Compilation of emission inventory and source profile database for volatile organic compounds: A case study for Sichuan, China

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Compilation of emission inventory and source profile database for volatile organic compounds: A case study for Sichuan, China Zihang Zhou∗, Qinwen Tan, Ye Deng, Danlin Song, Keying Wu, Xiaoling Zhou, Fengxia Huang, Wenhao Zeng, Chengwei Lu Chengdu Key Laboratory of Air Pollution Research, Chengdu Academy of Environmental Sciences, Chengdu, 610072, China

ARTICLE INFO

ABSTRACT

Keywords: Volatile organic compounds (VOCs) Oxygenated organic compounds (OVOCs) Sichuan basin Source profile Speciated VOCs emission inventory Ozone formation potential (OFP)

The purpose of this paper is to develop an emission inventory and source profile database for volatile organic compounds (VOCs) in Sichuan Province. Based on the test data of the research literatures, the source profiles of species containing no oxygenated volatile organic compounds (OVOCs) were revised and reconstructed to obtain the normalized VOCs source profile. In addition, the source profile-based 1 km × 1 km speciated VOCs emission inventory was established in accordance with the 2015 Air Pollution Source Emission Inventory in Sichuan Province with the ozone formation potential (OFP) estimated to assess the impact on ozone formation. There were 45 profiles and 519 species included in the established VOCs source profile database. Since the profiles were established mainly based on domestic test data, foreign research results were employed to supplement the profiles of some sources that had not been actually tested or had been researched less in China. In addition, the profiles of some sources such as biomass burning and transportation with emissions containing rich OVOCS have been revised and reconstructed, and the profiles including redundant data of many tested sources were simplified accordingly as well. Therefore, the established source profile database is well applicable to the establishment of the speciated VOCs emission inventory and the source apportionment. The VOCs emission inventory showed that the anthropogenic emissions of alkanes, alkenes, alkynes, aromatics, OVOCs, halohydrocarbons and other VOCs in Sichuan Province were 167.1 kt, 77.4 kt, 13.2 kt, 216.7 kt, 202.7 kt, 32.5 kt and 64.2 kt respectively; the total OFP in Sichuan was 2584.9 kt, and the above-mentioned VOCs contributed 6.9%, 26.1%, 0.5%, 42.3%, 23.2%, 0.4% and 0.5% to the total OFP, respectively. Therefore, alkenes, aromatics and OVOCs were the major species for ozone formation among the VOCs emitted in Sichuan Province, and controlling the emissions of such species plays a key role in reducing ozone formation. The major VOCs species emitted in various cities of Sichuan Province were aromatics, OVOCs and alkanes; however, different cities have their own remarkable characteristics. VOCs emissions and major OFP contributing species in Sichuan Province were mainly distributed in the Sichuan Basin as well as some areas in Liangshan and Panzhihua, where the population was relatively dense and the industry was relatively developed. The main source of m-Xylene and toluene was solvent use; therefore, m-Xylene and toluene were more intensively distributed in urban built-up areas. Furthermore, since biomass burning contributed a lot to ethene and formaldehyde emissions, ethene and formaldehyde were substantially distributed in cultivated areas in eastern Sichuan and southern Sichuan.

1. Introduction Volatile organic compounds (VOCs) generally include C2–C12 nonmethane hydrocarbons, C10–C20 high carbon hydrocarbons, oxygenated volatile organic compounds (OVOCs), halohydrocarbons and other organic matters (Watson et al., 2001). They are mainly generated by natural sources and anthropogenic sources (Guenther et al., 2012; Piccot et al., 1992; Van der Werf et al., 2010). Although natural sources

are the main sources of these VOCs in the global perspective (Guenther et al., 1995; Muller, 1992), contributions of anthropogenic emissions in economically developed regions and cities have grown significantly due to the increase of human activities (Zhao et al., 2017; Kliger et al., 2002; Zhang et al., 2009). Different VOCs species have different effects on the formation of near-surface O3 and secondary organic aerosol (SOA) (Atkinson, 2000; Derwent et al., 2010; Pandis et al., 1992), and a large number of research results have shown that the formation of near-

Peer review under responsibility of Turkish National Committee for Air Pollution Research and Control. ∗ Corresponding author. E-mail address: [email protected] (Z. Zhou). https://doi.org/10.1016/j.apr.2019.09.020 Received 30 June 2019; Received in revised form 28 September 2019; Accepted 28 September 2019 1309-1042/ © 2019 Turkish National Committee for Air Pollution Research and Control. Production and hosting by Elsevier B.V.

Please cite this article as: Zihang Zhou, et al., Atmospheric Pollution Research, https://doi.org/10.1016/j.apr.2019.09.020

