Study Of Relationship Between Atmospheric Visibility Variation And Ambient Particulate In Shijiazhuang

The atmospheric suspended particles have an impact on the ray radiation and make atmospheric visibility degradation. The suspended particles do much harm to the visual air quality, the urban landscape and the human health. Shijiazhuang city is located in the urban cluster of Huabei Plain which is covered by "atmospheric brown cloud". Environment pollution is worse and the urban haze phenomenon is serious in Shijiazhuang. Shijiazhuang city is a representative city of low visibility in the northern region. However, the special study of atmospheric visibility is relatively weak in Shijiazhuang city. Carrying out the study of the relationship between atmospheric visibility variation and atmospheric particles will be helpful to the research of the cause of regional haze or low visibility in the Huabei Plain and can provide the reference to improving atmospheric visibility.Based on conventional meteorologic and monitor data, the author analyzed atmospheric visibility and its effect factors by SPSS11.5.The results show that atmospheric visibility has been decreasing in recent years in Shijiazhuang city. The yearly average visibility range reduces from 12.7km in 2004 to 10.2km in 2006. The daily average visibility range is between 10～13km. The visibility has obvious spatio-temporal variation. As to the temporal distribution, the visibility is the highest at 14:00 and the lowest at 08:00 during a day; and the best in spring and the worst in summer or winter during a year. As to the spatial distribution, the visibility is lower in the northwest or southwest and higher in the eastern part, and specially the cities of Zhengding and Luancheng are the highest. The impaction factors of atmospheric visibility are analyzed. Among all the meteorological factors, relative humidity is the main influencing factor to visibility range. Among the air quality factors, PM₁₀ is the main influencing factor.The atmospheric visibility has been divided into three ranks firstly based on the observed results from digital imaging in Shijiazhuang city. The visibility is the best under the first visibility rank and the wost under the third visibility rank. By gathering atmospheric particles sample under different visibility ranks, analyzing the characteristics of sample mass concentration, total carbon mass concentration or particle size and shape under different visibility ranks, and exploring the inter relationship among visibility, sample mass concentration, total carbon mass concentration or particle size and shape, the author makes the following conclusion: (1) Under the third visibility rank in Shijiazhuang city, the PM₁₀ mass concentration and total carbon mass concentration average value are respectively 0.486 mg/m3 and 83.0μg /m3, and the average mean size of atmospheric suspended particles is 5.9μm. If the visibility rank rises from the third-level to the second-level and the first-level, the corresponding atmospheric particles average value of PM₁₀ mass concentration was reduced by 54% and 67% respectively, the average value of total carbon mass concentration was reduced by 49% and 61% respectively, the average mean value of atmospheric suspended particles was increased by 59% and 76% separately. (2) The total carbon mass concentration is between 5.43%～61.61% of the PM₁₀ mass concentration. The seasonal average value of the total carbon mass concentration of the PM₁₀ mass concentration accounts for 21% in summer and winter, next is in autumn; which only accounts for 14% in spring. The relevance of total carbon and PM₁₀ is most obvious in fall and winter, and the correlation coefficient r is 0.961.(3) The correlation coefficient r of visibility and PM₁₀ mass concentration is - 0.602, and the r value of visibility and total carbon mass concentration is - 0.652; The relevance is most obvious between the visibility and the particles number percentage of 2～4μm or >10μm in winter, and the r value respectively is - 0.709 and 0.636; The visibility and particle shape is basically irrelevant. (4)The inter relationship among visibility, meteorological factors and air quality factors has been discussed by means of multiple regression. The results show that meteorological factors and air quality factors affect visibility much more in spring and winter, and the duplicate correlation coefficient is above 0.87. The coefficient of multiple regression equation indicates the contribution value of PM₁₀ mass concentration is the biggest in summer, and the contribution value of total carbon mass concentration is the biggest in spring and autumn, followed by relative humidity. The contribution value of total carbon mass concentration is biggest in winter, and next is PM₁₀ mass concentration and relative humidity.On the basis of this study, the measures that can help improve the atmospheric visibility of Shijiazhuang are as follows: improving visibility in winter, the north-western and south-west of Shijiazhuang as a key;controlling the daily average quantity of PM₁₀ mass concentration;greatly reducing the emissions of the total carbon.