[Pollution Level and Source Apportionment of Atmospheric Particles PM2.5 in Southwest Suburb of Chengdu in Spring].

In order to understand the characteristics of PM2.5 pollution in the atmosphere of Chengdu southwest suburb, PM2.5 particles in Chengdu southwest suburb were collected and analyzed from March 18 to March 31st, 2015. The results showed that the daily average concentration of PM2.5 in the southwest suburb of Chengdu reached 121.21 µg · m⁻³, and the average daily concentration of 24 samples in 31 PM2.5 samples was over 75 µg · m⁻³, the daily excessive rate was 77%, indicating the PM2.5 pollution in the study area was serious in March. When studying the relationship between atmospheric and meteorological factors, it was found that there was a significant index correlation between PM2.5 concentration and atmospheric visibility, and it had a positive correlation with temperature and humidity, but the correlation was not obvious. NH4⁺ (16.24%), SO4²- (12.58%) and NO3⁻ (9.91%) were dominant in PM2.5 The ratio of NO3⁻/SO4²â» was 0.77, which indicated that the pollution of stationary sources in the southwest suburb was more severe than that of mobile sources. Organic carbon (OC)/elemental carbon (EC) ratios were higher than 2, which indicated the existence of second organic carbon (SOC). Using OC/EC ratio method to estimate the concentration of SOC, it was found that the average concentration of SOC in the southwest suburb of Chengdu in March was 3.49 µ · m⁻³, and the contribution rate of OC was 20.6%, which showed that the main source of OC in the southwest suburb of Chengdu was primary discharge. The correlation analysis of OC and EC showed that the correlation coefficient reached 0.95, indicating that the OC and EC sources were similar and relatively stable, and there was a great impact of local source emissions on Chengdu southwest suburb in spring, and primary discharge played a dominant role, while the contribution of SOC to OC was relatively small, which was consistent with the SOC characteristics obtained by estimation. Using principal component analysis method to analyze the sources of PM2.5 in the southwest of Chengdu, it was found that the main pollution sources of PM2.5 in southwest suburb of Chengdu were coal burning and biomass burning, secondary nitrate/sulfate, soil and dust, vehicle emissions, electronic production source, and mechanical processing source.

[Characteristics of Elements and Potential Ecological Risk Assessment of Heavy Metals in PM2.5 at the Southwest Suburb of Chengdu in Spring].

PM2.5 samples were collected at the southwest suburb of Chengdu in spring (in May 2012 and 2014). The mass concentrations of PM2.5 were determined by the weight method, and 24 chemical elements in PM2.5 were analyzed by XRF. To study the pollution characteristics and sources of chemical elements, and the potential ecological risk of heavy metals in PM2.5, the Geo-accumulation Index, Enrichment Factor, and Potential Ecological Risk Index methods were applied, respectively. The results indicated that the mass concentrations of PM2.5 in spring at the southwest suburb of Chengdu were very high, compared with American EPA's Standard and National Standard level-Ⅱ. The detection of chemical element composition in PM2.5 showed that K and S were the main elements, whereas the contents of Ga, Cs, Co, Cd, and V were the lowest. The differences of elemental concentrations in PM2.5 showed relatively large differences, when compared with domestic and foreign representative cities. Se, Cd, As, Br, S, Pb, Cl and Zn were present at an extremely high level of geo-accumulation degree, which revealed that the pollution coming from human activities was serious. The analysis results of enrichment factor showed that Se, Cd, As, Br, Cl, Pb, Zn and S elements were highly enriched or hyper accumulated, Cu, Cs, Ni, Ga and Co elements were moderately enriched, and they were mainly from human activities rather than soil dust. Cr, Mn, Ca and V elements were mildly enriched, and they were from both natural sources and human activities. Na, Ti, Al, Si and Mg elements were scarcely enriched, and they were mainly from natural sources. The ecological risk assessment of heavy metals showed that the order of potential ecological risk inedx of heavy metals in PM2.5 was Cd > As > Pb > Cu > Zn > Ni > Co > Cr > Mn > V > Ti, while the ecological harm degree of Cd was extremely strong, and the whole potential ecological risk degree was very strong.