Analysis On The Pollution Characteristics And The Impact On Visibility Of Atmospheric Particulate Matters During Serious Episode In Winter In Guanzhong Region

Since reforming and opening,with the rapid development of economy,urbanization and industrialization,the air pollution in Guanzhong region continues to grow,especially in winter,which has aroused widespread concern in society.In order to get the characteristics of atmospheric pollution in the Guanzhong region during the winter,two test points were selected in Guanzhong region,one was located in the urban and the other was located in the marginal area.ELPI+,four channel and medium flow sampler were used to collect particles in the atmospheric environment,respectively.Based on the collected data of conventional gaseous pollutants,visibility and meteorological data,the characteristics of particles concentrations,size distribution,diurnal variation and composition in Guanzhong region in winter were analyzed.The main research conclusions were given as follows:?1?During the sampling campaign,the mass concentrations of PM₁₀0 and PM_2.5.5 in the urban and marginal areas in Guanzhong exceeded the China's national ambient air quality standards,and the concentrations of SO₂,NO₂,CO and O₃ were not exceed the standard in two regions.Particulate matter was the primary air pollutant in Guanzhong region in winter.The ratios of PM_2.5/PM₁₀0 in the urban and marginal areas were measured to be 0.22⁰.57 and0.36⁰.90,with an average of 0.42 and 0.71,respectively.This showed that compared with the urban area,the pollution characteristics of fine particles in the fringe area were more significant.The ratios of SO₂/NO₂ in the urban and marginal areas were measured to be0.25⁰.38 and 0.43¹.26,with an average of 0.30 and 0.64,respectively.This indicated that the ambient air quality in the urban area was greatly affected by the moving source during the winter,while the marginal area were affected by the mobile source and the coal-fired heating.?2?The total concentrations of particles in number,surface area and mass in the urban area were 2.19,1.52 and 1.76 times higher than those in marginal area.The results indicated that total number concentrations was dominated by the particles that size between 0.006 and0.017?m;the particles that size between 0.1 and 1?m were the main contributor to surface area concentrations;the particles that size between 1 and 10?m were the main contributor to mass concentrations.The daily variation of the particles number concentrations of the four modes were all in double-peak pattern in the urban area,while the nucleation mode and Aitken mode were in three-peak pattern in marginal area.?3?Poor ambient air quality in marginal area of Guanzhong was probably caused by northeast wind,higher relative humidity,lower mixing layer height and atmospheric pressure.From the view of pollutants emission,the average concentrations of PM_2.5,SO₂,NO₂ and CO in serious pollution period were 16.56,3.76,3.05 and 2.90 times higher than those in clean days,respectively,which indicated that fine particles was the dominant pollutant during pollution periods.?4?During the test period,the significant increase of particles that size between 0.1 and1?m was the main reason for the deterioration of ambient air quality.During the severe pollution stage,the number concentrations of particles that size between 0.1 and 1?m was4.85 times higher than those in clean days,and the surface area concentrations and mass concentrations increased by 15.99 and 24.43 times,respectively.And with the deterioration of air quality,the peak particles size continued to migrate to large.?5?The SO₄^2-and NO₃^-were the major pollution components of PM_2.5.The average mass concentrations of SO₄^2-and NO₃^-in serious pollution period were 67.76?g/m³ and 81.26?g/m³,which were 6.72 and 47.24 times higher than those in light pollution period,respectively.From the proportion of the chemical components in PM_2.5,the average proportion of nitrate and sulphate in the severe pollution stage were 26.16%and 24.84%,which were 9.02 and 1.52 times higher than those in mild pollution period,respectively.This indicated that NOx emissions contributed more to the formation of local air pollution.?6?The mass concentrations of particles were exponentially correlated with visibility,but the correlation coefficient were different under different relative humidity.When70%?RH<80%,there was the best correlation between particles concentrations and visibility,the correlation coefficient R² was 0.89.When RH?80%,the correlation between the two gradually weakened.The attenuation degree of particles on atmospheric visibility were different in different size ranges.The particles that size between 0.4 and 1.6?m had significant influence on the visibility,and the correlation were more than 80%;especially the particles that size between 1 and 1.6?m,the correlation reached 97%.