Impacts Of Volatile Organic Compound Emissions From Energy Extraction And Utiliation Processes On Atmospheric Photochemistry

Atmospheric photochemical pollution,marked by high ozone concentrations,is one of the major regional environmental problems faced by industrial and urban areas around the world.The energy extraction and utilization process will emit a large amount of ozone precursors,such as volatile organic compounds（VOCs）.China is the world’s largest primary energy consumer.In 2020,China’s primary energy consumption accounted for about 26.1%of the global total.At present,China’s control of ozone precursor emission sources mainly focuses on industrial sources and road traffic sources,and there is still a large lack of understanding of the characteristics of precursor emissions in other links.Important emission sources in other links include upstream oil extraction,midstream coal chemical industry,and end-use volatile chemical products（VCPs）.Understanding the pollution characteristics of these emission sources and their atmospheric chemical effects has practical significance and reference value for strengthening the prevention and control of ozone pollution in China.This paper studies the effects of oil extraction,coal chemical industry,and VCP use on the pollution characteristics of ozone and its precursors and atmospheric photochemical processes.The methods used in this paper are the atmospheric photochemical box model and source apportionment model,combined with comprehensive atmospheric observation data and emission inventory of representative regions or cities.This study selects the Yellow River Delta region（oilfield）and Yulin city（coal chemical industry area）as the research objects of oil extraction and coal chemical industry activities.Since the impact of VCPs emissions in the United States is currently more significant,and the emission inventory and observation data on VCPs in the United States are relatively complete,Los Angeles was selected as a representative city for the study of the photochemistry of VCPs.First,based on observation data,the effects of oil extraction and the coal chemical industry on the concentration level and pollution characteristics of ozone and its precursors（especially VOCs）were revealed.Then,various methods were used to identify the main emission sources of VOCs.The VOC emission source profiles of China’s oil extraction was calculated and obtained,and the contribution of the coal chemical industry to ambient air VOCs was quantified.Finally,the effects of oil extraction,coal chemical industry,and VCPs on ozone formation mechanisms and atmospheric oxidative capacity and free radical chemistry were quantitatively assessed using atmospheric photochemical models combined with observation data or emission inventory.Based on systematic observation data from the Yellow River Delta,the concentration levels and pollution characteristics of ozone and its precursors in China’s oil extraction areas were determined.During the observation period,the concentrations of the main primary pollutants all showed the characteristics of high in winter and spring,low in summer,high at night,and low in the daytime.The concentration of VOCs in the ambient air in this area is high,and the total concentration of non-methane hydrocarbons in winter is(71.1 77±527.177 ppb on average.The temporal variation characteristics of ozone pollution are significantly different from those of primary pollutants.Its concentration is lower in winter and spring but frequently exceeds the standard in summer（22/40;defined as the maximum hourly ozone concentration exceeding the national secondary standard for ambient air quality by 93 ppb）.There is a rapid accumulation of ozone concentration in the morning in summer,indicating a strong photochemical reaction in this area.Based on the observation data in the source area,the emission source profile of VOCs from oil production in China was calculated for the first time,revealing the important contribution of oilfield emissions to alkanes.The MCM atmospheric chemistry box model was used to quantitatively analyze the atmospheric oxidation capacity,free radical chemistry,and ozone formation mechanism around the oilfield by combining the observation data.The results show that this area has a strong atmospheric oxidizing capacity.The concentrations of main oxidants,such as hydroxyl radicals and peroxy hydroxyl radicals,are comparable to those of heavily polluted urban areas.The photolysis of oxygen-containing VOCs is the most important primary source of RO_x radicals（RO_x=OH+HO₂+RO₂）.In particular,the lower NO_x（Nitrogen O_xides）concentration and higher VOC concentrations in this region can significantly promote the chemical cycle of radicals.As a result,the concentration of OH radical peaks in the morning,thus promoting rapid ozone production.This further explains the rapid accumulation of ozone concentration during the morning hours in summer.The ozone formation analysis found that reducing NO_x emissions can effectively alleviate regional ozone and photochemical pollution in this area.Based on the observation data of Yulin city,the effects of coal chemical activities on the concentration and chemical composition of VOCs in urban ambient air and the mechanism of ozone formation were preliminarily identified.Although the population density and economic development level of Yulin are relatively low,the total concentration of VOCs in winter is comparable to or even several times higher than that of megacities such as Beijing,Shanghai,and Guangzhou（1.2-2.7）.Among the main VOC categories,the contribution of aromatic hydrocarbons,especially xylene,in Yulin city is significantly lower than that in megacities.In comparison,the contribution of naphthalene（an important byproduct of the coal chemical industry）is significantly higher,reflecting the important contribution of coal chemical activities to VOC emissions.The contribution of coal chemical emissions to the VOC concentration level was further quantified by applying a source apportionment model,which was 8.8±1.8%.Based on the OFP and VOC OH reactivity indicators,their contributions increased to 17.9 ± 6.8%and 16.9 ± 7.4%,respectively,and naphthalene was the main reactive species emitted by coal chemical activities（OFP:65.7%;VOCs OH reactivity:70.5%）.The MCM chemical box model was applied to quantitatively evaluate the impact of coal chemical emissions on local ozone formation in combination with source apportionment results.The results show that the effect of pollutant emissions from the coal chemical industry on ozone formation will be amplified due to the increase of surface albedo in a snow-covered environment.The effects of VCP emissions on urban free radical chemistry and ozone were identified using a chemical box model combined with Los Angeles observations and emission inventory.There were significant contributions to the primary source of free radicals（HO₂:28.0%;RO₂:41.2%）and the ozone concentration（MDA8 ozone:23.3%,14.1±2.9 ppb）.Adding VCP emissions can better explain the difference between the simulated and observed results of the ozone change trend in Los Angeles during 2010-2020.In recent years,the ozone formation mechanism in Los Angeles is changing,and it is gradually transitioning from the NO_x control area to the NO_x and VOCs jointly controlled area,which leads to the gradual weakening of the"weekend effect" of ozone in Los Angeles.Reducing the emission of VCPs will effectively alleviate the ozone pollution problem in Los Angeles.Further comparison of the model performance of several international mainstream atmospheric chemical mechanisms（MCM,RACM2,RACM2-VCP,SAPRC07B and CB6r2）for the atmospheric photochemical process caused by VCPs emissions shows that MCM can better reproduce the observed concentrations of ozone and its precursors.The simulation results of RACM2-VCP showed high consistency with MCM;the effects of RACM2 and SAPRC07B were similar,but the simulation effect was inferior to that of MCM;the simulation results of CB6r2 were significantly different from the observed values and the simulation results of other chemical mechanisms.In this study,a systematic study was carried out on pollutants emitted from energy extraction and processing such as oil extraction,coal chemical industry,and VCPs use.Under the background of current energy structure adjustment and increasingly prominent photochemical pollution of China,this study can provide a reference to strengthen the prevention and control of ozone pollution in China.