Characteristics And Source Apportionment Of PM In Hangzhou And The Role Of Metals In Air Pollution

With the advance of urbanization all over the world,the problem of air pollution has been paid more attention.The source,formation mechanism and migration behavior of various pollutants involving the particulate matter?PM?with different particle sizes have become hot topics in the academic field.As the Internet capital of China,nowadays Hangzhou experiences a rapid development and changing.The composition and source of PM and the formation mechanism of air pollution in Hangzhou are also undergoing remarkable change.Therefore,the experiment of PM₁₀and PM₁?dynamics kinetics of particles diameter<10 microns and<1 microns?with day resolution have been collected between December 2017 and November 2018,in Hangzhou,China.Characteristics of seven metals elements?TMs:Mn,Fe,Cu,Zn,Pb,Cd and Ni?are analyzed,involving seasonal pattern and the microstructure of typical PM and TMs.The sources of particulate matter in Hangzhou are concluded using a variety of the atmospheric models;Combining with the datasets of the nearby monitoring station,main pollutants in PM and formation mechanism of haze pollution in Hangzhou are revealed.This paper then proposes a new classification of air pollution in urban area,summarizes the influencing factors and the role of metal elements.The main findings are as follows:The level of PM pollution in Hangzhou is moderate in the large-scale,which is higher than the WHO standard,and slightly lower than other first-tier cities?Beijing and Shanghai?in China.The order of TMs concentration is Fe>Zn>Pb>Ni>Mn>Cu>Cd.The seasonal variation of PM concentration is mainly followed:winter>spring>autumn>summer.The difference between months of PM₁₀ is greater than that of PM₁.The seasonal variations of different TMs are quite different,among which the concentrations of Cd and Ni are the highest in summer.Further,results of show that PM is dominated by soot particles and irregular organic substances.TMs don't dominant in PM,among which Cu,Zn,Pb,Cd and Ni mainly exist in ultra-fine particle PM₁,while coarse particle PM₁₀ contains more Fe-,Ca-and Al-related minerals.The proportion of water-soluble metal elements:in PM₁ is Pb?32%?>Zn?27%?>Fe?22%?;in PM₁₀,Zn?41%?>Pb?36%?>Fe?15%?.Fe is more soluble in PM₁ than PM₁₀,while Pb and Zn are more soluble in PM₁₀.Through the combination of positive matrix factorization?PMF?and backward trajectory model?HYDPLIT?,the sources of PM₁₀ in Hangzhou are obtained:construction/dust?48.1%?,combustion source/garbage incineration?14.7%?,non-exhaust emission?8.4%?,crustal sources?7.9%?,steel smelting industry?7.6%?,traffic exhaust emissions?6.7%?and long-range transport?6.6%?.For PM₁₀,construction dust has the highest contribution,which might come from urban construction such as subway construction,demolition of old houses and regional expansion.For PM₁,the sequence is followed:long-range transport?20.3%?,construction/dust?19.1%?,traffic exhaust emissions?18.6%?,combustion source/garbage incineration?17.9%?,steel smelting industry?14.5%?,non-exhaust emission?9.7%?.In addition,the source of long-range transport mainly includes nearby densely populated provinces?about 50%?,marine emissions?about 30%?,remote inland areas?about 10%?and others?about 10%?.Recently,the characteristics of air pollution in urban is more likely photochemical pollution.Basing on the gradually increasing occurrence of O₃,we divide the air pollution of Hangzhou into three categories:?1?Pollution dominated by O₃(AQI>100,O₃>100?g/m³,PM₁₀?70?g/m³);?2?Pollution dominated by PM(AQI>100,O₃?100?g/m³,PM₁₀>70?g/m³),and?3?pollution contributed by two of them(AQI>100,O₃>100?g/m³,PM₁₀>70?g/m³).Effect factors of the above three types of air pollution are concluded:?1?The effect of meteorological factors on air pollution is conditional:when the rainfall is between 0 and 1 mm,it almost have no cleaning effect on AQI and PM;when the rainfall is less than 1 mm,high humidity?80%⁹0%?can promote the pollution of PM and AQI but inhibit O₃.When the average wind speed is less than 2m/s,it can significantly increase PM pollution and inhibit the generation of O₃.During air pollution,ultra-fine particulate matter?PM₁?dominates,and PM₁:PM₁₀ is significantly increased under the Pollution dominated by O₃,indicating that O₃ may have a promoting effect on the accumulation of PM₁.Finally,combined with photochemical reactions,we find that Fe,Cu and water-soluble Zn are likely to have the potential to catalyze the formation of secondary inorganic aerosols.