Study On Volatile Organic Compounds(VOCs) And Particulate Matter In Urban Atmosphere Over The Gan-Xin Region

In China,there is a significant emission burden for volatile organic compounds（VOCs）and particulate matter（PM）,which are important precursors and components of combined urban air pollution.As a result of their ongoing reactivity and transmission in the atmosphere,they worsen air quality,contribute to climate change,and endanger human health.The atmospheric environment in Northwest China is unique due to the high amount of sand and dust and low humidity,and the degree of secondary pollution has been increasing in recent years.Previous studies are less concerned with VOCs and PM in this environment,and there is also a lack of scientific understanding of the mechanisms of secondary pollution formation from VOCs in sandy and dusty environments.This paper is an important supplement to the previous studies by conducting a systematic study for cities in Northwest Gansu Province and Xinjiang Uygur Autonomous Region（the Gan-Xin region）,which is of great scientific significance and practical value for the prevention and control of compound atmospheric pollution and the health protection of residents in China.In this paper,VOCs and three particle sizes of PM(PM₁₀,PM_2.5 and PM₁)were sampled and analyzed in the atmosphere of 13 cities in Gan-Xin Region based on proton transfer reaction mass spectrometry（PTR-MS）and the collection and analysis of particulate matter.The pollution characteristics,sources and environmental health effects of VOCs and PM in the atmosphere of the Gan-Xin cities were investigated by simulation studies with models such as receptor model,Lagrangian dispersion model and health risk assessment.The main results are as follows:1.The pollution characteristics of VOCs and components in urban atmosphere over Gan-Xin Region were elucidated.The results showed that the average concentration of total VOCs（TVOCs）in the atmosphere was 41.84±7.56 ppbv,showing a pattern of higher daytime concentrations than nighttime,indicating that the influence of daytime anthropogenic production and living.Oxygenated VOCs（OVOCs）were important components of VOCs,where high concentrations of methanol were related to their background concentrations and the plant-oriented air masses at each site.The total concentrations of VOCs were higher than those in other cities at home and abroad,mainly methanol and acetaldehyde were higher,while the aromatic hydrocarbons were lower than those in other cities.2.The pollution characteristics of PM and its components（water-soluble inorganic ions,carbonaceous aerosols and inorganic elements）in the urban atmosphere over the Gan-Xin Region were elucidated.The results showed that the average mass concentrations of PM₁₀,PM_2.5 and PM₁ in the atmosphere were 139.39±32.63μg/m³,77.66±25.39μg/m³ and 44.76±17.59μg/m³,respectively.The concentration of PM in the daytime was lower than that at night,indicating that it was affected by a low boundary layer and heavy truck emissions at night.Inorganic ions and mineral dust were the main types of PM in the cities of this region.PM pollution is divided into two types:anthropogenic pollution and dust pollution.Priority reduction of sulfate,nitrate and ammonium（SNA）and Ca²⁺can effectively reduce the occurrence of PM pollution.3.The local and remote sources of VOCs and PM in the urban atmosphere over the Gan-Xin Region were analyzed.The results showed that there were eight sources of atmospheric VOCs,including residential biofuels+waste treatment,biogenic sources,mixed industrial processes-coal,secondary formation,biomass combustion,mixed industrial processes-fuel,vehicle exhaust and solvent use.Local sources and long-distance transport contributed 67.5%and 32.5%of VOC pollution,respectively.There were six sources of atmospheric PM,including secondary formation,dust,transportation,coal combustion,metal industry and biomass combustion.Local sources and long-distance transport contributed 57.5%and 42.5%of PM pollution,respectively.4.The effects of VOCs on ozone（O₃）and secondary organic aerosols（SOA）in the urban atmosphere over the Gan-Xin Region were revealed.The results showed that the main VOC components forming O₃ were acetaldehyde,trimethylbenzene,propylene,isoprene and methanol.The main sources of O₃ formation were residential biofuel use and waste disposal,mixed industrial process-fuel and solvent use.The main VOC components forming SOA were C₁₀-aromatic hydrocarbons,xylene and styrene at low NOx concentrations,but benzene,C₁₀-aromatic hydrocarbons,and toluene at high NOx concentrations.The main sources of SOA were vehicle exhaust and solvent use.By fitting the estimated and measured values,it was concluded that VOC oxidations could explain 6.1-20.7%of SOA formation.5.The health risks of VOCs and heavy metals in PM in the urban atmosphere over Gan-Xin Region were assessed.The results showed that the non-carcinogenic risk of VOCs was significant,and the carcinogenic risk was at an acceptable level,and the non-carcinogenic risk of acetaldehyde and the carcinogenic risk of naphthalene were higher.The non-carcinogenic and carcinogenic risks of heavy metals in PM are significant.The carcinogenic and non-carcinogenic risks of PM₁₀ were higher than those of PM_2.5,and the non-carcinogenic risk of Mn and the carcinogenic risk of As were higher.In summary,there were different levels of pollution from VOCs and PM in the urban atmosphere over the Gan-Xin Region with obvious spatial and temporal patterns.The contribution of local sources of VOCs and PM was relatively more important,and the contribution of sandy and dusty environments to the oxidation reaction of VOCs might be limited.To reduce the formation of secondary pollution（O₃ and SOA）,priority control of VOC components acetaldehyde and benzene,as well as sources such as residential biofuel use+waste disposal and vehicle exhaust is needed.To reduce the health risk of toxic pollution to the population,priority control of acetaldehyde,naphthalene,Mn and As elements is needed.