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surface O3 in most parts of China was mainly influenced by VOCs (Shao et al., 2009; Tang et al., 2012; Xue et al., 2014); in addition, VOCs had greatly contributed to the formation of SOA, which accounted for a large proportion in PM2.5 in China's economically developed regions (Chan et al., 2017; Ming et al., 2017; Huang et al., 2014). The high uncertainty of the speciated VOCs emission inventory of anthropogenic sources increased the difficulty in understanding the forming mechanism of secondary pollutants from the perspective of emission inventory, and interfered the determination of corresponding measures required by the VOCs/NOx optimal control ratio. China has carried out plenty of work for compiling air pollutant source emission inventories mainly in Beijing-Tianjin-Hebei, Yangtze River Delta, Pearl River Delta and other developed regions (Qi et al., 2017; Zhao et al., 2017; Fang et al., 2017), but there were few research projects conducted on speciated VOCs emission inventory (Bo et al., 2008; Wei et al., 2011); however, the receptor model and the chemical transport model require detailed VOCs species information and emissions as the model input data. The pollution source profile is the mass fraction of each VOC species relative to the total emission, which is a necessary condition for breaking down the total VOCs emission into emissions of various VOCs species (Mo et al., 2016; Watson et al., 2001). Since the 1980s, plenty of VOCs source profile research projects have been carried out in countries and regions of Europe and the United States (Wadden et al., 1986; Scheff and Wadden, 1993; Fujita et al., 1995; Doskey et al., 1999). The US EPA began to collect the data of American and Canadian VOCs source profile research projects and established the SPECIATE database, which has now been updated to Version 4.5 (Hsu et al., 2016). After years of updating and adjustment, the database has become the most comprehensive database now with the latest version including 2175 VOCs profiles, 2602 chemical species, and 34 VOCs emission sources. A similar source profile database has been developed in Europe as well (Theloke and Friedrich, 2007; Laurent and Hauschild, 2014). Since the beginning of the 21st century, the source profile testing has been drawing more and more attention, and some research teams have carried out a good deal of sample collection and analysis work, mainly focusing on fossil fuel combustion (Tsai et al., 2003; Shi et al., 2014), industrial process (Tsai et al., 2008; Wei et al., 2014), solvent use (Wei et al., 2014; Yuan et al., 2010), motor vehicles (Wang et al., 2013a; Yao et al., 2015) and other pollution sources (Zhang et al., 2013a; Zhang and Ma, 2011). Although a lot of research projects had been conducted on VOCs profiles, there were still four problems when the research results were applied to the compiling of the speciated VOCs emission inventory. Firstly, species involved in these research results varied greatly, so these research results were not quite suitable for comparation. Previous research findings showed that VOCs emitted by biomass burning and diesel vehicles contained relatively more OVOCs, and the OVOCs in the VOCs emitted by diesel vehicles even accounted for up to 20–70% (Andreae and Merlet, 2001; Zheng et al., 2013); however, this was generally neglected in the above-mentioned domestic research projects. Secondly, China's industrial pollution sources were relatively complex involving many industrial sectors. The subjects of existing testing and research projects were limited in some typical industrial sectors and process procedures, which resulted in the lack of corresponding domestic testing data of many industrial sectors. Thirdly, when a single source profile was matched to the corresponding emission source, the accuracy of emission source calculation might be reduced due to the limitation of the source profile (Reff et al., 2009). For example, since burning involved a variety of fuels and burning technology types, a single source profile was not enough to represent all the emission characteristics of burning. Finally, it is difficult to quantify the data quality of the profile of the same type of pollution sources, and the selection of source profile may lead to unpredictable uncertainty upon the application of the source profile (Li et al., 2014); therefore, it is necessary to summarize the existing Chinese research results and establish a relatively complete and systematic VOCs source profile

database for VOCs species emission calculation and source apportionment (Li et al., 2014). With the rapid economic development of the Sichuan Basin, frequent complex air pollution events such as photochemical smog and haze have become the primary environmental problems in Sichuan Province (Ning et al., 2018; Zhao et al., 2018). After a series of measures for controlling the coal combustion of power plants, industries and domestic living were taken to reduce the emissions of the primary particulate matter and the secondary particulate precursor (NOx and SO2), O3 pollution becomes the primary issue of air quality improvement as the concentration of PM2.5 in the ambient air gradually decreases. Therefore, the in-depth understanding and control of VOCs emissions are urgently required now. In order to minimize the uncertainty caused by the above problems in the establishment of speciated VOCs emission inventory, this paper took Sichuan Province as an example, made necessary adjustment and reconstruction for the collected profiles, and established the source profile database and the high-resolution speciated VOCs emission inventory of anthropogenic sources, so that they might be applied to complex air pollution research projects as well as the identification, control and other specific management of VOCs species (especially active VOCs species). 2. Materials and methodology The calculation of the speciated VOCs emission inventory was mainly conducted by multiplying VOCs emissions by the source profile of the corresponding pollution source. The method flow is shown in Fig. 1. In this paper, the VOCs emission data in the 2015 Air Pollution Source Emission Inventory in Sichuan Province (Zhou et al., 2018) were employed with VOCs profiles obtained mainly through literature research and pollution sources classified into 10 categories; the profiles not containing OVOCs were reconstructed to obtain the normalized VOCs profiles. Based on the 2015 Air Pollution Source Emission Inventory in Sichuan Province, a VOCs source profile-based speciated VOCs emission inventory was established, and the OFPs were estimated to evaluate the impact on ozone formation, so that the 1 km × 1 km gridded distribution of speciated VOCs emission inventory might be completed based on different spatial distribution parameters. 2.1. Domain of the research Sichuan Province is located in the southwest of mainland China with 21 prefecture-level cities under its jurisdiction. The research domain is 97.35°E from the west, 108.52°E from the east, 26.05°N from the south and 34.32°N from the north. This research divided the research domain into 573,225 1 km × 1 km grids, and Fig. 2 shows the domain of the research. As a large inland province in southwest China, Sichuan Province covers an area of approximately 486,000 km2, accounting for 5% of the total area of China. In 2015, its GDP was 3.01 trillion yuan. The energy consumption of Sichuan Province was about 177 million tons of standard coal with the main energy sources of coal, electricity, and natural gas accounting for 38%, 14%, and 14% respectively. 2.2. Anthropogenic VOCs emission inventory in Sichuan Province Anthropogenic VOCs emission sources including industry, transportation, domestic living, oil and gas storage and transportation and waste disposal were identified based on the technical guide for the compilation of emission inventory of atmospheric VOCs (Ministry of Environmental Protection of China, 2014). Therefore, the emission sources were divided into eight categories: fossil fuel burning, industrial process, transportation, solvent use, biomass burning, gas storage and transportation, waste disposal, and cooking. Please notice the existing research (Zhou et al., 2018) for details on the activity data and emission factors of the VOCs emission calculation 2

