3 research outputs found
Impacts of aerosol compositions on visibility impairment in Xi'an, China
No full textDaily particle light scattering coefficient, PM2.5 mass and chemical composition were measured in Xi'an from February to December 2009. Visibility was strongly affected by anthropogenic air pollution sources, resulting in an average visual range (VR) of 6.4 ± 4.5 km. The threshold PM2.5 mass concentration, corresponding to VR <10 km, was ∼88 μg m−3. The revised IMPROVE equation was applied to estimate chemical extinction (bext), which on average was ∼15% lower than measured bext. PM2.5 ammonium sulfate was the largest contributor, accounting for ∼40% of bext, followed by organic matter (∼24%), ammonium nitrate (∼23%), and elemental carbon (∼9%), with minor contributions from soil dust (∼3%), and NO2 (∼1%). High secondary inorganic aerosol contributions (i.e., SO42− and NO3−) were the main contributors for VR <5 km. A Positive Matrix Factorization (PMF) solution to the Chemical Mass Balance (CMB) receptor model showed that coal combustion was the dominant factor, accounting for ∼52% of the dry particle light scattering coefficient, followed by the engine exhaust factor (∼31%). Other factors included biomass burning (∼12%) and fugitive dust (∼5%).</p
Chemical composition of PM2.5 at a high–altitude regional backgroundsite over Northeast of Tibet Plateau
No full textAerosol samples were collected from a site near Qinghai Lake (QHL) on the northeastern margin of the Tibetan Plateau (TP) to investigate PM2.5 mass levels and chemical composition, especially their seasonal patterns and sources. The PM2.5 ranged from 5.7 to 149.7 μg m–3, and it was predominately crustal material (-40% on average). The combined mass of eight water–soluble inorganic ions ranged from 1.0 to 41.5 μg m–3, with the largest contributions from SO42– NO3-, and Ca2+. Low abundances of organic carbon (OC, range: 1.0 to 8.2 μg m–3) and elemental carbon (EC, 0.2 to 2.3 μg m–3) were found in QHL. Weak seasonality in the OC/EC ratio (4.5±2.0) indicated simple and stable sources for carbonaceous particles. The water–soluble ions, OC and EC accounted for ~30%, 10% and 2% of the PM2.5, respectively. Water–soluble organic carbon (WSOC, range: 0.5 to 4.3 μg m–3) accounted for 47.8% of the OC. Both OC and WSOC were positively correlated with water–soluble K+(r=0.70 and 0.73 respectively), an indicator of biomass burning. Higher WSOC and stronger correlations between WSOC and EC in spring and winter compared with summer and autumn are evidence for primary biomass burning aerosols. The concentrations of mass and major compositions were 2–10 times higher than those for some TP or continental background sites but much lower than urban areas. Compared with particles produced from burning yak dung (a presumptive source material), PM2.5 had higher SO42–/OC ratios. The higher ratios were presumed as a result of fossil fuel combustion. After excluding data for dust storms events, the relative percentages of OM, EC, K+, NH4+, NO3– and mineral dust showed little difference among seasons despite different monsoons dominated in four seasons; implying that the PM2.5 sources were relatively stable. The results from QHL evidently reflect regional cha racteristics of the aerosol.</p
Impact of Meteorological Parameters and Gaseous Pollutants on PM2.5 and PM10Mass Concentrations during 2010 in Xi’an, China
No full textMass concentrations of PM2.5 and PM10 from the six urban/rural sampling sites of Xi’an were obtained during two weeks of every month corresponding to January, April, July and October during 2010, together with the six meteorological parameters and the data of two precursors. The result showed that the average annual mass concentrations of PM2.5 and PM10 were 140.9 ± 108.9 µg m–3 and 257.8 ± 194.7 µg m–3, respectively. Basin terrain constrains the diffusion of PM2.5 and PM10 concentration spatially. High concentrations in wintertime and low concentrations in summertime are due to seasonal variations of meteorological parameters and cyclic changes of precursors (SO2 and NO2). Stepwise Multiple Linear Regression (MLR) analysis indicates that relative humidity is the main factor influencing on meteorological parameter. Entry MLR analysis suggests that SO2 from local coal-burning power plants is still the primary pollutant. Trajectory cluster results of PM2.5 at BRR indicate that the entrained urban pollutants carried by the westerly or winter monsoon forms the dominant regional pollution sources in winter and spring. Ultraviolet (UV) aerosol index verified the source and pathway of dust storm in spring.</p
