RESUMO
To study the characteristics and sources of PM2.5 pollution in Taiyuan urban area in winter, PM2.5 and its chemical components (water-soluble ions, carbon components, and trace elements) and gaseous pollutants (SO2, NO2) were monitored by online instruments in January 2017. Combined with meteorological data, the characteristics of PM2.5 and its chemical components were analyzed. Also, source apportionment of PM2.5 was conducted by using positive matrix factorization (PMF). The results showed that the mean mass concentration of PM2.5 on polluted days (239.92 µg·m-3) was 5.70 times as much as that on clean days. The concentrations of the main chemical components of PM2.5 on polluted days, SO42-, NO3-, NH4+, Cl-, OC, and EC, were 7.04, 5.76, 6.51, 5.62, 4.06, and 4.70 times their respective values on clean days. The sulfur oxidation ratios (SOR) and the nitrogen oxidation ratios (NOR) on polluted days were 0.12 and 0.19, respectively, which were higher than those in clean days, indicating that secondary transformation was more significant on polluted days. The results of the PMF source apportionment showed that the contributions of secondary sources (35.06%), coal combustion (30.19%), and vehicle emissions (24.25%) were higher on polluted days than on clean days, with increases of 18.03%, 7.39% and 2.10%, respectively. Thus, air pollution control strategies should pay more attention to controlling secondary source precursors on the basis of controlling the primary emission sources on polluted days.
RESUMO
To study the characteristics and sources of trace metals in PM2.5 during wintertime in Beijing, PM2.5 samples were collected from December 2014 to January 2015 by a middle volume sampler in the urban area of Beijing for 30 consecutive days. The mass concentration of PM2.5 was measured by filter membrane weighting method, and 16 kinds of trace metals were determined by inductively couple plasma-mass spectrometry (ICP-MS). In addition, the pollution characteristics and sources of trace metals were analyzed by enrichment factor (EF) method and factor analysis, respectively. The results showed that the concentrations of five elements (i. e. K, Ca, Fe, Al and Mg) accounted for 90.7% of the total metal elements. The concentrations of the metal elements changed obviously between day and night. Compared with daytime, crustal elements like Mg and Al decreased by more than 30% while anthropogenic elements like Cu and Pb increased by more than 40% in nighttime. Although the concentrations of metal elements increased by nearly one time in heavy pollution days compared with clean days, the mass percent of which in PM2.5 decreased from 10.9% in clean days to 4.6% in heavy pollution days. This result suggested the accumulation of metal elements in heavy pollution days had a minor contribution to the increased mass concentration of PM2.5. As the pollution episode progressed, anthropogenic elements (Cu,Zn,As,Se,Ag and Cd) increased faster than crustal elements (Al,Mg,Ca,Mn and Fe), which showed ratios ranging from 2.9 to 5.3 for anthropogenic elements and ratios ranging from 1.2 to 1.8 for crustal elements, when compared between heavy pollution days and clean days. In addition, the EF value of anthropogenic elements was also increased in the pollution days, indicating the concentrations of these elements was further influenced by the anthropogenic sources. Factor analysis showed that metal elements of PM2.5 during wintertime of Beijing were mainly from coal combustion and biomass burning, motor vehicle and industry emissions, and re-suspension of road dust, with the contributions of 34.2%,25.5% and 17.1%, respectively.
