The most important emissions of natural sources are isoprene and monoterpene; transportation is the world's largest source of anthropogenic VOCs, and solvent use is the second largest source of emissions; through trunk road research, tunnel research, laboratory drums and The bench experimental study has mastered the composition characteristics of VOCs in different vehicle exhausts. The main sources of VOCs using CMB and PMF models are motor vehicle exhaust, fuel volatilization (LPG, NG and gasoline), petrochemicals and coatings/solvents. Use, etc., to provide reference for further research on VOCs source analysis.

Based on the domestic and international research on the emission of volatile organic compounds (VOCs) in the atmosphere, the research status of VOCs emission sources and source analysis in ambient air is described. The results show that the most important emissions of natural sources are isoprene and monoterpene; transportation is the world's largest source of VOCs anthropogenic emissions, solvent use is the second largest source of emissions; through traffic trunk research, tunnel research, experiments The experimental research on the chamber drum and the gantry has mastered the composition characteristics of VOCs of different vehicle exhausts. The main sources of VOCs using CMB and PMF models are motor vehicle exhaust, fuel volatilization (LPG, NG and gasoline), petrochemicals and The use of coatings/solvents provides a reference for further research on VOCs source analysis.

1 Introduction

Volatile organic compounds (VOCs) are a class of organic pollutants that are ubiquitous in air and have complex composition. The pollution is mainly manifested in two aspects. On the one hand, most VOCs have toxicological properties and endanger human health; On the one hand, some VOCs have strong photochemical reactivity and can undergo secondary transformation in the environment. Its photochemical reaction dominates the process of photochemical smog, which is critical for the generation of urban and regional ozone [1] and is one of the important precursors for ash weather [2, 3]. In short, volatile organic compounds (VOCs) play an important role in promoting the formation of complex air pollution.

The first comprehensive plan for air pollution prevention and control issued by the Ministry of Environmental Protection of China - "Twelfth Five-Year Plan for Prevention and Control of Air Pollution in Key Areas" clearly states that volatile organic compounds (VOCs) are one of the key pollutants for air pollution control in the next stage. It can be seen that the problem of VOCs pollution has caused great concern in China. Mastering the main emission sources of VOCs and their emission characteristics is the basic premise for controlling VOCs pollution. To this end, based on the research status quo at home and abroad, this paper discusses the research status of VOCs emission sources and VOCs in ambient air, and provides a scientific basis for VOCs pollution control.

2 Study on emission sources of VOCs in ambient air

The sources of VOCs are mainly human and natural sources. On a global scale, natural sources contribute more to VOCs than anthropogenic sources. Natural sources include plant release, volcanic eruptions, forest grassland fires, etc. The most important sources of emissions are forests and shrubs. The most important emissions are isoprene and monoterpenes.

Anthropogenic sources can be divided into fixed sources, mobile sources and unorganized emission sources. The fixed sources include fossil fuel combustion, the use of solvents (paints, paints), waste combustion, petroleum storage and transportation, and petrochemical and steel industries. Emissions from metal smelting; sources of emissions include emissions from vehicles such as motor vehicles, aircraft and ships, and emissions from non-road sources; unorganized sources include biomass burning and solvent volatilization of gasoline and paint. Transportation is the world's largest source of anthropogenic VOCs, and solvent use is the second largest source of emissions. At present, the research on natural and anthropogenic sources of VOCs is widely studied at home and abroad.

2.1 Natural source research of VOCs

Plant sources are the most important source of natural sources of VOCs. Domestic and foreign research mainly includes plant VOCs emission rate, emission estimation and VOCs emission characteristics of different types of vegetation. Ignacio et al. [4] studied the emission rates of two species of VOCs in Mexico and their effects on the environment. The study found that the rates of poplar and sylvestre areoprene and monoterpenes were higher, but poplars The emission rate of formic acid, acetic acid, formaldehyde and acetaldehyde is higher than that of western yellow pine, and the total emission is four times that of western yellow pine. Jeanie et al. [5] tested the isoprene emission rate and the estimation of plant-derived VOCs emissions from 13 species in Hong Kong's wild suburbs. The results showed that the total emission of plant-derived VOCs in Hong Kong was 86×109gC, among which The contributions of pentadiene and monoterpene were 30% and 40%, respectively. Xie Yangxuan et al [6] established a list of VOCs emissions from natural sources of garden green space in Beijing, and concluded that the annual total emissions (in C) of Beijing garden green space VOCs is about 385×104t, of which isoprene 309×104t, single Terpenes 059 × 104t, other VOCs 016 × 104t; and emissions have obvious seasonal dependence, of which the maximum summer emissions are 249 × 104t, accounting for 647,% of the year, and at least 00086 × 104t in winter, accounting for 02% of the year. The total emission of natural source VOCs in the Pearl River Delta region is 296 × 104t, of which isoprene 730 × 104t, accounting for 247%, monoterpene 102 × 104t, accounting for 344%; and emissions are typical of summer high winter low Characteristics include 405% in summer and 111% in winter. Natural VOCs emissions are mainly concentrated in areas with low urbanization and dense forest areas [7, 8]. It can be seen that the most important emissions of natural sources are isoprene and monoterpenes. Subsequently, He et al. [9] established a list of emissions of isoprene and monoterpenes from many species in the Xilin River Basin of Inner Mongolia; Hai et al. [10] measured the emission rates and emission inventories of 10 VOCs in Japan.