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Fig. 1. Technical route.

part in the air pollution source emission inventory of Sichuan Province. The 1 km × 1 km gridded emission inventory of anthropogenic air pollutants was compiled based on the research in the “bottom-up” emission inventory construction method.

dilution channel sampling method with 107 C2–C12 VOCs species obtained; Liu et al. (2008) collected VOCs samples from industrial coal burning stacks and civil coal burning stacks, and established the VOCs source profile for industrial coal burning and civil coal burning, which contains 92 types of VOCs; Tsai et al. (2003) performed the source profile test for civil boilers and furnaces fueled with coal, liquefied petroleum gas, coal gas and natural gas, and established the VOCs source profile database containing 54 VOCs species based on the fuel consumption in rural areas; Wang et al. (2013b) simulated the operation of stoves used in rural areas, which are fueled with coal from 5 different producing areas, tested the emissions, and obtained the emission characteristics of NMHCs and OVOCs. In addition, profiles of Wei et al. (2008) and SPECIATE were taken as a complement to the profiles of power generation and industrial manufacturing. Industrial process involves iron and steel industry, cement industry, chemical industry, petrochemical industry and other industrial sectors, and the corresponding VOCs emission procedures and characteristics are quite different. At present, domestic research projects mainly focus on typical pollution sources such as petrochemical industry and steel manufacturing, but source profile research projects on chemical industry and other industries with intensive VOCs emissions are extremely limited. The source profile work collected in this research mainly includes: Liu et al. (2008) collected VOCs ambient air samples from vacuum distillation and catalytic cracking installations in the refining and chemical industrial areas of petrochemical enterprises in Guangdong Province respectively to characterize the profiles of the

2.3. Compilation of the VOCs source profile database 2.3.1. Sources of profiles The profiles were selected mainly in accordance with the following three steps: first, collect the localized test results. Since the test data of Sichuan Province were limited with poor representativeness, this research was conducted mainly based on domestic test data. Secondly, make supplement with foreign test data of the pollution sources with insufficient test samples or lacking of OVOCs species information. Finally, use the SPECIATE database v.4.5 (Hsu et al., 2016) to supplement the VOCs sources not covered in the existing research results. Due to unfavorable factors of some reported research results, such as there was no test information, the test information was ambiguous or the tested species were limited, a source profile with available data, sufficient and reasonable test conditions and method, as well as representative test species was obtained based on the foregoing steps. The VOCs source profile of each pollution source is described below. The number of tests for fossil fuel burning profiles conducted in China is limited, and those collected in this paper mainly include: Shi et al. (2015) tested the VOCs samples taken from stacks of power plants, thermal power stations and other industrial processes through the

