Xi'an Urban Road Dust Polycyclic Aromatic Hydrocarbons In Evaluation

Polycyclic aromatic hydrocarbons (PAHs) are important environmental pollutants. They have a strong teratogenicity, carcinogenicity and mutagenicity, and are ubiquitous in the environment. Consequently, PAHs have attracted much attention and listed as "Priority Pollutants"'by many countries. Urban road dust is not only an important source of particulate matters (PM), but also a major source of PAHs to the air. Most studies of urban road dust have focused on inorganic element and elemental carbon in Xi'an. Research thus available data on PAHs in urban road dusts in Xi'an are quite limited. Although there are few studies on region profile of PAHs in settled particulate matters, little attention has been paid to atmospheric depth profile of PAHs in settled particulate matters.The aim of this thesis is to evaluate PAHs pollution in urban road dust in Xi'an with the purpose of providing efficient information which benefits to take environment assessment and protection process. At the same time, the study of depth profile of PAHs in settled particulate matters in Xi'an based on the former work in our lab is also planned.This thesis includes two chapters. The first chapter introduces the harm of PM, road dust and PAHs, and the research status of PAHs in urban road dust. The second chapter includes the following:we collected 76 samples of road dusts from 13 roads located in different areas in Xi'an; established a validate methods for analysis of 16 PAHs (including naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, dibenzo(a,h)anthracene, benzo(g,h,i)perylene, and indeno(1,2,3-cd)pyrene) and 28 elements (N, P, S, Cl, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Br, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce, Hf, Pb, and Th) in PM; we analyzed the particle size distribution, the distribution and enrichment of the elements, and the distribution, content levels, and sources of PAHs in fine particles (< 30.8μm) and courses particles (30.8μm-154μm) in urban road dusts; we also studied the content levels and depth profile of PAHs in settled particulate matters which were collected from the different floors of two buildings (B1 and B2) in Xi'an. The main results are presented as follows:(1) The detection limits for the 16 PAHs in PM ranged from 0.001μg/g to 0.04μg/g (d.w.). The contents of 16 PAHs from 6 replicate measurements of certified reference materials (soil matrix), were all in the prediction intervals of the reference materials. The average contents for all the PAHs, except for acenaphthylene, had no significant difference between measured values and certified values in 95% confidence level.(2) The study of urban road dusts in Xi'an showed that the particle size was mainly distributed between 10.0μm and 250μm, ranging from 85.0% to 93.1% (in% v/v). The road dusts were collected from downtown had slightly more coarse particles. Based on the average enrichment factors of elements, As, La, Rb, Ga, Hf, Th, Cs, Co, Y, Mn, V, Ni, Ce, Sc, Zr, Ba, and Br were slightly enriched; moderately enriched elements included Sr, Cr, and Cu; and a highly enriched elements included Pb and Zn. Vehicle wear and exhaust emissions during the transport may be the main reason for the enrichment of Sr, Cr, Cu, Pb and Zn. Total PAHs contents in urban road dusts in Xi'an ranged from 2.78μg/g to 10.4μg/g, with a mean value of 5.88μg/g. And the PAHs contents in fine particles and courses particles of the road dusts were similar. The mean value of total PAHs contents in urban road dusts in Xi'an was higher than that in Cairo (Egypt), Niteroi (Brazil), and Dunedin (New Zealand), but less than that in Dalian, Shanghai, Taichung (Taiwan) and Ulsan (South Korea). Content distributions of PAHs were mainly affected by traffic and combustion activities (including cooking and heating). Principal component analysis also showed that PAHs in urban road dusts in Xi'an originated from vehicular emissions, coal and wood combustion, and the combustion of nature gas and oil.(3) The study of depth profile of PAHs in the settled particulate matters in Xi'an showed that the total PAHs contents in settled particulate matters ranged from 3.32μg/g to 11.5μg/g, with a mean value of 6.25μg/g. Except for the 23th floor of B2, the contents of phenanthrene were highest, accounting for 30.2%-44.3% of total PAHs contents. The high levels of phenanthrene, fluoranthene and pyrene suggesting incineration was a major source of PAHs. The mean value of total PAHs contents in settled particulate matters in the study area was lower than that in Shanghai which is more prosperous. The depth profile of PAHs in settled particulate matters was due to the migration path of PM which was contaminated by PAHs. And there are many sources of PAHs in environment that might lead to a complex depth profile of PAHs.