2.2 Anthropogenic Sources of VOCs

At present, transportation is the largest anthropogenic emission source of VOCs in the world. The research on mobile vehicles is more extensive, mainly including traffic trunk research, tunnel research, laboratory drum and bench experimental research.

The research on traffic trunk VOCs mainly discusses the species composition characteristics of atmospheric VOCs on both sides of urban traffic trunks and intersections, and analyzes the influence of vehicle exhaust on atmospheric VOCs. The United States [11,12], Japan [13], Ireland [14], Hong Kong [15], Beijing [16], Shanghai [17], Guangzhou [18], Nanjing [19] and other countries and regions are all on the main road VOCs Were studied. Olson et al. [12] studied the composition of VOCs around a highway in the United States. The study found that the concentration of VOCs around the highway is twice that of the highway. The main species are ethylene, propane, ethane, isopentane, and toluene. And n-butane. Hiroto et al [13] found that the top ten species of atmospheric VOCs on the sides of the main roads in Kanagawa Prefecture, Japan are toluene, ethane, propane, isopentane, n-butane, acetylene, isobutane, isobutylene, 3-methyl Pentane and benzene. Lu Sihua et al. [16] studied the emission characteristics of VOCs in Beijing traffic intersections, and found that the VOCs emitted by Beijing motor vehicles are mainly composed of propane, isopentane, 1-butene, benzene, toluene and xylene. And with the use of unleaded gasoline, the content of aromatic hydrocarbons has increased to a large extent. Wang et al. [19] showed that the main species of atmospheric VOCs in Nanjing trunk roads are benzene, toluene, ethylbenzene, xylene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene and carbon tetrachloride. , trichloroethylene and tetrachloroethane, and the height of 15m is significantly affected by the influence of motor vehicles, and the concentration of VOCs is the highest.

In order to grasp the emission characteristics of VOCs in motor vehicles, Paris [20], Sydney [21], Seoul [22] and Hong Kong [23], Taiwan [24, 25] and Guangzhou [26, 27] have obtained tunnel test methods. The emission level and composition characteristics of VOCs during actual driving of a motor vehicle. Touaty et al. [20] conducted field measurements and model estimation of atmospheric VOCs in a tunnel in Paris, pointing out that isopentane and ethylene are the most abundant VOCs, accounting for 25% and 214% of the TVOC mass concentration, respectively; followed by acetylene and propylene. And n-butane, which account for 10% of the TVOC mass concentration, respectively. Bronwyn et al. [21] measured the composition of VOCs in the Sydney Subsea Tunnel. The main species are C2-C5 alkanes, ethylene, propylene, acetylene, benzene, toluene, xylene, etc., of which aromatic hydrocarbons have a larger proportion; The concentration of alkanes in the VOCs of tunnel atmosphere is the highest, especially n-butane [22]. The main emission factors in atmospheric VOCs of a highway tunnel in Taiwan are isopentane, toluene, n-pentane, isoprene, 2,3-dimethylbutane, acetone, 2-methylpentane, 1-hexine. Alkene, 1,2,4-trimethylbenzene, 1-butene and propylene [25]; and the three concentrations of VOCs in Guangzhou Pearl River Tunnel are ethylene, isopentane and toluene [26,27]. The test results of tunnel experiments are related to the influence factors of local motor vehicle composition, traffic conditions, meteorological conditions, etc., and it is impossible to accurately distinguish the emission characteristics of VOCs of various types of vehicles. To this end, the VOCs emission test of various models was carried out at home and abroad using laboratory drums and bench test methods. Schauer et al. [28,29] used the laboratory drum method to study the emission factors of medium-duty diesel trucks and gasoline vehicle exhausts. The higher concentrations of VOCs were acetone, ethylene, acetylene, toluene, propane, benzene and toluene. Xylene, benzene, C2-C4 alkanes and alkenes. Tsai et al. [30] used the bench test method to compare and analyze the species composition of VOCs in motorcycle exhausts of four types of vehicles under different driving conditions, mainly including alkanes and aromatic hydrocarbons, followed by isopentane, n-pentane and gly. Alkane and benzene, toluene, xylene, and the concentration of VOCs emission factors under different working conditions are decelerating > uniform speed > acceleration. Qiao Yuezhen et al [31] obtained the source composition spectrum of vehicle exhaust VOCs in various models of Shanghai by chassis dynamometer and actual road test method. The light gasoline vehicle exhaust VOCs are mainly aromatic hydrocarbons such as toluene and xylene; heavy diesel vehicles are propane. The alkane components such as n-dodecane and n-undecane are mainly composed of oxygen-containing components such as acetone; the main component of motorcycles and LPG mopeds is acetylene.

