Research On The Atmospheric Particle Size Distributions And The Correlation With The Vairation Of Visibility In Shijiazhuang City

Atmospheric particulate mass concentration is an important indicator of urban air quality,and an important factor to affect atmospheric visibility. When the particles mass concentrationis certain, the environmental effects of atmospheric particles matter depend mainly on the sizedistributions. Environment is worse and the urban haze phenomenon is serious inShijiazhuang. Shijiazhuang city is a representative city of low visibility in the northern region.Carrying out the study of the relationship between atmospheric visibility variation and sizedistribution of particles will be helpful to the research of the cause of regional haze or lowvisibility in North China region and offers scientific basis to control the air pollution andvisibility.Based on conventional meteorological data, the author analyzed atmospheric visibility.In2006, the declining of atmospheric visibility is controlled in Shijiazhuang. Atmosphericvisibility is improved year by year from2007-2009,1km per year. In2009, it’s annualaverage is14.09km, while in2010, it is13.15km. The frequency of visibility of a good gradein recent four years is11.66%, while from2000-2002is25%, which means the atmosphericvisibility in Shijiazhuang is still very low. Based on K-Means Cluster analysis, theatmospheric visibility has been divided into three ranks. The visibility is the best under thefirst visibility rank and the worst under the third visibility rank. Compared with the frequencyof visibility of a good grade from1960-2002above60%and from2000-200240.1%, thefrequency of visibility of a good grade in recent four years11.66%is declined.In Shijiazhuang, Atmospheric particulate mass concentration is mainly fine particles, andthe average of PM_2.1/PM₁₁is57%. The peak of size distribution of particles is≤0.43μm. Butin each particle size segment, the Atmospheric particulate mass concentration decreases.Compared with the size distribution of particles in normal weather, the percentage ofAtmospheric particulate in≤0.43μm increases, while in7¹1μm the percentage decreases,which means that rainfall has great impact on the scavenging of particles. In cloudy weather,and the PM_2.1mass concentration average value is0.48mg/m³, higher than0.25mg/m³, whichWHO set for the daily mass concentration of atmospheric particles.The size distribution of particles is different from season to season. In spring, the mass concentration of atmospheric particles in7¹1μm is higher than any other season. In summerand autumn, the highest mass concentration of atmospheric particles distribution is in0.43⁰.65μm, and in winter the highest is in≤0.43μm.Atmospheric visibility is an important indicator of urban air quality. Under the thirdvisibility rank in Shijiazhuang city, the PM_0.43and PM_0.43⁰.65mass concentration is the keyfactor causing the decline of atmospheric quality.The size distribution of particles under the third visibility rank shows that PM_0.43andPM_0.43⁰.65mass concentration is key factor causing the decline of atmospheric quality.Atmospheric visibility is affected mainly by meteorological factors and atmospheric particlemass concentration. In different seasons, the affection of different factors to extinctioncoefficient is different. In Shijiazhuang, the correlation coefficient of visibility and PM_0.43⁰.65mass concentration is the best. To make the atmospheric visibility above19km, PM_0.43⁰.65mass concentration should be controlled under0.006mg/m³; In spring, the correlationcoefficient of visibility and PM_0.43mass concentration is the best. So in spring, to make theatmospheric visibility above19km, PM_0.43mass concentration should be controlled under0.014mg/m³; In winter, the correlation coefficient of visibility and PM_0.43⁰.65massconcentration is the best. To make the atmospheric visibility above19km, PM_0.43⁰.65massconcentration should be controlled under0.012mg/m³; While the correlation coefficient ofvisibility and the Atmospheric particulate mass concentration in summer and autumn hasn’tbeen tested significantly.This study analyzes the characteristic of size distribution of particles aboutShijiazhuang,largely about Atmospheric fine particles.The size distribution of particles isdifferent from season to season, in spring the mass concentration percentage of PM7¹1ishigher than other seasons. In summer and autumn the mass concentration profile showedpeaks at PM_0.43⁰.65, while in winter is at PM_0.43.In Shijiazhuang, the correlation coefficient ofvisibility and PM_0.43⁰.65mass concentration is the best. To make the atmospheric visibilityabove19km, PM_0.43⁰.65mass concentration should be controlled under0.006mg/m³.