Study On Pollution Characteristics And The Influence Of Volatile Organic Compounds In Coal Chemical Industry And Wastewater Treatment

In recent years,the problem of regional atmospheric combined pollution characterized by fine particulate matter(PM_2.5)and ozone（O₃）has been highlighted,the causes and sources of pollution have attracted wide attention.Volatile organic compounds（VOCs）,as important precursors to O₃ and secondary components of PM_2.5,become the hot spot of research in China.Anthropogenic VOCs in the near-surface atmosphere have a wide range of sources,and emission from the coal chemical industry is one of the important sources.The coal chemical industry is a unique phenomenon under the background of coal as the main energy structure in China,and there is no precedent in the world on how to control the air pollution caused by the coal chemical industry.The research on near-surface atmospheric compound pollution and regional ambient air quality in typical cities is still very limited.China’s coal chemical industry is increasingly concentrated in the western region with strong solar radiation.The atmospheric photochemical reaction is strong and the effect on regional ambient air quality through transmission is unclear.In this study,field observation and laboratory simulation methods were used to carry out intensive observation of VOCs in typical coal chemical cities,coal chemical parks,and key coal chemical enterprises’pollution sources（wastewater treatment）in Northwest China in the summer of 2021 and 2022.The pollution characteristics and sources of VOCs in typical coal chemical cities,coal chemical parks,and key coal chemical enterprises pollution sources（wastewater treatment）were studied,and the potential contribution of key VOCs component to the generation of O₃ and SOA was analyzed.This study provides a scientific basis for understanding the pollution and impact of VOCs in the typical coal chemical industry.The results show that:（1）The total concentration of 30 key VOCs（OVOCs）in typical coal chemical cities during the observation period was 20.76μg/m³.Acetone（12.53μg/m³）,formaldehyde（4.06μg/m³）and acetaldehyde（0.64μg/m³）were the main three OVOCs,accounting for 82.98%ofΣ30OVOCs.The largest contributor to the OH radical depletion rate(L_OH)was formaldehyde,followed by acetaldehyde and glutaraldehyde,while the three OVOCs that contributed most to the ozone generation potential（OFP）were formaldehyde,glyoxal and acetone.Based on the formaldehyde to NO₂ ratio（FNR）,it was found that the O₃-NO_X-VOCs sensitivity at a typical urban site in Changji Prefecture was transitional regime at 15:00-19:00and the rest of the day was in VOCs-limited regime.（2）The total mixing ratio of 115 VOCs was 89.32±50.57 ppbv in the coal chemical industrial park during the observed period,which was significantly higher than that detected at the urban site in the city where the coal chemical industrial park was located（26.00±12.00 ppbv）.Oxygenated VOCs（OVOCs）were the most abundant VOCs,accounting for 48.2%of the total VOCs.Ethanol,propionaldehyde and formaldehyde were the top three OVOCs species.The total ozone formation potential（OFP）of VOCs was 595.64μg/m³.The contributions of VOCs to OFP were OVOCs>alkenes>aromatics>alkanes>halogenated hydrocarbons>sulfur-containing VOC>alkyne.The top ten VOCs contributing to OFP were OVOCs,alkenes and aromatics,of which propionaldehyde contributed the most（22.2%）.The top VOCs contributing to SOA formation potential（SOAFP）were m/p-xylene,o-xylene and ethylbenzene,of which m/p-xylene contributed the most（29.6%）.Overall,OVOCs such as propionaldehyde and formaldehyde,alkenes such as cis-2-butene,and aromatics such as m/p-xylene and o-xylene contribute significantly to the complex air pollution in the coal chemical industrial park and are the VOCs species of key concern for carrying out PM_2.5 and O₃ synergistic control.（3）The VOCs monitoring of typical coal chemical enterprises shows that the VOCs concentration in the wastewater treatment area is higher than that in the atmospheric environment of the city and the park during the observation period.In the wastewater treatment area of enterprise A,the concentration of alkanes account for the highest proportion,followed by halogenated hydrocarbons;alkanes contributed the most to OFP,followed by aromatics.In the wastewater treatment area of enterprise B,the concentration of OVOCs accounts for the highest proportion;OVOCs contributed the most to OFP,followed by alkanes.The concentration of VOCs was high in the hydrolysis tank,regulating pond,neutralization sedimentation tank and flotation tank,which is related to the high content and large volatilization of organic pollutants in the wastewater treatment process.During the observation period,in the wastewater treatment areas of enterprise A and enterprise B,alkanes contributed the most to SOAFP,followed by aromatic hydrocarbons.In general,alkanes,aromatic hydrocarbons and OVOCs have important contributions to the formation of O₃ and SOA in the coal chemical wastewater treatment area.（4）From the perspective of VOCs spatial distribution at different scales in the coal chemical industry,the concentrations of VOCs were:wastewater treatment area of coal chemical enterprises>chemical industrial park>typical coal chemical cities.For VOCs components,OVOCs occupied a large proportion of city areas and industrial parks,which were the key VOCs in ambient air.The key VOC species emitted in the wastewater treatment area of the enterprise differ significantly from the ambient air,with alkanes being more prominent.OVOCs,alkenes and aromatics contribute significantly to the formation of O₃ and SOA in the coal chemical industry and should be treated as key control species in the coal chemical industry.In addition to the three species mentioned above,extra attention should be paid to the discharge of alkanes in the area of the enterprise’s wastewater treatment.