Fig. 2. Research domain in Sichuan Province. 3

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petrochemical industry. In addition, Liu et al. (2008) completed similar work in Beijing as well; Tsai et al. (2008) conducted tests on procedures of coking, sintering, thermal forming and cold forming of steel manufacturing enterprises in Taiwan; Shi et al. (2015) also carried out similar tests for steel manufacturing enterprises in Liaoning Province; however, Shi et al. (2015) adopted the dilution channel method to collect samples and established the source profile of the steel industry; Hsu et al. (2007) tested the process emissions of chemical products such as acrylonitrilebutadiene-styrene polymer and polystyrene in chemical plants of Taiwan Province and established the VOCs source profile for some chemical products. In addition, other research projects have established profiles for processes such as coatings and polyurethanes (Zheng et al., 2013; Wang et al., 2009a). Due to the lack of domestic research projects, the SPECIATE source profile was collected as a supplement. Transportation includes on-road mobile sources such as motor vehicles and non-road mobile sources such as agricultural vehicles. Considering that domestic research projects mainly focused on the onroad mobile source, gasoline vehicles and diesel vehicles were analyzed separately in the source profile of this research; however, typical nonroad mobile sources, such as construction machinery were not included due to limited research projects. Lu et al. (2003) took the lead to carry out research projects on VOCs profiles of motor vehicles in China, and initially established a source profile of motor vehicles including 60 hydrocarbons (NMHCs). Liu et al. (2008), Gao et al. (2012), Wang et al. (2013a), and Qiao et al. (2012) analyzed NMHCs species of motor vehicle VOCs based on the canister sampling and GC/MS analysis method, and established the source profiles of gasoline vehicles, hot soak volatilization and motorcycles. Dong et al. (2014) carried out emission tests for motor vehicles based on different driving cycles such as the Vehicle Emission Control Center (VECC) and the World Transient Vehicle Cycle (WTVC), and analyzed carbonyl compounds based on the DNPH derivatization method with a source profile containing OVOCs (OVOCs, mainly aldehyde and ketone species) established. Tsai et al. (2012), Yao et al. (2013) and Yao et al. (2015) carried out emission tests for diesel vehicles, motorcycles and agricultural vehicles, analyzed their NMHCs and OVOCs emission characteristics, and established a more comprehensive source profile. Considering that motor vehicles are globally manufactured products with similar emission characteristics, foreign research results (Hsu et al., 2016; Schauer et al., 1999, 2002; Sigsby et al., 1987) have been employed. Since there was no aircraft emission related test research performed in China, the source profile of aircraft VOCs emission incorporated in SPECIATE was taken as the reference. As the main source of VOCs, solvent use mainly applied to industrial sectors of automobile paint use, furniture paint use and printing was substantially researched in China. Due to the severe fugitive emission from solvent use, many tests were conducted for profiles of fugitive emissions. The source profile work collected in this research mainly includes: Zheng et al. (2013) established the profiles of industrial sectors such as metal surface treatment, furniture paint use and shoemaking in the Pearl River Delta Region, and the emission of printing was tested and analyzed based on the classification of planographic printing, letterpress printing and gravure printing; Mo et al. (2015) established the profiles of automobile paint use, shipbuilding solvent use, container solvent use, woodware solvent use and other solvent uses with typical regional characteristics in Shanghai; Wang et al. (2014) established profiles of domestic and imported building paint use while compiling the industrial VOCs source profiles. Huang et al. (2011) tested the emissions of domestic solvent uses and established a source profile of solvent uses including floor and kitchen cleaner use. In addition, other relevant research projects at home and abroad were also included in the source profile database (Hsu et al., 2016; Yuan et al., 2010; Qiao, 2012). Except for fossil fuel burning, industrial sources and transportation, domestic profile research projects on other emission sources were relatively limited, which mainly focused on biomass burning. Wang et al.

(2009b) determined the VOCs source profile when fuel wood and crop stalks were used as fuels of stoves and heatable brick beds in rural areas in northern China. Tsai et al. (2003) established VOCs profiles of biomass particles forming fuel and crop stalk burning by analyzing the main domestic living fuels in China in the 1990s based on the combination of field tests and kitchen operation simulation. Zhang and Ma (2011) collected the NMHC species in the cooking fumes based on the main catering categories in Beijing, and established profiles of some catering categories. In addition, other profiles of biomass burning, storage and transportation, and solid waste treatment were collected as well (Hsu et al., 2016; Wang et al., 2013b; Andreae and Merlet, 2001; Zhang et al., 2013b; Lu et al., 2006). 2.3.2. Revision of source profiles without OVOCs In this research, VOCs were classified into Alkanes, Alkenes, Alkynes, Aromatics, Halohydrocarbons, OVOCs, and other VOCs. Some VOCs profiles do not contain OVOCs; however, as for OVOCs-rich sources such as motor vehicles and biomass burning, the aldehydes and ketones in OVOCs account for large proportions; therefore, it is necessary to revise the profiles without OVOCs. In fact, this work has been carried out for several sources such as petrochemical industry, chemical manufacturing and organic solvent use. In this paper, gasoline vehicles and diesel vehicles were taken as examples of transportation to illustrate the revision method. Please notice Fig. 3 for the revision process. Based on the revised method, it is required to select the profiles containing the OVOCs species from the alternative VOCs profiles, calculate the average mass fraction of the OVOCs species, take the mass fraction as the average OVOCs mass fraction of profiles of the same category, and introduce the mass fraction to the profiles of other sources of the same category that do not contain OVOCs. Please notice Equation (1).

Prei, j =

Pori i, j n Pori i, j j=1

× 1

Povocsi, j ?

(1)

where, i is the emission source; j is the VOCs species; n is the quantity of VOCs species; Prei,j is the mass fraction of j after the profile of i that does not include OVOCs species is revised and calculated; Porii,j is the mass fraction of j in the original profile of i that does not contain OVOCs species; Povocsi,j is the mass fraction of j in the source profile containing the OVOCs species; Povocsi, j is the average mass fraction of j in profiles including OVOCs species. It can be seen from Fig. 3 that, in the alternative profiles of gasoline vehicles, the average mass fraction of OVOCs species in the profiles of Schauer et al. (2002), Gao et al. (2012), Wang et al. (2013a) and SPECIATE (P_1203), which contain OVOCs species was 3.08%. This value was taken as the average mass fraction of OVOCs in the VOCs source profile of gasoline vehicles, and Equation (1) was employed for the calculation of other three profiles not containing OVOCs, so that the original mass fraction of species in the three profiles might be reduced to 96.92% to obtain the new OVOCs species mass fraction of 3.08%. The calculation method for diesel vehicles is also the same as that for gasoline vehicles. The mass fraction of OVOCs species in the 6 profiles of Schauer et al. (1999), Yao et al. (2015) and Tsai et al. (2012), which contain OVOCs species, was 36.58%. After the revision, the original mass fraction of species in other profiles that do not contain OVOCs species was reduced to 63.42%, and the new OVOCs species mass fraction was 36.58%. 2.3.3. Reconstruction of VOCs source profiles After the revision, the VOCs profiles were reconstructed. Taking the above-mentioned gasoline vehicle source profile as an example, after obtaining the source profile containing OVOCs, medians were taken for species of the 7 profiles to minimize the errors caused by abnormal samples and measured values. Then, the medians of species were added 4

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Fig. 3. Revision process of profiles for gasoline vehicles and diesel vehicles.

together to make the sum equal to 100% according to Equation (2), so as to obtain the reconstructed VOCs profiles. It is important to note that median calculation was performed for profiles containing OVOCs species only, and the revised OVOCs species in the original 3 profiles that do not contain OVOCs species were considered as missing values and were not incorporated in the calculation.

