Effect Of PM_2.5 Variation Characteristics For Meteorological Factors In BeiJing Winter

Fine particulate(often referred to as PM_2.5) is an important part of particle pollution. It is small in diameter（d<2.5 micrometers）, always less than 1/20 width of of a single human hair and can only be seen with an electron microscope. Compared with the other particles, such as PM10, the larger size of particles, the PM_2.5 are closely linked to atmospheric visibility, air quality and human health. The dangers of fine particulate matter are bigger than the other particulates, because of the long retention time in the air and small diameter, some research suggests that PM_2.5 tend to penetrate into the gas exchange regions of the lung（alveolus）, and may pass through the lungs to affect other organs, so that the concentration of PM_2.5 in air are more close to human body health. Previous studies have suggest the diffusion velocity and accumulation rate of PM_2.5 was been affected by the conditions of meteorological and the characteristic of underlying surface. So the study of human respiratory high PM_2.5mass concentration for the response of the meteorological elements, vegetation form of underlying surface（forest and lawn） has an essential significance.In this paper, depending on the date from Beijing Municipal Environmental Monitoring Center and observation, we analyzed the relationship of PM_2.5 mass concentration with humidity, temperature, wind speed and the direction of the wind in height of human respiratory, by using the methods of correlation analysis, regression analysis, path analysis, statistical analysis, Kriging interpolation analysis.The main research results and conclusion showed that:1、Various characteristics of air quality during winter（2014²015） in BeiJing.（1）The month of PM_2.5 mass concentration and air quality index（AQI） from bottom to high was December, February, January; the sequence of PM_2.5 concentrations and AQI in four types of function monitoring stations from low to high is traffic monitoring point, control point, urban environment point and suburban environmentpoint. The pollution level of BeiJing in winter is mild or moderate.（ 2） The characteristics of AQI and PM_2.5 concentrations are presented that diminishing from south to north, and the north-south difference is obvious, through analyzing of the Kriging maps.（3） SO2, NO2 and O3, CO and PM_2.5 show significant correlation, in four kinds of stations. It was significant positive correlation among SO2, NO2, CO and PM_2.5,but it was opposite with O3, obviously.2、Under different weather conditions, the relationship of PM_2.5 concentrations with meteorological factors as follows:（1） PM_2.5 mass concentration is characteristic of high in morning and evening and low at noon in smoggy days; Short term snow can exacerbate air pollution at night. PM_2.5 mass concentration maintain to low-concentration in wind day, the air quality keep in excellent and good.sunny day,the air quality keep in excellent and good from 0:00 to 16:00, after 16:00 particle concentration gradually rising trend.（2）It was significant positive correlation between wind speed and temperature, but it was opposite with humidity; temperature was negatively correlated with humidity; PM_2.5 mass concentration with temperature, wind speed show negative correlation, when the PM_2.5 mass concentration maintain high level, which correlation is good.3 、 In different pollution level :（1）Mild to moderate pollution days, if the temperature is low, the average daily wind speed equal 0.76 m/s, humidity is big, the moisture is the decisive factor in the change of PM_2.5mass concentration; then temperature, humidity, wind speed were all high, the three combined effect of PM_2.5mass concentration variation; When the wind speed, humidity, temperature are all small, the three comprehensive effect PM_2.5 mass concentration of changes. This suggest that changes in the height of the human respiration PM_2.5 mass concentrations of meteorological factors are extremely sensitive;（2）In a Heavy Pollution process,PM_2.5 mass concentration is cause mainly the humidity, while the temperature effect by humidity,in addition during the daytime northwest wind, northeast wind larger butthe durationis segment,the night southeast, southwest wind speed is small but long duration, conducive to pollutant accumulation;（3）Short of tiny amount of snow can’t lower the quality of PM_2.5concentrations, due to the decreasing temperature,increasing humidity of the air, makes its concentration increased. And when the hour average wind speed reach 3.9 m/s, the fine particulate matter in the air are quickly diffused.4 、 Under different underlying surface.（1）In the accumulation of PM_2.5concentrations, the shrubland average daily levels of PM_2.5 always less than the lawn indicated that the PM_2.5 was diluted by woodland better than lawn.（2）From the diurnal Variation Characteristics of PM_2.5 concentrations, the PM_2.5 concentrations was diluted by shrubland at night, it was diluted depending on meteorological factors in daytime.