T/B (toluene/benzene) is commonly used to evaluate the contribution of vehicle exhaust to ambient air [32]. It is generally considered that T/B less than 20 indicates significant impact on vehicle exhaust emissions [33]. The smaller the impact of the motor car, the greater the impact of other VOCs such as solvent volatilization. Chen Changhong [34] found that the average value of T/B in urban areas of Shanghai was 351, indicating that the urban atmosphere in Shanghai was affected by the emission of other VOCs such as solvent volatilization.

The use of solvents is the second largest source of emissions for VOCs. Fauser et al. [35] found that Danish solvent-derived NMVOC accounts for 1/3 of total emissions. Yuan et al. [36] studied the composition of VOCs in the coatings and printing industries. The results showed that toluene and C8 aromatic hydrocarbons are the most abundant species in coating VOCs. Long-chain alkanes and aromatic hydrocarbons are the highest in printed VOCs. Species. John et al. [37] found that acetaldehyde and hexanal released from alkyd paints can seriously harm human health. At present, there are few studies on VOCs produced by volatilization of solvents and coatings at home and abroad, and the composition characteristics of VOCs volatilized by different kinds of solvents are still unclear.

3 Source analysis of VOCs in ambient air

The study of the sources of VOCs in the ambient air, the emissions of pollution sources, and the contribution to ambient air are fundamental studies for controlling atmospheric VOCs. After sampling and analysis, VOCs often use the receptor model to determine the main pollution sources and the relative contribution of each pollution source to atmospheric VOCs pollution. The US National Environmental Protection Agency (EPA) recommended PMF model and chemical mass balance receptor (CMB) model are applications. The most extensive source resolution technology.

The source analysis of foreign atmospheric VOCs started earlier. Since the 1970s, the US EPA has issued the CMB10 version of the application software, and the source analysis research has made great progress. Vega and Na[38-39] used the CMB receptor model to analyze the atmospheric VOCs in Mexico and Seoul, respectively, and found that the atmospheric VOCs in Mexico mainly originated from the use and leakage of motor vehicle exhaust gas and liquefied petroleum gas (LPG). , accounting for 587% and 242% respectively; while the relative contributions of motor vehicle exhaust, solvent use, oil and gas volatilization, liquefied petroleum gas (LPG) and natural gas (NG) in Seoul, Korea were 52%, 26%, 15%, 5% and 2%.

China's source analysis research started late, and related research on source analysis began in the late 1980s, but it also achieved certain results. In recent years, the source analysis of atmospheric VOCs has applied more PMF models, mainly in Beijing, Shanghai, and the Pearl River Delta. Lu Sihua and Song [40-41] analyzed the anthropogenic sources of atmospheric VOCs in Beijing. Lu Sihua's research found that motor vehicle exhaust 62%, oil and gas volatilization 9%, liquefied petroleum gas 10%, paint 6%, petrochemical industry 6%, unknown source 6%; Song's research found that motor vehicle exhaust, oil and gas volatilization, petrochemical, LPG, natural gas, paint and paint, diesel vehicles and biomass emissions, the contribution rate is 52%, 20%, 11% , 5%, 5%, 3%, 2%. It can be seen that the sources of atmospheric VOCs in the same region are different at different time periods, but the main source is still motor vehicle exhaust.

Cai et al [42] found that the sources of atmospheric VOCs in Shanghai urban areas are mainly motor vehicle exhaust, chemical industry, solvent evaporation, solvent use, steel industry, biomass burning and coal combustion, and their contribution rates are 25% and 17%, respectively. , 15%, 15%, 12%, 9%, 7%. At the same time, Cai Changjie, Wang Qian and others [43,44] conducted an analysis of atmospheric VOCs in summer and autumn in Shanghai, respectively. It is concluded that the main sources of summer VOCs are motor vehicle exhaust emissions of 34% and fuel volatilization (LPG, NG and Gasoline volatilization) 24%, solvent use 16%, industrial production and biomass burning 14%, marine source 12%; and autumn Shanghai atmospheric VOCs are mainly from automobile exhaust 24%, incomplete combustion 17%, fuel volatilization 16% LPG/NG leaks 15%, petrochemical 14%, and paint/solvent use 13%. It can be seen that the main sources of atmospheric VOCs in Shanghai and Beijing are motor vehicle exhaust, but the contribution rate of Shanghai is lower than that of Beijing.

Guo et al [45] used the PMF model to find that the main sources of pollution in Hong Kong and the Pearl River Delta are motor vehicle exhaust, solvent use and biomass burning. The largest contribution rate in Hong Kong is motor vehicle exhaust (48). ±4%), followed by the use of solvent (43 ± 2%); while in the Pearl River Delta