| With the deepening of urbanization in Suzhou, the rapid growth of pollutant emissions, particulate pollution is serious particularly and has a severe impact to the health of the residents. It is important to study the spatio-temporal distribution of particulate matter pollution in Suzhou area, analyze the temporal and spatial variation of haze occurrence, ascertain the cause of meteorological conditions and all of these works can provide an important scientific basis for the accutate simulation of heavily polluted weather and the controlling of the air pollution in the region. In this paper, the pollution characteristics of particulate contaminants in Suzhou area from 2013 to 2015 were analyzed. The water-soluble inorganic ion source was analyzed for PM2.5 in 2012, and the typical cases were selected for WRF-Chem numerical simulations. The main conclusions were showed as follows:(1) The annual average concentrations of PM2.5 and PM10 in Suzhou urban areas were 56.71?g/m3 and 81.64?g/m3 in 2015, which were lower than that in 2013 and 2014 respectively. The average annual PM2.5 and PM10 concentrations in the three years were decreasing yeae by year. The seasonal concentrations of PM2.5 and PM10 were significantly different. The change trends of PM2.5 and PM10 is similar, and they were bimodal for all six stations os Suzhou region. The concentration of PM2.5 and PM10 in winter and spring was high, and the concentration in summer was low. The lowest values of PM2.5 and PM10 occurred in August. The diurnal variability of PM2.5 and PM10 concentration were bimodal with the peak concentraions at 09 am and 19 pm.The average concentration of NO2 was bimodal and it was the highest in winter and the lowest in summer. The SO2 annual average and diurnal average concentration of six cities was not exceeded the limited standards and the variabilitys of SO2 monthly average concentration in the different cities had certain differences. The diurnal average concentration of CO in six cities were not exceeded the national limited standard, the difference between cities was large.(2)During 2012, the average concentration of water-soluble ions in PM2.5 in Suzhou was: SO42->NO3>NH4+>Na+>Cl->K+>Ca2+>Mg2+>F-.SO42-,NH4+,NO3-were the most important three water-soluble ion species, their accumulated concentration in PM2.5 accounted for 50.9% of the total PM2.5 mass concentration. The seasonal characteristics of all the ions were the highest in winter and lowest in summer. The main sources of water-soluble ions in Suzhou PM2.5 were analyzed by principal component analysis. The results were showed that the source was mainly composed of secondary pollution sources and biomass combustion, road dust and industrial emissions, sea salt pollution. Their contribution rates were 32.84%, 19.99% and 18.43% respectively. The wind direction, wind speed and temperature have a significant correlation with the concentration of water-soluble ions, which were the main influencing factors of the local concentration of particulate matter. Due to the influence of monsoon climate, the input paths of the external pollutants in Suzhou City has obvious seasonal variation characteristics,in which the main transport routes in the summer half year were from the seas and the main paths in the winter were from the inland.(3) Using WRF-Chem model to simulate a heavy pollution process in Suzhou region, it was found that there was a high correlation between the simulated values and the observed values of PM2.5, CO, SO2 and the correspondence of their diurnal changing processes were good. The analysis of the weather backgrounds during this polluting process indicated that the high-level atmospheric circulation in the process was relatively straight, a uniformly weak and high pressure system controlled the middle layer and the ground was controlled by a weak high-pressure ridge. This weather situation was easy for the accumulation of polluted particles. In addition,the ground pressure line was intensive and the wind speed was strong and it was conducive to the transportation of pollutants. The investigation of meteorological elements change in the process displayed that this pollution process was mainly affected from the movement southward of haze weather on the large scale from the north China. The north pollution air mass was gradually pushed southward.The local diffusion condition was poor during the period from 14th to 15th, December in 2015,the local pollutants were accumulated and the all of these above factors led to the aggravation of pollution. |
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