Pollution Characteristics Of Atmospheric Polycyclic Aromatic Hydrocarbons And PM_2.5 In Typical Cities Of Hangzhou Bay Region

Cities of China are now suffering from heavy haze pollution.It is essential to investigate the pollution characteristics of PM_2.5 and its precursors so as to reduce the impacts of haze on environment,economy and human health.Polycyclic aromatic hydrocarbons（PAHs）are a group of widespread toxic persistent organic pollutants in environment.Particulate PAHs can directly adhere to PM_2.5,and gaseous PAHs can contribute to PM_2.5 by the migration and transformation.In the dissertation,pollution levels,gas/particle partitioning,health risk and source apportionment of PAHs in different seasons and haze episodes in xiasha area of Hangzhou were investigated,and the influence of air mass transport was also analyzed.Furthermore,pollution levels and sources of water-soluble ions,carbonaceous species and elements in PM_2.5 during haze and non-haze episodes in Cixi were studied.The main conclusions of the dissertation were as follows:1.Pollution characteristics of atmospheric PAHs in xiasha area of Hangzhou（1）The concentrations of gaseous PAHs in warm season were significantly higher than those in cold season,while opposite result was observed in fine particulate PAH(PM_2.5-bound PAH)concentrations.There were no significant difference in gaseous PAH concentrations among different haze episodes.Meanwhile,the concentrations of fine particulate PAHs during haze episode（light-haze:1.63-21.7 ng/m³;heavy-haze:1.29-19.4 ng/m³）were significantly higher than those during non-haze episode（0.778-10.6 ng/m³）,and there was no significant difference in fine particulate PAH concentrations between light-haze and heavy-haze episodes.（2）There was no obvious variation in gas/particle partitioning of PAHs between haze and non-haze episodes in warm season,while PAHs had more intensified trend of partition to gaseous phase during haze episode than that during non-haze episode in cold season.With the aggravation of haze pollution,the trend of PAHs partition to gaseous phase became intensified,and the mechanism of gas/particle partitioning of PAHs changed from absorption to coexistence of adsorption and absorption.（3）The estimated lifetime cancer risk of PAH samples all exceeded the acceptable risk level,and 42%of gaseous PAH samples and 49%of fine particulate PAH samples showed serious lifetime cancer risk level.In addition,higher lifetime cancer risk was observed during haze episode,suggesting that haze pollution would result in more serious health risk to human.（4）Positive matrix factorization model and conditional probability function were applied to the source apportionment of fine particulate PAHs.The highest source contributions of fine particulate PAHs were vehicular emissions（45%）,followed by heavy oil combustion（23%）,coal and natural gas combustion（22%）,and biomass combustion（10%）.Vehicular emissions were the most considerable sources that resulted in the increase of fine particulate PAH levels during haze episode,and heavy oil combustion played an important role in the fine particulate PAH pollution.（5）The analysis of air mass back trajectories indicated that both short-and long-range air mass transports had an influence on the fine particulate PAH pollution.The air masses in cold season mainly originated from inland in north of China,where air pollution was serious.These air masses could transport with fine particulate PAHs to sampling site and result in the increase of fine particulate PAH concentrations.2.Pollution characteristics of PM_2.5 in Cixi（1）The daily average concentration of PM_2.5 in Cixi was 117 μg/m³,which was exceeded the Chinese National Ambient Air Quality Standard（GB 3095-2012;75 μg/m³）.The PM_2.5 pollution at urban and suburban sites was more serious than those at background site,which was closely related to the kinds of pollution sources distributed in urban and suburban sites.（2）The concentrations of elements,water-soluble ions and carbonaceous species in PM_2.5 significantly increased during haze episode,which were 1.07-3.36,6.03-14.39 and 1.83-1.97 times of those during non-haze episodes.（3）High enrichment factors,ranging from 100 to 10000,of elements Cu,Sn,Zn,Pb and Se were found in PM_2.5,indicating that power plant and metal manufacturing emissions were the dominant air pollution sources in Cixi.The profiles NO₃^-/SO42-ratios revealed that the contribution of stationary emissions increased during haze episode.（4）The average contribution from secondary aerosol species(SO₄^2-,NO₃^-,NH₄⁺ and secondary organic matter)was 48.7%in PM_2.5 components during haze episode,which was significantly higher than those during non-haze episodes（16.5%）.This result indicated that secondary aerosol formation was an important factor for haze formation.