| The study of atmospheric polycyclic aromatic hydrocarbons(PAHs)in northeastern Tibetan Plateau with fragile ecological environment and complex atmospheric circulation system is blank.To understand the characteristics and sources of PAHs in the atmosphere of the northeastern Tibetan Plateau,we have continuously monitored levels in the central Qilian Mountain.We collected 45-pair(particle+gas)samples using active air samplers.This study clarifies the concentration and seasonal variation of PAHs in the northern Tibetan Plateau,which is conducive to understanding the atmospheric transport process and fate of pollutants.The background site of Qilian Mountains located in the Silk Road economic belt has the value and significance of long-term observation of pollutants.(1)The atmosphere of the middle Qilian Mountains is dominated by 3 ring PAHs.The average atmospheric concentration of PAHs at the background site is 2015pg/m~3,and the average dry deposition flux is 3.86μg/m~2/d.The PAHs pollution levels in the northern part of the Qinghai-Tibet Plateau are lower than those in the southern part of the Plateau due to the nearby pollution sources and the transport conditions of forest fire emissions.(2)The seasonal variation of PAHs concentration was low in warm season and high in cold season under the influence of emission sources and seasonal differences.The seasonal variation of PAHs with different phase states and ring numbers is also different,which may be caused by the difference of emission sources.In addition,through multiple linear regression analysis and Pearson correlation analysis,meteorological factors also have a significant impact on PAHs.During the cold season,low temperatures and low wind speeds can cause pollutants to accumulate locally.For the whole sampling period,the relative humidity of the environment is the most important factor affecting the change of PAHs.The correlation between gas phase PAHs and atmospheric temperature is not significant,while the correlation between particle phase PAHs and atmospheric temperature is very high and negative.(3)In this study,source analysis of PAHs was carried out by using specific substance diagnostic ratio method,PMF model and principal component analysis.Combustion sources,including coal burning,grassland,wood and biomass burning,are the main sources of pollution in spring and winter.Among them,coal burning pollution and wood burning pollution have a particularly strong impact on spring and winter.The main sources of PAHs pollution in summer and autumn are vehicle exhaust emissions,including diesel vehicle emissions and gasoline vehicle emissions.In addition,through the analysis of the composition of energy consumption in the provinces and autonomous regions of northwest China,it is confirmed that the contribution sources of PAHs are mainly coal combustion pollution and automobile exhaust pollution.(4)Qilian Mountain is located in the key position of the Silk Road Economic belt,so it is very important to study the pollutant transport process in this region.In this study,the transport of PAHs in the middle qilian Mountains was analyzed using 12-hour and 120-hour backward air mass tracks.Potential source contribution factor analysis was used to locate the near source pollution of PAHs,and concentration weight trajectory analysis was used to locate the long distance transport path of pollutants.The results show that the transport of PAHs has seasonal differences,mainly affected by westerlies,especially in winter.Anthropogenic emission of near source pollution has a great influence,and the source area is mainly distributed along the towns and traffic lines in the west and north of the sampling site.The sources of remote pollution are mainly distributed in western and central China,central Asian countries bordering western China and northern India.In addition to natural factors,the main sources of PAHs are also closely related to human conditions such as population distribution,urban layout and traffic route distribution. |
PDF Full Text Request