Ri, j =

Rmed i, j n Rmed i, j j=1

× 100%

mass fraction of j to that of the total VOCs in the pollution of i. As for the OFP calculation, the most widely used maximum incremental reactivity (MIR) was adopted to estimate the contribution of VOCs to ozone formation. The total amount of OFP in the pollution source was finally obtained by summing up OFPs from various species in the pollution source together. The calculation method is as Equation (4).

OFPi =

(2)

where, i is the emission source; j is the VOCs species; n is the quantity of VOCs species; Ri,j is the mass fraction of j in the revised profile, in which the emission source i is reconstructed; Rmedi,j is the median of j in the same revised source profile. Please notice R1 (gasoline vehicles) and R2 (diesel vehicles) in Fig. 4 for the reconstructed VOCs source profile. After the reconstruction of the gasoline vehicle VOCs source profile, it can be seen that methane was the species with the largest mass fraction up to 10.97%, followed by ethane (10.07%) and toluene (7.30%). The major species of the diesel vehicle source profile were formaldehyde (13.89%), styrene (10.77%) and acetaldehyde (10.49%). According to this method, all the collected VOCs profiles were reconstructed based on different emission source sub-categories to obtain the reconstructed profiles for the next calculation.

(4)

where, OFPi is the ozone formation potential of pollution source i; i is the type of pollution source; j is the species; Ei,j is the emission of j in pollution source i; MIRj is the maximum incremental reactivity of j with the factor obtained from Carter (2010). 2.4. Spatial distribution Different spatial distribution methods were selected based on different pollution sources and their emission characteristics, and the selected spatial distribution methods were implemented with GIS software and spatial proxies (mainly latitude and longitude, GDP, population, light distribution, land use distribution, road network, traffic flow, etc.). The parameters were mainly obtained from open source data such as Resource and Environmental Science Data Center (2015). Please notice the existing research (Zhou et al., 2018) for details.

2.3.4. Estimation of speciated emissions The emission of each species can be obtained based on the VOCs profiles. In order to further represent the contributions of the VOC species to secondary pollution, this paper conducted quantitative assessment over the activity of VOCs with OFP. The profiles were the normalized profiles after reconstruction. As for VOCs species emissions, corresponding profiles were distributed based on the total VOCs emission of pollution sources, so as to calculate the emission of a single species. Please notice Equation (3) for the calculation method.

Ei, j = E i ×fi, j

Ei, j × MIRj j=1

3. Result and discussions 3.1. Establishment of VOCs source profile database The VOCs source profile database, which includes a total of 45 sources classified into fossil fuel burning, industrial process, transportation, solvent use and other sources as shown in Fig. 5, was established based on the revision and reconstruction of the test data of the research literatures. As for pollution sources, such as civil fuels, motor vehicles and biomass burning, extensive tests and research projects were conducted based on different fuels, vehicle models and biomass types with

(3)

where, i is the emission source; j is the VOCs species; Ei,j is the emissions of j in the pollution of i; Ei is the VOCs emission of the source i; fi,j is the 5

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Fig. 4. Species with the highest 40 mass fractions in the reconstructed VOCs profiles (R1 represents the gasoline vehicles and R2 represents diesel vehicles).

several profiles established; however, the classification has been simplified and the number of profiles has been reduced for practical applications. Table 1 shows the comparison of VOCs source profile databases established at home and abroad. SPECIATE database v.4.5 is the most comprehensive VOCs source profile database, containing 2175 profiles, most of the pollution sources, and more than 2000 species. The European VOCs source profile includes 87 profiles and 306 species. In China, Wei et al. (2014) established a source profile database including 42 profiles and 33 species based on domestic field research projects and SPECIATE database; Mo et al. (2016) established a source profile database containing 75 species based on a large number of domestic field research projects; through statistical methods, Li et al. (2014)

established a comprehensive source profile database containing 700 species based on the SPECIATE database supplemented by collected domestic measured data. Since the profiles in this paper were established mainly based on domestic test data, SPECIATE was employed to supplement the profiles of some sources that had not been actually measured or had been researched less in China. In addition, the profiles of some sources such as biomass burning and transportation with emissions containing rich OVOCS have been revised and reconstructed. Therefore, the established source profile database is well applicable to the establishment of the speciated VOCs emission inventory and source apportionment. It can be seen from Fig. 5 that, in the VOCs source profile established in this paper, OVOCs is the leading species type of diesel vehicles

Fig. 5. Estanblishment of VOCs profiles. 6

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Table 1 Comparison of VOCs source profile databases of US, Europe and China. Source

Source of the profile

Quantity of profiles

Contained species

Application area

USEPA SPEICATE,2016 Theloke and Friedich (2017) Wei et al. (2014) Li et al. (2014) Mo et al. (2016) This paper

