Concentrations Of PAHs In PM_2.5 And Influences Of Long-range Transport Within The Free Troposphere

Polycyclic aromatic hydrocarbons (PAHs) are major persist toxic pollutants widely dispersed in the atmosphere and the focus of governments and researchers. The sampling station is located at Mount Lu and Mount Heng to analyze the concentrations of PAHs in PM2.5· This study is focused on the concentration levels, emission sources of PAHs in PM2.5 and influences of long range transport on the environment, which provided measured data of PAH concentrations in PM2.5 in high area in southern China and theoretical basis for air pollution controls.Particulate samples from the atmosphere with diameters of less than 2.5 μm were collected at the top of Mount Lu from March to May in 2012 for analysis using a medium-volume PM air sampler. Concentrations, emission sources and influences of long-range transport were analyzed integrated with the data measured at Mount Heng. The result indicated that the total mass concentrations of ∑15 PAHs were 160.24 μg/g with a range from 63.86μg/g to 427.97μ/g. The daily concentrations varied greatly. The predominant compound was BbF with a concentration of 23.04μg/g and the least was Ace (1.46μg/g). The characteristics of seasonal variation presented an obvious fluctuation, which the concentrations of PAHs were higher in March than those in May. For individual ring concentrations,4- and 6-ring PAH concentrations were higher which contributed 52.15% to the total while the concentrations of 2-ring PAHs were the lowest accounting for only 10.18%. Levels of lower molecular weight (2-3 ring) PAHs were higher under special conditions (before rain and fog) while higher molecular weight (4-6ring) PAH concentrations were higher in sunny days. The total concentrations of PAHs in PM2.5 were lower in higher temperature conditions and higher in lower temperature environment.The total mass concentration of PAHs were 77.99μg/g ranging 20.20-500.66 μg/g at Mount Heng, which were lower than those measured at Mount Lu obviously. The most abundant compound was FluA (9.39 μg/g) and the lowest was DbA (0.99μg/g). Concentrations of individual ring PAHs were lower than those at Mount Lu and the dominant were 3- and 6-ring PAHs accounting for 51.85% of the total. Concentrations of 3- and 4-ring PAHs were similar. Under the influence of the sandstorm during sampling at Mount Heng the mass concentrations of PAHs in PM2.5 were decreased and the levels of BaA, Chr and DbA were below detections. The levels of PAHs in PM2.5 of Mount Lu and Mount Heng were low to medium comparing with other stations.Correlation analysis, diagnosis ratio analysis and principal component analysis were conducted to distinguish and identify emission sources of PAHs in PM2.5 at Mount Lu and Mount Heng. The result suggested that 3- and 4-ring PAHs were probably emitted from the same sources different from 5- and 6-ring PAHs, while 5-and 6-ring PAHs were partly from a same emissions at Mount Lu.2-ring PAHs were emitted from different emissions from others. Diagnosis ratio analysis and principal component analysis indicated that PAHs in PM2.5 were mainly emitted from fuel and biomass combustion at Mount Lu. At Mount Heng 2-ring PAHs were also produced from different sources with 3-6 ring PAHs.3- and 4-ring PAHs were from the same emission sources and 3- and 5-ring PAHs were partly emitted from a same source. PAHs with 3-ring and 6-ring were produced from different emissions while 4-and 5-ring or 4-and 6-ring were probably from the same emissions. The result of diagnosis ratio analysis and principal component analysis indicated that PAHs in PM2.5 were emitted from combustion of coal and biomass at Mount Heng, which was similar with the result at Mount Lu.The backward trajectories of 72h for special samples (higher and lower samples) were accumulated at Mount Lu and Mount Heng with Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) Model. Local emission sources had little effect on PAH concentrations while they were mainly influenced by pollutants brought through long-range transport. Mount Heng and Mount Lu were both within the free troposphere and concentrations of pollutants in high-altitude mountain site were influenced greatly within the free troposphere.