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Article Sources Profiles of Volatile Organic Compounds (VOCs) Measured in a Typical Industrial Process in Wuhan, Central China

Longjiao Shen 1,2, Ping Xiang 3, Shengwen Liang 2, Wentai Chen 3, Ming Wang 4, Sihua Lu 5 and Zuwu Wang 1,*

1 School of Resource and Environmental Science, Wuhan University, Wuhan 430079, China; [email protected] 2 Environmental Monitoring Center of Wuhan, Wuhan 430022, China; [email protected] 3 Nanjing Intelligent Environmental Sci-Tech Company Limited, Nanjing 211800, China; [email protected] (P.X.); [email protected] (W.C.) 4 College of Environmental Science and , Nanjing University of Information Science and Technology, Nanjing 210044, China; [email protected] 5 State Joint Key Laboratory of Environmental Simulation and Control, College of Environmental Sciences and Engineering, Peking University, Beijing100871, China; [email protected] * Correspondence: [email protected]

 Received: 30 June 2018; Accepted: 24 July 2018; Published: 30 July 2018 

Abstract: Industrial emission is an important source of ambient volatile organic compounds (VOCs) in Wuhan City, Hubei Province, China. We collected 53 VOC samples from petrochemical, surface , electronic , and gasoline evaporation using stainless canisters to develop localized source profiles. Concentrations of 86 VOC species, including hydrocarbons, halocarbons, and oxygenated VOCs, were quantified by a gas –flame ionization detection/mass spectrometry system. were the major constituents observed in the source profile from the petrochemical . Aromatics (79.5~81.4%) were the largest group in auto-painting factories, while oxygenated VOCs (82.0%) and heavy alkanes (68.7%) were dominant in gravure and offset printing factories, respectively. was the largest contributor and the most frequently monitored species in printed circuit board (PCB) manufacturing, while VOC species emitted from integrated chip (IC) were characterized by high contents of isopropanol (56.4–98.3%) and acetone (30.8%). Chemical compositions from vapor of gasoline 92#, 93#, and 98# were almost identical. Alkanes were the dominant VOC group, with i-pentane being the most abundant species (31.4–37.7%), followed by n- and n-pentane. However, high loadings of heavier alkanes were observed in the profile of diesel evaporation.

Keywords: VOCs; source profile; industrial; gas station; Wuhan

1. Introduction Study on volatile organic compounds (VOCs) has attracted increasing attention because of their important roles in the formation of ozone and secondary organic aerosols, which can impact climate change and air quality and are hazardous to human health and production [1–4]. Recent studies indicated that urban areas in China are suffering from serious haze and photochemical smog, which is associated with the reactive VOC components [5,6]. This implies that the control of VOCs emissions should be one of the priorities for China’s air quality improvement. Due to the diversity, complexity, and disorganized characteristics of VOC emission sources, control of VOCs has been challenging [7–9]. Accurate and reliable VOCs source profiles are fundamental tools for research on the establishment of

Atmosphere 2018, 9, 297; doi:10.3390/atmos9080297 www.mdpi.com/journal/atmosphere Atmosphere 2018, 9, 297 2 of 18 speciated VOC emission inventory and for other studies such as source apportionment, assessments of human exposure to toxic and hazardous substances, and simulation of regional air quality [10,11]. On the other hand, local source profile is also essential for policy makers to conduct reactivity-based VOC emission abatement and formulate efficient O3 control strategies. VOC source profiles explain the composition pattern of species emitted from a specified source category and are usually expressed as the weight fraction of individual VOC species relative to the total mass concentration of all VOC species measured [12]. The SPECIATE database established and integrated by the US Environmental Protection Agency (EPA) is currently the most comprehensive repository for source category-specific emission speciation profiles, with almost 2000 VOC species and 1700 profiles included [13]. Europe, Korea, and other countries and regions have also developed their own domestic source profiles. However, studies on emission characteristic of VOCs from anthropogenic sources in China are incomplete and unorganized and mainly focus on densely populated and economically developed regions such as the Yangtze River Delta region (YRD), the Pearl River Delta region (PRD), and Beijing [11,14]. VOC sources in China are quite complex because of the diversity of energy use and industry structures in different cities. Therefore, local VOC source profiles are necessary for the further work on local VOCs control. Industrial activities are considered as the major anthropogenic VOCs emission sources in China [15–17]. In this study, Wuhan was chosen as the typical city in central China, and measurements of local VOC emission sources were performed with a focus on industrial process. Wuhan is the largest megacity in central China and is also an important transport hub [18], with large industrial activity concentrated at the southwest and northeast of the downtown. According to the emission inventory established in 2015 by the local environmental monitoring center, industries constituted the top emitter of VOCs in Wuhan, reaching 38.7% of the total VOC emissions. Three major industrial source categories including refinery, surface coating and painting, and the electronics manufacturing industry were selected because they have been known to emit significant quantities of VOCs. The source profile of fuel evaporation from gas stations was measured since gasoline and diesel vapor were also an important contributor to ambient VOCs. The main objectives of this manuscript are (1) to develop local VOCs source profile with a focus on industrial process, (2) to identify the characteristic species of different industrial sector, and (3) to compare this study with other similar researches so that recognizing the similarities and differences of typical industrial VOC source profiles in China. The results and implications from this study are fundamental for the establishment of a speciated VOC emission inventory that can help the Wuhan local government conduct reactivity-based VOC abatement and further alleviate O3 pollution.

