Chemical Characterization Of PM_2.5 And PM₁₀ Atmospheric Aerosols In Zhengzhou, China

With the rapid urbanization and industrialization, fossil fuel consumption in our country is continuously increasing, which causes the environmental deterioration day by day. This has seriously threatened people's health. Particulate is the main component of air pollution and its harm to human body has already been proved by epidemiology. The extent of particulate's harm is pertinent to the aerodynamic diameter, chemical composition and the category of the source emission.From Oct 2009 to Aug 2010, the study employed four-channel sampling instrument (TH-16A) in the Zhengzhou urban site and the samples were carried out for particulates PM2.5 and PM10 to analyze the regular pattern of their mass density. The same things were done in the Zhengzhou suburban site from Jan 2010 to Nov 2010 by TE-6070D. Component analysis was conducted for the samples of the urban site and PM2.5 samples collected in the suburban site through water soluble ions (Dionex ICS-90 Ion Chromatogram), elemental carbon (EC) and organic carbon (OC).The results obtained from the Zhengzhou urban site shows that the mass density of PM2.5 and PM10 has significant changes in different seasons. The highest value appears in autumn, the lower value is in winter and the lowest value is in summer. The density change of PM2.5 and PM10 has a good correlation (R2=0.86). In the 54 groups of samples, the mass density of PM2.5 exceeds the standard value and reaches the ratio 100% and the PM10 of 59%. The contents of water soluble ions SO42-,NO3-and NH4+ are of the first three highest ions in particulates and they make up of 43.6% PM2.5 and 35.6% PM10 respectively. Most of the water soluble ions mainly exist in the fine particles, especially the secondary particles SO42-,NO3- and NH4+. On the contrary, the SO42-,NO3- and NH4+ are almost in the coarse particles. NH4+ and NO3-, NH4+ and SO42- and NO3- and SO42- have good correlations (which are of 0.841, 0.909 and 0.730 in PM2.5; and are of 0.872,0.905 and 0.799 in PM10). The above analysis presents that the secondary particles in particulates are mainly in the form of NH4NO3 and (NH4)2SO4. Besides Ca2+ and Mg2+, K+ and Cl- have great correlations, too. The result of pH analysis shows that particulates are all acidity. OC and EC mainly exist in fine particles.The correlation of OC and EC changes with seasons, the best in summer and the worst in spring. The results show the sources of OC and EC are similar in summer, but different in spring. The average values of OC/EC in PM2.5 and PM10 are 6.86 and 6.02, which proves that particulates in Zhengzhou urban site have the critical secondary pollution.The results obtained in the Zhengzhou suburban site are similar to that in the urban site. In 49 samples, PM2.5 and PM10 exceed the standard value by 100% and 77% separately. The mass density of PM2.5 and PM10 also has good correlation (R2=0.90). Secondary particles which contain SO42-, NO3- and NH4+ consist of 40.27% of the whole mass, and they have good correlations with one another so that they have the same sources. The K+, Cl- and F- have good correlations because of the same combustion sources. The same things were done in Mg2+ and Ca2+, which may be come from soil and building dust. The correlation between OC and EC demonstrated well in summer and appears bad in winter. This phenomenon may be relevant to the coal-burning for the inhabitant round in winter. The average value of OC/EC is 6.74, which proves that the secondary pollution of Zhengzhou suburban site is also severe. The mass density of PAHs in PM2.5 is much higher in winter than in other seasons, which is identical to the study result in many northern cities. The PAHs of 4-6 rings have a higher content in PM2.5, accounting for its 59.70%. In winter, the density of Benz (a) pyrene which has high carcinogenicity reachs 17.44 ng/m3, which is 10 ng/m3 more than national standard, and it is threatening people's health. The sources of PAHs are identified by different specific values, and the results show the main source of PM2.5 in Zhengzhou suburban site is the composite pollution of coal-burning and vehicles.