Mainly the tests and research projects of USA and Canada Mainly the tests and research projects of the UK and Germany Domestic tests and research projects and SPECIATE database Domestic tests and research projects and SPECIATE database Domestic tests and research projects Domestic tests and research projects and SPECIATE database, etc

2175 87 42 55 85 45

~2000 306 33 ~700 75 519

USA Europe China China China Sichuan

corresponding OFPs in Sichuan Province was established based on the VOCs source profile database in Section 3.1 (the source types not directly given were replaced by similar source types). The emissions of various VOCs species and their OFPs are shown in Fig. 6. The total emissions of anthropogenic VOCs in Sichuan Province were 773.8 kt, of which alkane, alkene, alkyne, aromatic hydrocarbon, OVOCs, halogenated hydrocarbons and other components accounted for 21.6%, 10.0%, 1.7%, 28.0%, 26.2%, 4.2% and 8.3% respectively. The total OFP was 2584.9 kt, and the above-mentioned VOCs contributed 6.9%, 26.1%, 0.5%, 42.3%, 23.2%, 0.4%, and 0.5% to the total OFP respectively. Therefore, it was concluded that the OFP contributions of various types of VOCs in Sichuan Province varied greatly. The alkenes and aromatics with relatively high atmospheric chemical reactivities contributed OFP by over twice as much as their VOCs emission proportions, OVOCs contributed OFP by about its VOCs emission proportion, while alkanes with relatively low atmospheric chemical reactivity and in large emission contributed OFP by only 6.9%. Therefore, alkenes and aromatics were the key species of VOCs in Sichuan for ozone formation, and controlling their emissions may play a key role in reducing ozone formation. Fig. 6 also shows the contribution rates of various VOCs emission sources. The primary source of alkanes and alkenes was transportation, which contributed 45% and 37% of their respective total emissions from various sources; the primary source of aromatics, OVOCs and halohydrocarbons was solvent use, which contributed 46%, 42%, and 60% of their respective total emissions; the major source of alkynes and halohydrocarbons was industrial process, which contributed 44% and 37% to their respective total emissions; the main source of OVOCs included biomass burning as well, which contributed 24% of the total emission. In general, control measures shall be taken against the major sources of alkenes, aromatics and OVOCs: industrial process,

and biomass burning. Please notice Table 2 and Table 3 for comparisons of VOCs species and chemical group contributions between diesel vehicle emissions and biomass burning in different research projects. It can be seen from Table 2 that, as for the mass fraction of OVOCs in VOCs, the research result of Tsai et al. (2012) was significantly lower than those of other research projects; in addition, the mass fraction of aromatics in VOCs was also significantly different from the results of other research projects. However, the mass fractions of OVOCs and aromatics in this paper were within the range of these research results; all the species with the highest ten mass fractions in the diesel vehicle source profile established in this paper were characteristic species, such as formaldehyde, styrene and acetaldehyde, which were consistent with those in other research projects. It can be seen from Table 3 that the mass fractions of OVOCs in VOCs were relatively large in different biomass burning research projects, and the mass fraction in this paper has reached up to over 50%, which was within the range between the mass fractions in other two research projects. Since the research of Andreae and Merlet (2001) contains a variety of biomass fuels, the mass fractions of different OVOCs in VOCs fluctuated greatly, and the research result of Mo et al. (2016) was similar to the former one. In general, since the source profile in this paper was reconstructed based on other research projects, the established VOCs source profile database was a synthesis of different research projects, which may effectively reduce the uncertainty caused during the selection of profiles due to the differences of test processes, objects, methods and species in different research projects in practical applications. 3.2. Speciated VOCs emission contributions of anthropogenic sources in Sichuan Province The 2015 VOCs emission inventory containing 519 species and

Table 2 Comparison of species and chemical group contributions for diesel vehicle exhaust/%. This paper

Yao et al. (2015)

a

Tsai et al. (2012)

b

Schauer et al. (1999)

Species

Mass fraction

Species

Mass fraction

Species

Mass fraction

Species

Mass fraction

Formaldehyde Styrene Acetaldehyde N-undecane Ethane Ethene 1,2,4-trimethyl benzene Propyl aldehyde Acetylene Methyl ethyl ketone Sum of the top ten species Alkanes Alkenes Alkynes Aromatics Halohydrocarbons OVOCs Other VOCs

9.0 7.0 6.8 5.8 3.2 2.9 2.5 2.4 1.9 1.8 43.4 19.1 8.3 1.9 22.9 – 37.7 10.1

Formaldehyde Acetaldehyde Ethene Acetylene Propyl aldehyde Isopentane Toluene Acrolein Crotonaldehyde m-Xylene Sum of the top ten species Alkanes Alkenes Alkynes Aromatics Halohydrocarbons OVOCs Other VOCs

19.3–40.2 8.4–14.3 4.3–4.6 3.1–5.0 3.7–3.9 1.8–5.8 2.6–4.5 1.8–3.2 1.9–2.9 1.7–2.6 57.6–78.0 4.5–14.6 6.3–.6.7 3.1–5.0 7.8–11.8 – 42.4–68.3 10.1–19.5

N-propyl benzene Styrene N-undecane o-Xylene O-ethyl toluene 1,2,4-trimethyl benzene Toluene Formaldehyde Ethyl benzene Isopropyl benzene Sum of the top ten species Alkanes Alkenes Alkynes Aromatics Halohydrocarbons OVOCs Other VOCs