2. Materials and Methods

2.1. Source Sampling A total of 53 samples covered four major VOCs source categories in Wuhan were collected during 2016–2017 to build the localized source profiles. The standard operating procedures (SOPs) issued by Ministry of Environmental Protection (2013) were followed to ensure consistent procedures throughout the field sampling. Samples were collected in 3.2 L electro-polished stainless-steel canisters and 86 VOCs species were quantified with a gas chromatography–mass spectrometry/flame ionization detection (GC–MS/FID, Agilent GC7820A, MS5977B). In this study, source samples were instantaneously collected into canisters. The sampling time was about 2 min. A brief description of the source sampling is shown below.

2.1.1. Petrochemical Industry To characterize the chemical speciation of VOCs from the petroleum refinery, a total of nine samples were collected inside the manufacturing facilities as depicted in Figure1. All of the units could be divided into three categories: refinery (OR), storage tank (ST), and wastewater treatment Atmosphere 2018, 9, 297 3 of 18

Atmosphere 2018, 9, x FOR PEER REVIEW 3 of 18 (WT). Six samples including regular and reduced pressure (CDU & VDU, OR1), reforming hydrogenation (OR2), catalytic (OR3), catalytic hydrogenation (OR4 with wax oil and OR5 with gasoline and diesel), and delayed coking (OR6) were taken in the refinery sector. Leakage of storage tanks and wastewater wastewater treatment facilities were also previously identified identified as the major fugitive fugitive emission sources [19–21]. [19–21]. Therefore, samples from two tanks where lower olefins olefins (ST1) and gasoline stored (ST2) and one wastewater treatment sectorsector for oil separating (WT) werewere collected.collected.

Figure 1. Location of the nine sampling sites in the petroleum plants. Figure 1. Location of the nine sampling sites in the petroleum plants.

2.1.2. Surface Coating and Printing 2.1.2. Surface Coating and Printing Industrial use is an important source for anthropogenic VOCs emissions, which includes Industrial solvent use is an important source for anthropogenic VOCs emissions, which includes application, printing processes, dry cleaning, solvent evaporation from household products, paint application, printing processes, dry cleaning, solvent evaporation from household products, and other [14]. In this study, compositions of VOCs emitted from surface coating and other industrial processes [14]. In this study, compositions of VOCs emitted from surface coating (auto manufacturing and equipment coating) and printing were sampled and measured according to (auto manufacturing and equipment coating) and printing were sampled and measured according to the local industrial structure and VOCs emissions. the local industrial structure and VOCs emissions. Specifically, a total of 16 valid emission samples covering the major crafting processes were Specifically, a total of 16 valid emission samples covering the major crafting processes were collected from four sectors of a local automobile manufacturing enterprise: three samples (EC1–EC3) collected from four sectors of a local automobile manufacturing enterprise: three samples (EC1–EC3) were taken in different processes in primer coating section, which is the first step of auto painting, were taken in different processes in primer coating section, which is the first step of auto painting, and the electro-coating method was used to create an organic binding layer to modify the car surface and the electro-coating method was used to create an organic binding layer to modify the car surface in preparation for subsequent coating processes. Three samples were collected in the sealing section in preparation for subsequent coating processes. Three samples were collected in the sealing section (S1–S3), in which composition ratios of VOCs were not adequately measured by previous studies. (S1–S3), in which composition ratios of VOCs were not adequately measured by previous studies. Moreover, since top-coating was regarded as the major source in auto industry due to the Moreover, since top-coating was regarded as the major source in auto industry due to the volatilization volatilization of organic during spraying, flash-off, and drying processes, a large emphasis of organic solvents during spraying, flash-off, and drying processes, a large emphasis was given to the was given to the measurement of VOCs from this sector where six source samples (TC1–TC6) were measurement of VOCs from this sector where six source samples (TC1–TC6) were collected. Finally, collected. Finally, VOCs emitted from baking room after treating by regenerative thermal oxidation VOCs emitted from baking room after treating by regenerative thermal oxidation (RTO) technology (RTO) technology were also sampled (RTO1–RTO4). were also sampled (RTO1–RTO4). For the equipment coating industry, an air-conditioning facility was selected, and four samples For the equipment coating industry, an air-conditioning facility was selected, and four samples from coating process were measured. Meanwhile, samples of two kind of printing, namely gravure from coating process were measured. Meanwhile, samples of two kind of printing, namely gravure printing and offset printing, were also collected in two printing facilities. printing and offset printing, were also collected in two printing facilities. 2.1.3. Electronic Manufacturing Industry According to the work flows and electronic product processes, painting and cleaning workshops are two major sectors involved VOCs release due to the use of and . In this study, typical electronic industries in Wuhan City including PCB and integrated circuit chip (IC) manufacturing were experimentally investigated.

