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A typical particulate matter pollution process occurred from October 9 to 17,2018,in Langfang,and 99 types of volatile organic compounds (VOCs) were monitored by using ZF-KU-1007. The characteristics of VOCs,formation potential of secondary organic aerosol (SOA),and source of VOCs were systematically analyzed. The results showed that the maximum concentration of PM 2.5 was 198 μg·m -3 during the pollution process and was 2.64 times the National Ambient Air Quality Standard (GB 3095-2012). The average concentration of VOCs was 56.8×10 -9 ,127.8×10 -9 ,and 72.5×10 -9 in the early,middle,and late stages of the pollution process,respectively,and the concentration of VOCs increased significantly in the middle stage. The formation potential of SOA was significantly positively correlated with PM 2.5 ,and the contribution of aromatic hydrocarbon for SOA was larger and significantly correlated with the concentration of PM 2.5 . In the middle pollution stage,SOA increased,and the contribution ratio of aromatic hydrocarbon increased significantly. Conversely,the contribution of alkanes and olefin decreased significantly,which showed that aromatic hydrocarbons,namely benzene series,were the dominant species of SOA generation and had a great influence on the pollution process. Benzene,toluene, m -/ p -xylene, o -xylene,and ethylbenzene and nonane,n-undecane,and methylcyclohexane were the priority control species in this pollution process. Solvent use source and motor vehicle emission source (gasoline and diesel vehicles) were the main sources affecting the concentration of VOCs during the autumn pollution process of Langfang,among which the contribution of gasoline vehicle emissions increased significantly in the middle pollution contribution and was the key control source.

Continuous sampling using the tank sampling method were conducted in Changsha, Zhuzhou, and Xiangtan cities from August 18 to 27, 2020, and 106 VOCs species were analyzed using GC-MS analysis. Then, the regional VOCs concentrations, generation potential, and source of VOCs were studied. The results showed that the average φ (VOCs) was (20.5±10.5)×10 -9 in the Changsha-Zhuzhou-Xiangtan area, in which OVOCs (33.5%) and alkanes (28.2%) accounted for the highest proportion. The ozone formation potential (OFP) of VOCs was 118.5 μg·m -3 , and the contributions of aromatic hydrocarbons, olefin, and OVOCs to OFP were 37.4%, 24.2%, and 23.6%, respectively. The average secondary organic aerosol formation potential (SOA p ) of the VOCs was 0.5 μg·m -3 , and the contribution of aromatic hydrocarbons to SOA p was 97.0%, among which C8 aromatic hydrocarbons contributed 41.7%. Toluene, m/p -xylene, and o -xylene were the common dominant species that contributed significantly to OFP and SOA p . The characteristic ratio results showed that VOCs in Changsha were relatively influenced by industrial processes and solvent use, whereas Zhuzhou and Xiangtan were more affected by coal and biomass combustion. The PMF results showed that the VOCs mainly came from vehicle exhaust and oil and gas volatilization (27.2%), coal and biomass combustion (23.7%), industrial processes (20.4%), solvent use (17.2%), and natural sources (11.5%) in the Changsha-Zhuzhou-Xiangtan area.

A total of 99 volatile organic compound(VOC) species were detected the Langfang development zones based on continuous monitoring using a ZF-PKU-1007 between August 25 and September 30, 2018. The concentrations, reactivity, and sources of VOCs were studied under different O 3 concentrations using compositional analysis. The results showed that the average VOCs concentration during the research period was(75.17±38.67)×10 -9 , and was(112.33±30.96)×10 -9 , (66.25±34.84)×10 -9 on pollution days and cleaning days, respectively(VOCs concentrations were 69.6% higher on pollution days). The contribution of VOCs species to the ozone formation potential(OFP) were ranked in the order aldehydes > aromatics > alkenes > alkanes. In the case of L ·OH , the main contributions were from aromatics(30.0%) and alkenes(25.8%) on pollution days, while the contribution from aromatic alkenes(29.8%) was a slightly higher than aromatics(28.0%) on cleaning days. By applying the positive matrix factorization(PMF) model, five major VOCs sources were extracted, namely vehicle emissions(34.4%), solvent usage and evaporation(31.7%), the petrochemical industry(15.7%), combustion(11.1%), and plant emissions(7.9%). The contributions of solvent usage and evaporation and plant emission sources on pollution days were 13.1% and 1.2% higher than on cleaning days, respectively, which was likely due to relatively higher temperatures on these days. Therefore, vehicle emissions and solvent usage and evaporation should be priorities in VOCs control strategies for the Langfang development zones between August to September.

Heavy pollution events frequently occur during fall and winter seasons in northern areas. In order to understand the characteristics and chemical composition of PM 2.5 during heavy pollution in winter in Liaocheng City, ambient PM 2.5 samples were collected between January 7-11,2016. Mass concentration, water-soluble ions, carbonaceous species, and elements were analyzed, as well as the causes of pollution. Results showed that PM 2.5 mass concentration was 238.3 μg·m -3 with the trend clearly that of an inverted V; this concentration represents exceedance of the National Ambient Air Quality Standard (GB 3095-2012) by more than 2.2 times. NO 3 - , SO 4 2- , and NH 4 + (SNA)were the main water-soluble ions. As pollution increased or decreased, NH 4 + , SO 4 2- , NO 3 - , and Cl - exhibited the same trend, which contrasted with that of Ca 2+ . During the peak of pollution, NH 4 + , NO 3 - , and SO 4 2- concentrations were 48.96, 68.45, and 80.55 μg·m -3 , with these representing levels 6.29, 7.31, and 7.84 times those of the initial stage, respectively. During the pollution event, OC and EC concentration variation ranges were 20.8-60.2 μg·m -3 , and 3.0-7.5 μg·m -3 , respectively. The concentration of OC was significantly higher than that of EC and the variation amplitude was significantly larger. During the event, the mass concentrations of 27 inorganic elements on each day were 10.2, 22.4, 16.0, 19.6, and 8.2 μg·m -3 , respectively. Enrichment factors (EF) of all elements were less than 10, indicating lack of enrichment and showing that sources were mainly natural. PM 2.5 mass concentration reconstruction results showed that organic matter (OM), SO 4 2- , and NO 3 - were major components, followed by NH 4 + , crustal material, and other ions. EC and trace element content was relatively low. As PM 2.5 pollution worsened, secondary inorganic salt (NH 4 + , SO 4 2- , NO 3 - ) concentrations and proportions increased, OM concentration increased but its proportion decreased, while crustal material concentration and proportion both decreased, showing that secondary inorganic conversion was the main cause of this pollution event, mainly driven by coal and motor vehicle emissions.