| Along with the development of economic society,air pollution problem is more and more severe.Recent years,air pollution incident in Harbin has increasing trend year by year.Temporal & spatial regularity of air pollution days and pollutant concentration is studied in the paper by according to statistics and analysis of air quality observation data in 2006~2015,companied with MICAPS meteorological data etc.The paper also summarizes circulation background and weather situation during the pollution.The quantitative research is performed on the relation of AQI and meteorological factors such as wind,precipitation as well as the relation to fog-haze phenomena and revision layer.The results show: 1)there are 729 air pollution days during the past 10 years in Harbin urban area.The number of the air pollution days is increasing year by year.Especially after 2012,the days sharply increase and heavy air pollution appears frequently.Air pollution days of which 30 percent are heavy air pollution occur every year,about 30% of all days.2)Occurrence of air pollution mainly distributes from October to February in which 84% of the air pollution days presents.Mostly,the air pollution days account for 45% during December to January.Heavy air pollution always occurs in the autumn-winter season in which the days account for 95% of total heavy air pollution days.3)Air pollution more likely occurs in the main urban region than in the suburbs,as well as pollution degree more serious in the urban.4)PM2.5 and PM10 average concentration raise from 2013 to 2015.It means heavy air pollution over Harbin urban area.The primary pollutan is PM2.5.5)Concentration of the four air pollutants show a “double peak and double valley”variation with two highest points at 8:00~10:00 and 20:00~22:00 and two lowest point at 14:00~15:00 and 5:00 in next days.PM2.5,PM10 and NO2 both has characteristics of high value in daytime and low value in nighttime.Due to descending rate of the pollutants higher in daytime than that in nighttime,the night air pollution is totally heavier than the day air pollution.The variation of SO2 concentration is contrary to the PM2.5,PM10 and NO2.6)Characteristics of atmospheric circulation are presented in winter during the high air pollution year.Latitudinal circulation is found from the low troposphere to the middle troposphere.A trough and a ridge are shown in 500 hPa isobaric surface where Heilongjiang province is located behind the trough and before the ridge.The research area is sited in front of a weak ridge or weak continental high pressure with uniform distribution pressure field.The isobar could not be drawn in Harbin and the wind near surface is close to zero.A warm tongue exists in lower atmosphere over Harbin.7)Atmospheric circulation in autumn is obviously different from winter.The research area is located at front of a trough or low pressure center in the lower atmosphere and near surface layer.Southwest wind is strong companied with evident temperature increase.The air pollution over Harbin is related to the straw burning.8)The synoptic situations of air pollution in Harbin are categorized into five categories: rear of low-pressure,low-west and east-high trough,south-high,uniform pressure and the center of high pressure.The five synoptic situations except low-pressure have something in common.At the early stage,the middle layer of the troposphere maintains the zonal circulation,and the temperature of the lower layer is obviously warmed up and the wind power is increased.The temperature rising range reached 4~8 ℃,and the winds usually increase to 8 m/s or more.On the surface wind field,the winds of low-west and east-high trough,south-high are southwest and east,respectively.The others are in the weak pressure field with weak wind.When the radial circulation of 500 hPa is increased and the middle and low level have cold air intrusion,the wind of ground turns to north and the urban air pollution relieved or ended.However,the intrusion process of cold air is usually corresponded to the moments of the most polluted situation.9)AQI is negatively correlated with the annual average wind speed with the correlation coefficient of-0.254.The correlation coefficient is notably-0.6 in winter,and the correlations of other seasons are not obvious.The PM2.5 and PM10 mass concentrations are negatively correlated with mean wind speed in winter,and the correlation coefficients are-0.616 and-0.511,respectively.The correlation between PM2.5 mass concentration and average wind speed is not significant,but PM10 mass concentration is positively correlated with mean wind speed,with the correlation coefficient of 0.143.When the wind speed is below 3m/s,the correlations between AQI,pollutant concentrations and wind speed are significant negative.Nevertheless,when the wind speed exceeds 3m/s or more,the wind has dual effects on air quality.10)The height of thermal inversion layer is significantly positively correlated to AQI in autumn and winter with the correlation coefficients of-0.13 at 08:00 and-0.118 at20:00,respectively.The correlation coefficients between the thickness of thermal inversion layer and AQI are 0.124 at 08:00 and 0.113 at 20:00,respectively.The strength of thermal inversion layer has insignificant effect on AQI.When the AQI is over 200,the correlation between the parameters of thermal inversion and AQI are not obvious.11)The precipitation of more than 5mm has obvious purifying effect on the air during the autumn and winter.The probability is 78% if AQI was below 100 and the probability is 0 if AQI higher than 200.AQI is higher than 150 with the probability of 39% or higher than 200 with the probability of 20% when precipitation is below 0.1mm.The weak precipitation could not improve the air quality,on the contrary accompanying with increased air pollution.12)The proportions of haze days increase when the air pollution increased,when AQI is more than 200,56 days of 137 days are haze days,accounting for about 41%.For AQI more than 300,the haze days account for 60%.In addition,the haze day of AQI higher than 200 account for 77.8%of all day haze day.Different from the haze,80% of the fog is accompanied by pollution weather.When haze mixed with fog,the most serious air pollution occurrs with AQI more than 500. |
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