13.4 10.8–14.1 9.0–11.7 5.2–7.0 3.9–6.6 4.5–5.5 2.6–5.3 2.9–4.7 2.8–3.5 1.2–4.4 60.7–71.6 12.7–17.7 2.0–4.1 – 55.4–66.8 – 9.0–12.6 3.7–16.0

Acetaldehyde Formaldehyde Propyl aldehyde Crotonaldehyde Ethene Methyl ethyl ketone Methyl phenyl ketone Acetylene Nonanal Methacrolein Sum of the top ten species Alkanes Alkenes Alkynes Aromatics Halohydrocarbons OVOCs Other VOCs

15.9 8.5 5.3 5.1 3.3 2.9 1.9 1.8 1.7 1.5 48.0 9.6 4.9 1.8 5.9 – 57.2 20.7

a b

The test results of light-duty, medium-duty and heavy-duty diesel vehicles were considered comprehensively. The test results of two driving cycles were considered comprehensively. 7

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Table 3 Comparison of species and chemical group contributions for biomass burning/%. This paper

Andreae and Merlet (2001)

Mo et al. (2016)

Species

Mass fraction

Species

Mass fraction

Species

Mass fraction

Alkanes Alkenes Alkynes Aromatics Halohydrocarbons OVOCs Other VOCs

9.7 11.4 1.9 11.1 0.5 58.8 6.5

Alkanes Alkenes Alkynes Aromatics Halohydrocarbons OVOCs Other VOCs

4.8–6.0 4.1–28.9 0.2–3.8 1.6–25.0 0.1–1.7 28.9–87.9 1.0–1.5

Alkanes Alkenes Alkynes Aromatics Halohydrocarbons OVOCs Other VOCs

0.2–1.0 10.6–23.2 – 25.0–45.5 0.8–1.7 22.3–43.6 4.1–5.9

Fig. 6. VOCs emission contributions of anthropogenic sources in Sichuan Province kt/a.

Fig. 7. VOCs species with the highest 20 OFPs from different emission sources and sub-sources kt/a. 8

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transportation, solvent use and biomass burning. In addition, since industrial process and solvent use may cause great emission of halohydrocarbons, management over the pollution sources shall be strengthened. Industrial process, transportation and solvent use were relatively complex and their OFPs were relatively large; Fig. 7 shows the emissions of 20 VOCs species with the highest OFPs of 3 pollution sources and the anthropogenic sources in Sichuan Province as well as the emission contributions of these pollution sources for analysis. However, the results were calculated with relatively high uncertainty due to the lack of or inaccuracy of some VOCs profiles and the omission of some emission sources. Fig. 7 shows that it was the difference of the VOCs chemical reactivities, ie MIRs, that caused the great change in the arrangement order of the 20 species with the highest OFPs and their corresponding emissions, especially the aromatics, alkenes, OVOCs and other species with relatively high MIRs. Some OVOCs, such as glyoxal and methyl glyoxal had relatively high OFPs when their emissions were relatively low due to their extremely high chemical reactivity, while alkanes (nhexane and isopentane), acetylene and some OVOCs (ethyl acetate and methyl ethyl ketone) had relatively low OFPs relative to their emissions due to their low chemical reactivity. Furthermore, it can be seen from Fig. 7(a) that: except that the main emission source of some OVOCs species was biomass burning (96% for glyoxal, 96% for methyl glyoxal, and 94% for biacetyl), solvent use, industrial process and transportation were the major sources of VOCs in Sichuan Province; as the species ranking fourth in the VOCs emissions, m-Xylene caused the most OFP, and it was mainly caused by solvent use (65%), transportation (17%) and industrial process (16%); with similar emission sources, other aromatics such as toluene, o-Xylene and ethylbenzene also made relatively high OFP contributions; the main alkenes ozone precursors include ethene, propylene, 1-butene, trans-2butene and cis-2-butene, and ethene was the second largest source of OFP. It can be seen from Fig. 7(b) that industrial process sources of various species varied greatly: alkenes were mainly caused by the manufacturing of nonmetal mineral products (mainly the manufacturing of cement, glass and bricks), and petrochemical industry was also the main emission source of 1-pentene; the main source of aromatics was the manufacturing of nonmetal mineral products and chemical materials and chemicals; the OVOCs species were mainly derived

