VOCs source analysis and secondary organic aerosol contribution during haze pollution in Xi'an City
The characteristics,aging degree and diurnal variation of VOCs in two haze pollution processes(pollution process Ⅰ:from December 29,2022 to January 6,2023;Pollution Process Ⅱ:from January 7,2023 to January 13,2023)were analyzed,based on the continuous on-line observation da-ta of haze pollution period at the Xi'an Super Station(December 29,2022-January 13,2023).The sources of VOCs during haze pollution episode were analyzed by characteristic ratio method and or-thogonal matrix factorization(PMF).The formation potential of secondary organic aerosols(SOA)was estimated by the method of aerosol formation coefficient(FAC).Result showed that the volume con-centration of VOCs were(113.10±29.46)×10-9,and(95.23±21.40)×10-9in heavy pollution process Ⅰ and Ⅱ.The proportion of organic compounds and alkanes was more than 70％ .Compared to the situ-ation in the clean days,aromatic hydrocarbons showed the largest increase,Oxygenated Organic Compounds(OOCs)showed the largest increase in value,and acetylenic hydrocarbons showed a de-crease indicating a significant cumulative effect of severe aging of the air mass.In Process Ⅱ alkanes de-clined,reflecting the significant emission reduction effect of activating the heavy weather warning.The di-urnal variation was high at night and low at day,with a small peak at about 09:00.The analysis of char-acteristic ratio shows that benzene and toluene in VOCs come from the source of solvent,the source ap-portionment results of PMF model showed that VOCs mainly came from vehicle exhaust(20.54％ ),ex-ternal imported sources(19.02％ ),food sources(13.99％ ),industrial solvent sources(10.72％ ),and industrial production sources(35.72％ ).By estimating the SOA generation potential,it was concluded that the benzene series compounds(BTEX)and naphthalene in aromatic hydrocarbons were the main substances of SOA pollution.
heavy pollution episodevolatile organic compounds(VOCs)characteristic ratio meth-odsource resolutionsecondary organic aerosol(SOA)
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