Particulate Size Distribution And Sources Evaluation Of N-alkanes During A Persistent Haze Episode In Chaohu Lake Watershed

With the rapid socioeconomic development and intensification of anthropogenic activities, air pollution is becoming a big environment-related challenge for all people over the world. Chaohu Lake region is an important economical development zone in Eastern China. Recently, deterioration of air quality around Chaohu Lake, specially caused by haze episode has significantly affected people life and human health. As well known, atmospheric particle is a vital factor controlling haze. It is a common approach using molecular markers to investigate the sources of aerosol and further to understand the formation of haze.In the present study, aerosol samples with eight size fractions were collected from 12 sites around Chaohu Lake using a eight-stage cascade impactor to determine the concentrations of n-alkanes (from C₁₀～C₃₆). Compositional distribution and size-distribution of n-alkanes were investigated to evaluate their potential sources. Furthermore, hourly concentrations of PM_2.5, PM₁₀, NO₂, SO₂, CO and O3 in 10 monitoring stations in Hefei recorded during sampling months were exacted from a public data platform. Results show:（1） Air quality of Hefei was seriously influenced by PM_2.5, followed by PM₁₀. Within 80% and 56% of days, daily average concentrations of PM_2.5 and PM₁₀ were higher than the corresponding National Air Quality Standards of China. While air pollution caused by NO₂, SO₂, CO and O3 is ignorable. The concentrations of all pollutants appeared significantly temporal and spatial variablities with more serious pollution in urban areas, and air was most polluted during December of 2014. Heavy haze episode occurred during October to December in 2014 based upon the estimate of atmospheric visibility. Thus, sampling period was characterized by a persistent haze episode.（2） The total concentration of n-alkanes in aerosol around Chaohu Lake varied from 402-3040 ng/m³ with an arithmetic mean of 1460 ±1000 ng/m³. The maximum value was observed in Sanhe town, which is a typical tourism area, local commercial cooking was suspected as a potential source. There is not significant spatial variation on the concentration of n-alkanes, and the concentrations in urban areas did not appeared clearly higher concentration comparing with suburban and rural areas. Thus these results reflect the atmospheric particulate pollution during persistent haze episode was even around Chaohu Lake.（3） Size distribution of n-alkanes at individual sampling site largely varied, n-alkane predominantly accumulated fine particles for the sites from surrounding counties and the towns, but aliphatic hydrocarbon tended high accumulation in coarse particles for the sites from urban areas. However, the distributions between fine-coarse particles were significantly controlled by the number of carbon atom in each sampling site, suggesting various sources.（4） Geometric mean diameter of n-alkanes around Chaohu Lake was estimated at 2.61 ± 1.21 μm with the maximum being observed at new campus of Hefei University of Technology. Average geometric standard deviation of n-alkanes was 0.43 ± 0.06 μm. Geometric mean diameter of individual n-alkane homologue appeared significantly positive correlation against their saturated vapor pressure, but geometric standard deviation tended a negative correlation against their saturated vapor pressure. Therefore, the size distribution of n-alkanes was affected by their physical-chemical properties.（5） Compositional distribution of n-alkanes in aerosol collected around Chaohu Lake suggests anthropogenic sources with CPI close to 1.0 and the maximum CPI value was obtained at new campus of Hefei University of Technology. Approximately 15.9 =1=7.0% of n-alkanes in aerosol around Chaohu Lake were derived from high plant using the estimate of %waxC_n.