from the manufacturing of artificial board and materials and chemicals; acetylene was mainly caused by the manufacturing of nonmetal mineral products as well. Fig. 7(c) shows that the main sources of transportation mainly included gasoline automobiles, diesel automobiles, motorcycles and construction machinery. The OVOCs mainly came from the emissions of diesel automobiles and construction machinery. Fig. 7(d) shows that the VOCs species from solvent use with relatively large OFPs were aromatics, and the main emission sources were furniture paint use, automobile paint use, metal surface treatment, interior wall latex paint use and other industries, which mainly involve paint use. Except that dlimonene was mainly caused by domestic solvent use, the remaining alkene species were mainly emitted from automobile paint use, printing and interior wall latex paint use; in addition, electronics equipment manufacturing, metal surface treatment, shoemaking and domestic solvent use were the main sources of OVOCs. 3.3. Emission characteristics of urban anthropogenic VOCs in Sichuan Province Fig. 8 shows the emission characteristics of urban anthropogenic VOCs in Sichuan Province. The major emission species of VOCs in various cities were aromatics, OVOCs and alkanes, which were generally consistent with the status of Sichuan Province. However, different cities have their own remarkable characteristics: in Chengdu, onroad motor vehicle emissions made great contributions to VOCs, and alkanes accounted for a relatively high proportion in the total VOCs emission; since Panzhihua is a traditional heavy industry city, VOCs were mainly caused by the industrial process (mainly the coking), alkanes accounted for a relatively high proportion in the total VOCs emission; the major pollution source in Deyang (electronics equipment manufacturing), Meishan (textile and equipment coating), Suining (electronics equipment manufacturing and furniture paint use) and Ziyang (shoemaking) was solvent use, which resulted in a relatively high proportion of OVOCs emissions in the total VOCs emission; onroad motor vehicle emissions were the major pollution sources in Ya'an, Aba, Ganzi and Liangshan; since the industries in Aba and Ganzi were less developed and on-road motor vehicle emissions accounted for up to more than 65% in their total VOCs emissions, their alkane emissions accounted for relatively high proportions as well.

Fig. 8. Emission characteristics of anthropogenic VOCs in cities in Sichuan Province kt/a.

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Fig. 9. Spatial distribution of typical VOCs emissions in Sichuan Province (a. m-Xylene, b. ethene, c. toluene and d. formaldehyde).

3.4. Spatial distribution of anthropogenic speciated VOCs emissions in Sichuan Province

widely distributed in the whole area of Chengdu as well as the central areas of other cities. Since transportation was a major source of the 4 species, emissions of the 4 species had significant road emission characteristics; however, there were still some differences in their distributions due to the characteristics of other major sources: the main source of m-Xylene and toluene was solvent use; therefore, they were more intensively distributed in urban built-up areas. Furthermore, since biomass burning contributed a lot to ethene and formaldehyde emissions, ethene and formaldehyde were greatly distributed in cultivated areas in eastern Sichuan and southern Sichuan.

Fig. 9 shows the 1 km × 1 km resolution-based spatial distribution of four VOCs species with relatively large OFPs (m-Xylene, ethene, toluene and formaldehyde). The emissions of more than 500 VOCs species were distributed in the grids of the same resolution as the method specified in Section 2.4. The spatial distribution data of VOCs species emissions were helpful to compare emissions data of emission sources with online monitoring data or for VOCs source apportionment. Upon the selection of different profiles, the emissions of some species may vary by orders of magnitude. Therefore, when the online monitoring data are explained with species emissions, the VOCs species emissions should be used prudently. It can be seen from Fig. 9 that since the four species were mainly emitted from industries, motor vehicles and interior wall latex paint use, their emissions were mainly distributed in Sichuan basin (including Chengdu, Mianyang, Luzhou, Nanchong, Zigong, Deyang, Guangyuan, Suining, Neijiang, Leshan, Yibin, Guang'an, Dazhou, Ya' an, Bazhong, Meishan and Ziyang), as well as some areas of Liangshan and Panzhihua, which are the most densely populated areas with relatively developed industry, i.e. emissions of these species were

4. Conclusions A complete VOCs source profile database and a highly resolved temporal and spatial speciated anthropogenic VOCs emission inventory in Sichuan Province were developed by using the local source information, energy consumption, other information and the best available knowledge in this research. The inventory was compiled for the use in air quality models. Based on the test data of the research literatures, the source profile of species not containing OVOCs was revised and reconstructed to obtain normalized VOCs profiles and establish a VOCs 10

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source profile database including 45 profiles and 519 species. Since the profiles were established mainly based on domestic test data, foreign research results were employed to supplement the profiles of some sources that had not been actually measured or had been researched less in China. In addition, the profiles of some sources such as biomass burning and transportation with emissions containing rich OVOCs have been revised and reconstructed, and the profiles including redundant data of many tested sources were simplified accordingly as well. Therefore, the established source profile database is well applicable to the establishment of the speciated VOCs emission inventory and source apportionment. The 2015 VOCs emission inventory of anthropogenic sources in Sichuan Province including 519 VOCs species and their OFPs showed that the total VOCs emissions from anthropogenic sources in Sichuan Province were 773.8 kt, mainly consisting of aromatics, OVOCs and alkanes; the total OFP emissions were 2584.9 kt with the OFPs of the above three VOCs accounting for 42.3%, 23.2% and 26.1%, respectively; therefore, controlling the three VOCs plays a key role in the reduction of ozone formation. Furthermore, measures shall be taken to control the industrial process, transportation, solvent use and biomass burning, which are the main contributors to olefins, aromatics and OVOCs. In addition, since industrial process and solvent use may cause great emission of halohydrocarbons, management over the pollution sources shall be strengthened. The major VOCs species in cities of Sichuan Province included aromatics, OVOCs and alkanes; however, there were still some differences in the emission and distribution of VOCs between these cities due to various industrial structures and levels of economic development. The speciated VOCs emission inventory established in this paper may better represent the anthropogenic VOCs emission characteristics of Sichuan Province; nevertheless, it is still necessary to perform further localization research on the VOCs source profiles of some pollution sources to reduce the data errors in the emission inventory caused by differences between the production processes and emission control levels in Sichuan Province and these factors in other regions at home and abroad.

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