Pollution Characteristics And Transportation Effects Of Atmospheric Mercury At Coastal And Inland Urban Sites Of Eastern China

Atmospheric mercury is a global pollutant,which has attracted worldwide attention due to its persistence,long-range transport,high biotoxicity and bioaccumulation in food chains.China is the largest contributor to anthropogenic mercury emissions in the world,due to the abundant consumption of mercury ore combined with rapid industrialization and urbanization.As one of the regions with high population density,high degree of industrialization and severe environmental pollution in China,eastern China has aroused wide public concern,in which the anthropogenic source emissions could account for more than half of the China’s total emissions.However,research on the characteristics and sources of atmospheric mercury pollution there remained scarce.Due to the differences in geographical location,human activities,pollution sources and meteorological conditions,the temporal-spatial distribution and the variation characteristics of atmospheric mercury are very complex and diverse.Coastal urban areas are under the influence of both intensive inland anthropogenic sources and marine air masses,which could change atmospheric composition and subsequently influence the formation and redistribution of total gaseous mercury(TGM)in coastal areas.To understand the pollution characteristics of atmospheric mercury in coastal and inland urban areas in eastern China,comprehensive observation campaigns of atmospheric mercury were carried out in coastal Qingdao and urban Jinan.This study analyzed the distribution and pollution characteristics of TGM concentrations at a coastal site of Qingdao and an inland urban site of Jinan,explored the contribution of wintertime heating activities to atmospheric mercury pollution in eastern China,and analyzed the effects of sea and land breeze on TGM concentrations in coastal regions.Influences of regional transport on TGM concentrations were analyzed using Hybrid Single Particle Lagrangian Integrated Trajectory(HYSPLIT)model and the major potential emission source regions were simulated with potential source contribution function(PSCF).Major influence factors of TGM and particulate-bound mercury(PBM)concentrations were identified using principle components analysis(PCA)and positive matrix factorization(PMF).In addition,episodes studies on the effects of haze,dust and typhoon were carried out to further elucidate the effects of key factors on atmospheric mercury concentrations.Following is the main results of this study.(1)Studies on the characteristics of TGM concentrations and the influence of sea-land breeze in coastal Qingdao showed that the TGM concentrations ranged from 0.59 to 24.46 ng m-3 with a mean of 2.28(±0.87)ng m-3.This mean value was much higher than those measured over the adjacent open seas in China,and was～1.5 times higher than the Northern Hemispheric background concentration.TGM concentrations exhibited a strong dependence on wind directions with an average value of 2.41 ng m-3 under offshore wind,～24%larger than that under onshore wind.The TGM diurnal cycle exhibited a daily peak in the early morning and minimum at 15:00 in the afternoon,resulting mainly from sea-land breeze circulation and boundary layer height variations.The daily minimum TGM concentrations with the occurrence of sea-land breeze circulation were higher than those without.Correlation analysis with criteria air pollutants suggested that mobile combustion was a major anthropogenic emission source to TGM in coastal Qingdao,and coal-fired power plants became a significant contributor in winter.PSCF analysis attributed high TGM concentrations to regional transport from anthropogenic emission sources in the neighboring cities or provinces in eastern China.(2)Studies on the characteristics of TGM concentration and the influence of wintertime heating in urban Jinan showed that TGM concentrations were averaged at 4.91±3.66 ng m-3 ranging from 0.31 to 46.36 ng m-3.The mean TGM concentration was comparable to those in other inland urban sites of China,slightly higher than those at coastal sites of China,and significantly higher than the background concentrations in Northern Hemispheric and high-elevation background sites in China.TGM in Jinan exhibited a distinct diurnal pattern with a peak in the morning and a minimum in the afternoon on less polluted days,which was predominantly influenced by the variation in boundary layer height.In contrast,a singular peak of TGM concentrations was observed at midday on heavily polluted days during the heating period,which was mainly influenced by anthropogenic emissions.Wintertime heating is an important factor influencing atmospheric mercury concentrations in urban Jinan.The mean TGM concentration was 5.92 ng m-3 during the heating period,almost twice higher than that during the non-heating periods.Combustion source emissions as well as meteorological factors such as wind direction and speed made major contributions to ambient TGM concentrations in Jinan urban area.Additionally,the TGM concentrations in Jinan were affected by the distribution of local emission sources.Transport from southern part of Shandong Province contributed to the most of the atmospheric mercury levels observed in Jinan due to the highest TGM concentration of air mass polluted by numerous industrial emission sources.