Chemical Composition Characteristics And Source Apportionment Of PM_2.5 In Zhengzhou

The rapid development of economy and urbanization has led to atmospheric environmental pollution in China increasingly severe. Haze weather occurred frequently, and atmospheric fine particulate matter(PM2.5) pollution has become more and more serious. PM2.5 has become the primary air pollutant in China’s large and medium–sized cities. Zhengzhou, the main city in central China, has been found to be one of the serious PM2.5 pollution cities in China. Carrying out the research on chemical characteristics and source apportionment of fine particles has become the key of improvement of air quality and achievement of the PM2.5 standard in Zhengzhou city.In this research, PM2.5 were sampled from 2011 to 2013(n = 172) in Zhengzhou city and water–soluble inorganic ions, organic carbon, elemental carbon as well as polycyclic aromatic hydrocarbons(PAHs) components were analyzed to investigate the pollution levels of PM2.5 and its components. The seasonal and annual variability of PM2.5 and its components, the mass concentration contributions of individual components to PM2.5 and its health and environmental impacts were also studied in this thesis. Through the use of positive matrix factorization(PMF) model, source apportionment of PM2.5 in Zhengzhou city was also conducted.Using the empirical formula of the Interagency Monitoring of Protected Visual Environments project, the light extinction contributions of PM2.5 components were estimated to find out the species which had the maximum impact on visibility. Moreover, the mass concentration and light extinction contribution of secondary components of PM2.5 were investigated. Three persistent heavy pollution events in winter of 2011 to 2013 were analyzed; pollution characteristics of PM2.5 and its components during episode period and non–episode period were comparatively analyzed. The backward trajectory model(HYSPLIT) was used to analyze the possible effects of air mass.The annual mean concentrations of PM2.5 were 186, 182 and 218 μg/m3 for 2011, 2012 and 2013 respectively, which were 5–6 times larger than the annual standard value(35 μg/m3) of Chinese national ambient air quality standard. So, the pollution situation of PM2.5 in Zhengzhou is very serious.It can be seen from the annual average contributions of individual species to PM2.5 of 2011 to 2013 that organic matter(OM) in PM2.5 contributed the largest proportion, the percentage was(18–26%), followed by: SO42–(14–19%), NO3–(10–11%), NH4+(8–9%) and EC(3%). From 2011 to 2013, the contribution of OM grew 8% and the contribution of SO42– grew 3%, showing that organic components and sulfate precursor emissions increased. Therefore, measures need to be taken to reduce the emission of OC and prevent OC pollution aggravates. Mass concentration ratios of NO3–/SO42– were within 0.3–1.1, indicated that the stationary source emissions was the main emissions source of fine particles in Zhengzhou city. Obvious enrichment of SOC in autumn and winter were probably due to biomass burning and increased coal–burning emissions in autumn and winter.The secondary species investigations showed that secondary aerosols play an important role both in the total PM2.5 mass and the visibility deterioration effect. Secondary inorganic aerosol(SO42– + NO3– +NH4+) accounted for 33–45% of total PM2.5 mass, with secondary organic aerosol accounting for 4–21%. The secondary aerosol((NH4)2SO4 + NH4NO3 + SOM) accounted for 80% of the total light extinction contributions.(NH4)2SO4 and NH4NO3 are the two main factors that influence the visibility deterioration of Zhengzhou city. In order to achieve the targets of PM2.5 control, measures need to be taken to control NOx, SO2, NH3 and VOCs emissions. The results of source apportionment illustrated that the main source to PM2.5 were: coal(29%); motor vehicle(26%); dust(21%); secondary aerosol(17%) and biomass burning(4%).The total mass concentration of 16 PAHs in PM2.5 from 2011 to 2013 were in the range of 7–961 ng/m3, with a 3–year average of 174 ng/m3. Seasonal variations of PAHs showed a clear trend of winter > autumn > spring > summer. The major species were Bb F, Chry, Flt, Bk F, Ba A, Pyr and Ind, accounting for 58–82%(average: 73%) of the 16 PAHs, which reflected the influence of coal combustion and vehicle exhaust. Ratios of S16PAHs/PM2.5 varied with the season and PM2.5 concentrations. The 3–year average concentration of Benzo[a]pyrene was 9.4 ng/m3, larger than the Chinese air Ba P standard(annual average 1.0 ng/m3). The annual mean values of ∑16PAHTEQ in PM2.5 were 22, 19 and 28 ng/m3 for 2011, 2012 and 2013, respectively, reflecting a serious hidden danger to health. Diagnose ratios and PMF results showed contribution from coal, vehicle, coking plants and biomass burning.The average value of PM2.5 concentrations during the events were up to 453 μg/m3, much higher than the dates during non–event days(180 μg/m3). The average mass concentrations of OC、EC、SO42–、NO3– and NH4+ during the three events days were higher than those in the non–events days. Proportions of each component in PM2.5 during events days changed, presumable related to the different pollutants(or precursor) emissions from local and transmission from regional. The ratio of ∑16PAHs/PM2.5 decreased as PM2.5 concentration increased. The ratios of ∑16PAHs/PM2.5 during the event days were lower than those of non–events days, which were probable due to increasing of PAHs(in ng level) far less than increasing of PM2.5(in μg level).