and effect of terrain during heavy pollution episode.Finally,based on step-wise regression method statistical pollutant concentration forecast models were built over BTH region.An air pollution forecast system was built aided with computer technology.The main results were as follows:(1)Annual average air quality index(AQI)decreased from south to north in BTH region for the past few years.The high value center was located in central and southern Hebei province,AQI was low in the northern Hebei with rare heavy pollution episodes.Primary pollutant were mainly particulate matters including PM2.5 and PM10 in BTH region.Its occurred frequently that O3 was primary pollutant in several cities such as Chengde and Zhangjiakou.(2)Pollutant concentration decreased year by year in Beijing,Tianjin and Shijiazhuang with small variation for CO,NO2 and O3 concentration.In general,pollutant concentration was high in winter and low in summer except for O3.Due to straw burning PM2.5 concentration was slightly higher in June and July.Every pollutant had obvious diurnal variation.O3 concentration were highest from 14:00 to 16:00 and lowest during night.Concentration of the other five pollutants was highest in the morning or at night and lowest at about 16:00 in the afternoon.(3)Correlation analysis showed that pollutant concentration had a close relationship with surface meteorological factors and boundary layer parameters.PM2.5 and PM10 concentration had significant positive correlations with relative humidity and stable energy while they had significant negative correlations with wind speed and maximum maxing depths(MMD).O3 concentration had a positive correlation with temperature.In winter,O3 concentration had negative correlations with wind speed and stable energy and positive correlation with MMD.(4)Nine circulation weather types were identified over BTH region during winter from 2013 to 2016 and they were classified into five groups.Air pollution of types with high pressure to the front of the BTH region was lighter,while air pollution of types with high pressure fields and the rear of high pressure was heavier with weak wind,high relative humidity,high stable energy and low MMD which reduced the possibility of dilution of pollutants from the local area,therefore,the observed averaged AQI values were almost above 150 in every city.Two heavy air pollution episodes in February 2014 caused by the persistent high pressure fields which lasted for a few days.The evolution of the high pressure system led to strengthening of the northerly wind,which reduced the concentration of pollution over north cities of the BTH,however,southerly winds carried air pollutants to make the concentration increase rapidly in the north cities of the BTH.(5)WRF Chem model was used to simulate a heavy air pollution episode which occurred from November 26 th to December 2nd over BTH region.Surface weather situation changed from high pressure field to the rear of high pressure with weak wind,high relative humidity and low PBLH which reduced the possibility of dilution of pollutants from the local area.High PM2.5 concentration existed in the inversion layer associated with weak wind and high relative humidity in boundary layer.Sensitivity test showed that terrain played an important role during air pollution episodes.Pollutants gathered together in the east of Taihang mountain and south of Yan mountain due to terrain.If terrain heights were reduce,pollutant would cross over the mountain and move to northwest,which would make PM2.5 concentration increase in northwest Hebei.(6)Based on step-wise regression method statistical models for pollutant concentration forecast were built over BTH region.An air pollution forecast system was built aided with computer technology.Verification results showed that model simulated results were in accordance with actual results for pollutant concentration and AQI.The air pollution forecast system had abilities to automatically calculate and display meteorological parameters and air quality forecast over BTH region which provided help for forecasters. |
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