| As an important component of the atmosphere, aerosol has a significant impact on human life, regional radiation balance and climate change. Retrieval of the ground atmospheric particulate matter mass concentration （of PM2.5/PM10） from satellite aerosol optical depth （AOD） product is becoming a hot topic of research and development direction in recent years. However, the studies found that correlation between AOD and PM2.5/PM10and corresponding dependent equations has significant difference for different regions at different times, which will inevitably lead to a big error in concentration of particulate matter retrieved from satellite product.In this paper, temporal and spatial variatioin characteristics of atmospheric particulate mass concentration and aerosol optical properties in Beijing-Tianjing-Hebei background regions, Beiijng city and its suburbs is analyzed. Based on this, correlation between regional AOD and concentration of PM2.5/PM10and its space-time difference is also discussed, which may provide scientific basis for research and development of model to retrieve PM2.5/PM10concentration from AOD in Beijing-Tianjing-Hebei region. The main results show that:（1） Pollution of ground particulate matter （of PM2.5/PM10） in Beijing-Tianjin-Hebei region is serious. The annual mean concentration of PM2.5in regional context, Beijing and suburbs were36±5μg·m-3,65±145μg·m-3,80±20μg·m-3 respectively. All of them are beyond the control standard concentration proposed in2016, in which PM2.5annual average concentration is35μg·m-3 while daily average concentration is75μg-m-3, and the mean excessive rate were9%,35%,43％respectively. Moreover, the fine particle pollution presents significant regional characteristics with a significant linear correlation between PM2.5daily average concentration of the three stations. PM10annual average concentration in Beijing urban district and suburbs were117±3μg·m-3 and146±33μg·m-3, respectively. The values were beyond the current national PM10annual control standard (1003μg·m-3) and over-stand rate were26%and39%. Fine particle PM2.5pollution and coarse particles PM10pollution exihibited highly significant correlation and the correlation coefficient is about0.90（p<0.001）. The proportion of PM2.5in PM10gradually increases from spring to winter with higher value in urban region than in suburb region and the proportion were61%and56%, respectively. （2） Aerosol optical depth （AOD） and aerosol modes （of Angstrom exponent,:a） has obvious seasonal variation in Beijing-Tianjin-Hebei region and there are some differences of aerosol optical properties variation for different regions. AOD in Xinglong Regional background Station showed higher value in summer and autumn while lower value in winter and spring with variation ranging from0.25to0.41. Beijing urban AOD was highest in spring and lowest in winter and season range was from0.49to0.62. In xianghe suburbs region, seasonal mean value of AOD was highest in summer and lowest in autumn with seasonal range from0.58to0.65. Seasonal variation of modes in three typical region represented similar characteristics with higher a-value in summer and lower a-value in winter. Seasonal variation ranges of a-value in these three stations were0.56to1.04,1.02to1.19,1.03to1.15, respectively. Air quality in Xinglong background Station, less impacted by human activities, was better than air quality in urban and suburban regions. At this station, where coarse particles accounted for the master modes, annual average AOD and a was relatively lower, with values0.34±0.07,0.81±0.24, respectively. In Beijing regions, annual average AOD and a was higher with values0.55±0.10and1.12±0.08. In Xianghe region, AOD and a annual average was0.62±0.10,1.09±0.11, repectively. Aerosol wavelength exponent a changed exponentially with AOD at Xinglong Station. Aerosol wavelength exponent a in urban and suburban regions, with values between0.8and1.6throughout the year, did not changed significantly with AOD. Moreover, the master modes was relatively stable in these regions. These results indicated that aerosols in Beijing urban and suburban regions was seriously impacted by anthropogenic aerosol emissions （mobile emission）.（3） Correlation analysis showed there was a significant linear correlation （y=ax+b） between AOD （x） and PM2.5/PM10（y） at three typical stations with differenct correlation coefficient and dependent equations in different seasons and regions. As a result, annual correlation may mask seasonal variation and large difference of correlation. The annual correlation equation was y=60.83×+15.45（R=0.69） for Xinglong Station. But there existed a range of42.66～69.53for a,9.48～26.62for b,9.48～26.62for R in different seasons and correlation was more significant in spring and autumn than in summer and winter. The annual correlation equation was y=56.19x+23.16（R=0.68） for Beijing city station. But there existed a range of45.54～89.70for a,16.89-25.89for b,0.69～0.89for R in different seasons and the correlation was significantly higher in summer and autumn than in spring and winter. The annual correlation equation was y=55.01x+43.51（R=0.51） for the Xianghe Suburban station. But there existed a range of41.41～98.91for a,37.97～47.17for b,0.53～0.62for R in different seasons and the correlation in summer and autumn was significantly higher than in spring and winter. These results indicated that there is a high linear correlation between AOD and PM2.5in the Beijing-Tianjin-Hebei region. However, due to the spatial and temporal differences in aerosol composition and meteorological elements, there were large regional and seasonal systematic difference for correlation between AOD and PM2.5. As a result, a single linear correlation equation can not have a precise spatial and temporal representation, and will introduce a large systematic bias when it is applied in different seasons and different regions.（4） The annual correlation equation for AOD （x） and PM10（y） at the urban station was y=81.01×+58.36（R=0.60）, where b ranged from40.49to73.04with variation of season while R ranged from0.50to0.73, and correlation was significantly higher in summer and autumn than in spring and winter. The annual correlation equation for AOD （x） and PM10（y） at Xianghe Suburban station was89.28×+90.79（R=0.50）,where seasonal variation for a was49.81～165.22while seasonal variation for R was0.48～0.62, and correlation was significantly higher in summer and autumn than in spring and winter. Results also showed that the correlation between AOD and PM10was lower than the one between AOD and PM2.5. In addition, correlation coefficient and equation for AOD and PM10had more significant difference than them for AOD and PM2.5in different seasons and regions. Correlation coefficient between AOD and PM2.5/PM10was improved When humidity correction for PM2.5/PM10data and altitude correction for AOD was performed taking into account of the role of humidity, temperature, boundary layer height and other meteorological conditions. |
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