Source Apportionment Of Volatile Organic Compounds In Urban Areas Based On Tower Observation

Volatile organic compounds(VOCs)have many components and complex sources.Many VOC species have strong toxicity and carcinogenicity.VOCs are mainly from natural sources and man-made sources.They are important precursors of ozone(O3)and secondary organic aerosol(SOA),they also play important roles in the formation of O3 and SOA pollution.Studying the characteristics of VOC emissions in urban areas is very important to explore the formation mechanism of air pollution and their control in urban areas in China.In this study,the high-resolution proton transfer reaction time-of-flight mass spectrometer(PTR-ToF-MS)is used as an online measurement technology.The 450 m sightseeing platform of Canton tower is selected as an altitude observation station in an urban area of Guangzhou to carry out the online measurement of VOCs.The composition and concentration changes of atmospheric VOCs based on tower observation are analyzed,and the source of VOCs is analyzed.During the observation period,the highest concentration of O3 reached 136.2 ppb,and the average concentration was 32.8 ± 23.6 ppb.The Diurnal variation pattern shown a trend of high at noon and low at night.The maximum concentration of nitrogen oxides(NOX)reached 80.5 ppb,and the average concentration was 11.3 ± 7.1 ppb.The Diurnal variation of NOx shown a trend of high at night and low during the day.The maximum concentration of sulfur dioxide(SO2)reached 17.3 ppb,with an average concentration of 1.45 ± 1.1 ppb,and its daily variation are unobvious.The highest concentration of carbon dioxide(CO2)reached 601.2 ppm,with an average concentration of 430.9 ± 20.2 ppm.The concentration of total volatile organic compounds(TVOCs)was 51.8 ± 31.6 ppb.Ethanol was the most important species with the highest concentration during the field campaign,with an average concentration of 15.82 ppb.Contributions of Oxygenated volatile organic compounds(OVOCs)to TVOCs was significantly,accounting for eight species of the top ten highest species.According to the results of positive matrix factor analysis(PMF)receptor model,VOCs in urban areas of Guangzhou mainly come from five sources: daytime mixing sources,visitor-related sources,vehicle and industrial sources,long-range transport sources and volatile chemical product-related(VCP-related)sources.Average concentrations of them were 13.7 ± 11.4 ppb,16.3 ± 20.9 ppb,14.4 ± 17.8 ppb,2.6 ±1.7 ppb,and 6.7 ± 5.5 ppb,respectively.Our study shows that although the contribution of visitor-related sources is significant,it is not the main source of VOCs in the upper atmosphere of Guangzhou urban area.The VOCs of Guangzhou urban area are mainly from vehicles and industrial emissions.The ratio of toluene to benzene(T/B)also confirmed this.Motor vehicles and industrial emissions account for 22.9% of TVOCs.In addition to motor vehicle and industrial emission sources,daytime mixed sources and VCP-related sources also contribute significantly to VOCs.Since VOCs from daytime mixed sources are mainly formed through secondary generation,the contribution of VCP-related sources to VOCs in urban areas of Guangzhou are not negligible,even though VCP-related sources account for only 11.2%.The results of this study provide a good data support for in-depth understanding of the concentration level and characteristics of VOCs in urban areas.The spatio-temporal distribution of various VOCs in urban ambient atmosphere and their chemical transformation characteristics in atmosphere will help us to formulate more effective measures for the control of secondary air pollution.