Pollution Characteristics And Formation Causes Of Atmospheric Particles And Its Chemical Components In Lanzhou City

With the rapid development of urbanization and economic growth, atmospheric pollution in urban areas has been serious in China. The main atmospheric pollutant in most of the cities is inhalable particle (PM10). Atmospheric particulate matter is one of the hazardous pollutants in atmospheric environment which significantly impacts on climate changes and atmospheric visibility, and also seriously influences on human health, etc. This study focuses on the pollution characteristics and formation causes of PM10 and its main chemical components in Lanzhou. PM10 samples were collected for one year. Water-soluble ions and polycyclic aromatic hydrocarbons of PM10 in 2011 were analyzed to investigate the time distribution. Source of PAHs in PM10 was also apportioned. Water-soluble ions in PM10 and PM2.5 were measured in-situ by highly-time resolved instrument to reveal the diurnal pollution characteristics. The varying trend of particulate matter and its chemical components were analyzed on the condition of different weather process by Using NECP reanalysis data. HYSPLIT4, a trajectory model, were applied to analyze the backward air flow trajectories during sampling period based on the meteorological data from Global Data Assimilation System(GDAS). The effects of trajectories on PM10 and its chemical components in different seasons were investigated by using cluster analysis and pollutants concentration.The effects of temperature inversion on atmospheric pollution were researched by using of sounding data. The main conclusions were as follows.(1)The pollution of PM10 presented obvious seasonal variation. The pollution is serious in winter and mild in summer. The highest concentration of PM10 appeared in February. This is because of the contribution of coal burning and fireworks exploding during the Spring Festival. Concentrations of PM10 was higher in April with the effect of dust which caused by local and long-transportation source. Concentrations of PM10 were also higher in January, November and December. On the one hand, emissions of coal burning increased. On the other hand, the pollutants were not easy to diffusion in existence of temperature inversion.(2) Heavy pollution in Lanzhou city were two main types, namely, dust pollution and haze pollution which appeared with the high concentration of PM10 in different season. When dust pollution appeared, the main ingredients of PM10 were crust elements. The concentrations of SO42- and NO3- during dust pollution were significantly lower than that of haze pollution. Thus, the haze pollution has serious threat to human health because this kind of PM10 contains more hazardous substances.(3) The major water-soluble ions were SO42-, Ca2+, Cl- and Na+, accounting for 51.92%, 13.29%,10.73% and 5.85% respectively. Concentrations of water-soluble ions were higher in January, April, November and December than that of other months. The major ions were SO42-、 Cl- and Ca2+. The concentration of Ca2+ was distinctly higher than other ions. SO42-, NO3- and NH4+ showed similar diurnal profile with an evident increase as sun rising and a broad daytime maximum. The results of Mole ratio calculation indicated that NH4+, SO42- and NO3- primarily existed as (NH4)2SO4, (NH4HSO4) and NH4NO3. Cl- presented the bimodal pattern. The first peak appeared at 10:00. The first valley appeared at 17:00. The second peak appeared slightly at 0:00.(4) The 16 US EPA priority PAHs in PM10 were analyzed, and 11 kinds of PAHs were checked out. The concentration of total PAHs ranged from 5.13 to 658.36ng/m3 and the annual average concentration was 101.91ng/m3. The concentration of PAHs in PM10 presented the order of winter>autumn>spring>summer. PAHs with different structure have different seasonal variation, and the highest concentration appeared in winter. The PAHs sources in different seasons were mainly apportioned to transportation, coal combustion and cooking emission by using of Principal component analysis.(5) The direction of the airflow trajectory in Lanzhou were mainly along the southeast, northeast northwest, southwest and west direction, of which the larger frequency airflow trajectory were from southeast, northeast and northwest. When the airflow trajectory came from NW and NNW direction in spring and summer, the PM10 concentration was higher. The reason is that the dust particles were carried to Lanzhou by the airflow trajectory from the desert and gobi in the north of Xinjiang province and other regions. When the airflow trajectory came from the SW and W direction in autumn and winter, the PM10 concentration was higher.(6) When the airflow trajectory came from the NNE and NW direction in spring, the concentration of water-soluble ions were high except F- and NO3-. When the airflow trajectory came from the NNE direction, the concentration of total PAHs was 60ng/m3, which was much higher than that of other airflow trajectorys appeared. When the airflow trajectory came from SSE direction, SO42- has the highest concentration, and NO3- and Cl- were lower than that of the condition when airflow trajectory from NNE and N W direction. The concentration of total PAHs was low in summer. The effect of the airflow trajectory to total PAHs concentration was not obvious. When the second airflow trajectory appeared in autumn, the concentration of Na+、Cl-、 NO3-、Mg2+ and Ca2+ were high and the total PAHs was 80ng/m3, which were much higher than that of other airflow trajectorys appeared. When the airflow trajectory come from the W direction, concentrations of F-、Cl-、SO42-、K+ and Ca2+ were high. The airflow trajectory come from the NW direction, the Na+has the highest concentration and the SO42-has the lowest concentration. When the airflow trajectory came from the N direction, the NO3- has the highest concentration. When the airflow trajectory came from the S, N and W direction, the concentration of PAHs is significantly higher than that of other seasons, and the concentration of total PAHs was higher at around 160ng/m3.(7) In order to analyze the effect of temperature inversion to PM10 and its chemical components, the original daily sounding records in Yuzhong Meteorological Station were used to acquire the ground temperature inversion, heights of bottom of untouched temperature inversion and inversion intensity. The results show that there is an infirmly-steady low-air temperature inversion over Lanzhou City in the sampling period. There were temperature inversions in 292 days of one year and 214 days for the ground inversion with the average thickness of 298 m. The temperature inversion characteristic was the most remarkable with the strongest intensity, the highest occurring frequency, and the thickest ground inversion. The number of days which the Inversion intensity greater than 2.0℃/hm was 76 days and the highest intensity of inversion was 17.6℃/hm. The temperature inversion was serious especially in November and December. The intensity, heights of untouched inversion bottom and inversion thickness have comprehensive effect on PM10 concentration and its chemical component.