(3)The size distribution results of particulate-bound mercury showed that PBM is mainly concentrated in fine particulate matters in Jinan.PBM in particle size range less than 1.8 μm contributed approximately 60%of the total PBM(∑PHg)and 68%in particle size range less than 3.2 μm.To further analyze the pollution characteristics of PBM2 5 in Jinan,the results showed that the average concentration of PBM2.5was 452±433 pg m-3,which was 13%lower than the observed PBM2.5 in the year of 2014-2015.However,the mean PBM2.5 concentration was above the medium level compared with those in other cities of China and was nearly two orders of magnitude higher than the observed values in North America and Europe.In addition,the mercury mass content in PM2.5 of Jinan is considerably higher than the averaged mercury contents in coal and soil in Shandong Province.This indicated that atmospheric fine particles have a strong enrichment ability to mercury,and the deposition of atmospheric mercury particles could aggravate the mercury pollution in soil.Increased emissions from wintertime heating activities could aggravate the PBM pollution in Jinan.Similar with TGM,the mean PBM2 5 concentration during heating period in Jinan is 599 pg m-3,twice higher than those during the non-heating period(291 pg m-3).This study also found a significant correlation between the concentrations of PBM2.5 and TGM during the heating period,while no significant correlation during the non-heating period.PCA analysis and PMF source analysis further suggested that the PBM2.5 and TGM during the heating period shared the common coal combustion sources and industrial sources,while not exactly the same source between PBM2.5 and TGM during the non-heating period.In addition to industrial source,dust and biomass combustion also have a great influence on PBM2.5 during the non-heating period.(4)In this study,severe air pollution induced by weather events such as haze,Asian dust storm,typhoon frequently occurred during the observation of atmospheric mercury in coastal areas of Qingdao and urban areas of Jinan.This study showed that the concentrations of TGM and PBM2 5 observed in the urban area in Jinan significantly increased during the haze episodes.On haze days,anthropogenic emissions and stationary weather conditions could result in the significant accumulations of TGM and PBM2.5.Foggy days after heavy pollution may provide conditions conducive to secondary formation of PBM2.5,resulting in increased PBM2.5 concentrations.Different from that in Jinan,the haze in the coastal area of Qingdao mainly comes from the polluted area or the air mass transported by the polluted area,which resulted in the increase of TGM concentrations,aggravating the atmospheric mercury pollution in the coastal area of Qingdao.The study found that dilution from the enhanced boundary layer height and relatively clean marine air masses could reduce the TGM concentrations by 30%during the haze episodes.Unlike haze events,which occurred concurrently with weak wind conditions,Asian dust storms occurred with strong wind accompanied by high concentrations of coarse particles and typhoon weather is accompanied by strong winds and heavy rain.Hence dust and typhoon events could have different effects on atmospheric Hg species from haze events.During a dust storm episode,concentrations of TGM and PBM2 5 notably decreased,while the PBM concentrations significantly increased in the coarse particle size range of 10-18 μm.On the one hand,it could be ascribed to the adsorption and distribution of mercury between fine and coarse particles.On the other hand,it is also an important reason that coarse particles from desert were transported through heavily polluted areas such as Beijing-Tianjin-Hebei region under the effects of Asian dust conditions,which were polluted by the air masses there.Prior to the arrival of a typhoon,TGM concentrations rose sharply due to transport from polluted regions in East Asia as well as downdrafts at the front and lateral edges of a typhoon,whereas dropped to a mean concentration of 1.57 ng m-3,comparable to the globally background value,as the typhoon arrived.Frequently occurring typhoons contributed to the high TGM episodes in summer in coastal areas of Qingdao.This research used the observation of atmospheric mercury at Qingdao coastal site and Jinan urban site,contributed to a better understanding of atmospheric mercury pollution levels,the pollution characteristics and influence of regional transport in coastal and inland urban environments in eastern China.In addition,the high enrichment of PBM in PM2.5 was found in Jinan,leading to potential environmental risk.Wintertime heating activities contributed significantly to the atmospheric mercury concentrations in urban areas and sea-land breeze circulation could lead to the rise of atmospheric mercury concentrations in coastal areas.The results of this study provide data support for filling the gaps in atmospheric mercury research in inland and coastal areas,which are also of significant importance for evaluating human activities contributions to atmospheric mercury and further providing theoretical basis for atmospheric mercury pollution control.