Tempeoral And Spatial Distribution Of Haze In China And Its Association With Climate Change

The purpose of this paper is to investigate the temporal and spatial distribution characteristics of hazes through analyzing observation data available from major 721 meteorological stations across China for the period of 1961 to 2007.The study focuses on the mechanism of how climate factors such as wind,precipitation and monsoon circumfluence impact on the haze.The paper statistically analyzes the effect of haze to atmospheric visibility,solar radiation,sunshine time,atmospheric optical thickness and urban heat island.(1) Preliminary results indicate that hazes occur mainly in eastern China,east of 100(?)E,and southern China,south of 42(?)N,with some significant high-incidence centers called "muddy island".The nation as a whole average haze day per year is 5.65.Areas with more than 10 days per year are the middle and west part in northern China,southeast portion in Northwestern China,most areas in central China and eastern China,the west part in western China and southern China.(2) Hazes occur more frequently during winter than during summer.(3) The nation as a whole average haze day per year is only 2.4 in 1960s while more than quadrupled in 2000s.This is a statistic,ally significant increase.(4) During a period of 47 years,hazes in China nationwide have increased with a linear tendency of 3.19 days per decade and two abrupt change points,respectively in the mid 1970s and after the year of 2000.From 1961 to 1975,hazes in China occur less than the average with negative phase.Hazes fluctuate in weak positive phase from 1976 to 2000.In recent 5 years,hazes drastically increase every year.(5) Interannual variabilities of haze days in detail stations can be roughly classified into three categories.The first category is undulately rising, such as stations located in the eastern and southern China.The second category is a haze days peak in 1970s-1980s and decreased recently such as stations located in northern China and near western China.The third category is interannual oscillation frequently such as stations located in southwestern China. (6) The correlation coefficients,interannual scale,between hazes and three wind force indices(i.e.the number of days with wind force f≥5m/s,f≥10 m/s and f＜3 m/s) are -0.809,-0.734 and 0.788 respectively.These significant correlations explain that the change of wind's dilute ability for air pollution does exert obvious influence on tendency of hazes.(7) Most of the correlation coefficients between hazes and wind force f≥5 m/s is negative to the north of 35°N while positive to the south of 35°N.The distribution of correlation coefficients demonstrate that one kind of sources of the haze in northern China are flying dust,flying sand and sandstorms which often happens in the Northwestern China.Strong wind is favorable for the floating dusts carrying.(8) The precipitation impose an obvious effect on the increasing trend of haze day.The correlation coefficients between haze day number and the number of day precipitation 0.1-0.9mm reaches -0.716.It indicates that light rain can also significantly reduce the appearance of haze.(9) In recent 5 years,2002-2007,hazes drastically increase each year. According to comprehensive analysis of the variation of precipitation and wind forces,two main reasons are found that the day of wind force f≥5 m/s decreased and the precipitation reduced in the 5 years.(10) Comprehensive analysis of the Shi Neng monsoon index I_SHI and Zu Yanfeng monsoon index I_EAWM,the study finds less haze days in strong monsoon year and more haze days in weak monsoon year.Significantly correlation is found between the decadal variation of I_SHI,I_EAWM and haze day,the correlation coefficients is -0.420 and -0.387 respectively which reach a =0.01 significance testing standard.(11) The visibility in atmosphere deceased steadily in the 47 years.The percentage of the number of haze day in bad visibility day(visibility 1km-10km) increased.It was 11.9%in 1961 while 51.7%in 2007,having multiplied 4.3 times.There were significantly correlation between hazes and good visibility,bad visibility,the correlation coefficients are -0.783, 0.785 respectively.(12) Haze result in going down of surface solar radiation and the decreasing of sunshine time.The average surface solar total radiation in 1997-2007 were lower 10.1%than 1960s';The average sunshine time in 1997-2007 decrease 213 hours than 1960s',about 10.1%.(13) Atmospheric optical thickness in main area of haze is one fourth higher than it not in main area.The results suggest haze has obvious effect on atmospheric optical thickness.Computing the correlation coefficients between the number of haze days and atmospheric optical thickness reaches 0.773,far beyond a =0.001 significance testing standard.It shows that haze thickening the atmospheric optical thickness directly.(14) With the increasing of the num of haze day,the urban heat island is higher than before.Among 12 city's correlation coefficients between haze and urban heat island,most of them are positive correlation.For example,the correlation coefficients of Shanghai is 0.676,far beyond a =0.001 significance testing standard.