Study On Characteristics Of PM_2.5 In Urumqi

Atmospheric particles are the commonest and main air pollutants in China, which have impact not only on human health, but also on visibility, formation of acid rain, cloud formation, and ecosystem. The water-soluble ions, organic carbon(OC), elemental carbon(EC) are important chemical compositions of PM2.5, and closely relating to the condition of air pollutants in the atmosphere. They can reflect the quality of atmospheric environment.Based on online monitoring data of PM2.5 with ambient dust monitor(Grimm 180) at Meteorological Administration(MA) and Meteorological Satellite Station(MSS) in Urumqi, distribution of number and mass concentration data of inhalable particles were analyzed. And the pollution status and sources of water-soluble ions and OC/EC of PM2.5 were discussed. Besides, the influences of meteorological factors on PM2.5 in winter were studied. The main conclusions are as follows:(1) Aerosol number concentration distribution had the same trend at MA and MSS. The maximum values of particle number concentration were between 0.25μm and 0.28μm. Aerosol size distribution showed a bimodal shape with the first peak between 0.30μm and 0.35μm and the second peak between 4.0μm and 5.0μm. Aerosol particles with the diameter less than 2.5μm in the number of particles accounted for 99.88% of the total number concentration. The number of particles within 0.25~0.45μm in winter was the maximum value, while the number of particles larger than 0.45μm in autumn was the maximum value. The number of particles within 0.25~1μm in summer was the minimum value, while the number of particles larger than 1μm in autumn was the minimum value. Diurnal variations of PM2.5 number concentration presented a bimodal shape during heating period and a trimodal shape during non-heating period.(2) The average concentration of PM2.5 at MA and MSS were 61.77μg·m-3 and 43.42μg·m-3, and the excessive rate were 30.81% and 16.44%, respectively. During heating period diurnal variations of PM2.5 mass concentration presented a single peak which appeared in 19:00 to 21:00 at MA, but a bimodal shape at MSS. While during non-heating period diurnal variations of PM2.5 mass concentration presened a bimodal shapes at two sites. The distributions of PM2.5 mass concentrations had little difference between weekdays and weekends. That was because social activities were not significantly different between weekdays and weekends. Besides, the terrain and weather conditions were not conducive to the diffusion of atmospheric pollutants in Urumqi. The seasonal distrubutions of PM2.5 mass concentrations were winter> autumn> spring> summer at two sites.(3) The total water-soluble ions of PM2.5 at Meteorological Administration Tree-ring Laboratory(TRL) and Meteorological Satellite Station(MSS) sites were 88.03μg·m-3 and 65.11μg·m-3, and accounted for 81.99% and 86.24% of PM2.5 mass concentrations, respectively. Seasonal variations of water-soluble ions were: SO42-、NO3-、Cl- and NH4+ showed winter> autumn> spring> summer; Na+ showed winter> autumn> summer > spring; Ca2+ showed autumn> summer> spring> winter. SO42-, NO3- and NH4+ were the major species in water-soluble ions, and they were mainly in the form of(NH4)2SO4、NH4HSO4 and NH4NO3 in PM2.5. Cl- and K+ were mainly from the burning of fossil fuels and emissions of biomass; Ca2+ and Mg2+ were mainly from soil, secondary dust and burning of coal. NO3- and SO42- concentration ratio was 0.40, and it showed that stationary source emissions were still the main pollution in Urumqi.(4) The OC、EC of PM2.5 at TRL were 15.73μg·m-3 and 5.48μg·m-3,and accounted for 9.15% and 3.19% of PM2.5 mass concentrations, respectively. The OC、EC of PM2.5 at MSS sites were 18.23μg·m-3and 6.02μg·m-3,and accounted for 9.26% and 3.06% of PM2.5 mass concentrations, respectively. Monthly variations of OC presented a single peak at TRL, but EC had no significantly difference. Seasonal variations of OC were winter> autumn> summer > spring, and EC were autumn> winter> summer> spring. OC and EC concentration ratio showed the maximum in winter, and SOC concentrations were higher in January and February at two sites; Good correlation was found between OC and EC in spring and summer, indicating that the emission sources were simple relatively in spring and summer; on the contrary, bad correlation was found between OC and EC in autumn and winter.(5) PM2.5 mainly came from the emission of southeast suburb and the carrying of northwest airflow, and the relative humidity and wind speed had great influence on PM2.5 mass concentrations.