Atmosphere 2018, 9, 297 4 of 18

2.1.3. Electronic Manufacturing Industry According to the work flows and electronic product processes, painting and cleaning workshops are two major sectors involved VOCs release due to the use of coatings and detergent. In this study, typical electronic industries in Wuhan City including PCB and integrated circuit chip (IC) manufacturing were experimentally investigated.

2.1.4. Emission from Gas Station Fugitive emissions from oil production, usages, storage, and delivery are the major sources of emissions from fuels [22]. There are usually four kinds of methods to experimentally measure the structures of VOCs emissions from gasoline and diesel evaporation: (1) hot soak experiment, which is driven by residual engine heat; (2) 24 h day-and-night evaporation test from the vehicle at rest due to the diurnal variation of temperature; (3) headspace analysis, in which ample direct fuel vapor was taken from a sealed with the fuels half filled; and (4) refueling loss measurement, which occurs during the refueling process due to dripping and vapors displacement [12]. In this paper, source profile of fuels evaporation in Wuhan City was measured and estimated by samples collected during filling vehicles tanks at the gas station. Based on urban fleet and gasoline sales, three types of widely consumed gasoline (grade 92#, 95#, and 98# octane) and one type of diesel fuel (0# diesel) were chosen for source profile measurements. Canister sampling was performed 1 m downwind of the refueling gun to measure the evaporation from oil. A total of nine samples in accordance with China V were collected including three for Grade 92# gasoline and two samples for each of the other fuels (Grade 95#, 98#, and 0# diesel).

2.2. VOCs Analysis and QA/QC The VOC chemical speciation of these samples was analyzed by GC-MS/FID system, and 86 VOC species were quantified. The VOC analysis procedures followed US EPA methods TO-14 and TO-15. Sources samples was collected using 3.2 L fused silica stainless-steel canisters that had been pre-cleaned with high-purity nitrogen (purity N 99.999%) and evacuated with an automated canister cleaning system (Entech 7100; Entech Instruments Inc., Simi Valley, CA, USA). Each sample was concentrated using a three-stage cryofocusing pre-concentration system (Entech 7200; Entech Instruments Inc., Simi Valley, CA, USA). H2O and CO2 were removed in the first two cryotraps using glass beads and Tenax-TA adsorbents, respectively. VOCs were then trapped at −180 ◦C in the final stage, and the trap was rapidly heated, after which VOCs were transferred into the gas chromatography–mass spectrometry/flame ionization detection (GC–MS/FID) system for analysis (GC, HP-7820; MSD, HP-5977B; Hewlett-Packard, Palo Alto, CA, USA). This system used a Dean Switch™ (Agilent Technologies, Santa Clara, CA, USA) to introduce the effluent into a DB-624 column (60 m × 0.25 mm × 1.4 µm; J&W Scientific, Folsom, CA, USA) with an MSD to separate and analyze compounds (C6–C12 hydrocarbons, Halogenated hydrocarbons and OVOCs) and a PLOT (Al2O3) column (15 m × 0.32 mm × 5.0 µm; Dikma Technologies Inc., Massier Ln, CA, USA) with an FID to measure the C2–C6 hydrocarbons. The GC oven temperature was programmed initially at 37 ◦C for 5 min, increasing to 120 ◦C at 5 ◦C/min and holding for 5 min, and then increasing to 180 ◦C at 6 ◦C/min and holding for 5min. The entire process took ~41.6 min. The carrier gas was pure helium (purity N 99.999%). The MSD was operated in the scan mode with amass range of 29–350 amu. The ionization method was electron impact (EI, 70 eV). During the analysis process, strict protocols for quality control and quality assurance were used. The standard gas including Photochemical Assessment Monitoring Stations (PAMS) standard (57NMHCs) and TO-15 standard mixture (65 compounds, from Linde Spectra Environment Gases, Alpha, NJ, USA) was used to calibrate the C2–C12 VOCs. Calibration was performed at five different concentrations from 0.5 to 8 ppbv by the 57 PAMS gas standard and 65 TO-15 gas standard. Bromochloromethane, 1,4-difluorobenzene, -d5, and 4-Bromofluorobenzene were used Atmosphere 2018, 9, 297 5 of 18 as internal standards for each sample to calibrate the system. The precision of each species was within 10%. A gas standard (diluting from 1 ppm to 2 ppbv) was measured each day to check the stability of the system. The method detection limits (MDL) for various compounds ranged from 2 to 50 pptv. The species list composed of 28 alkanes, 11 , 1 alkyne, 16 aromatic compounds, and 24 halocarbons was presented in Table1.

Table 1. Volatile (VOC) species measured in emission samples.

No. Species No. Species No. Species Alkanes(28) 31 trans-2- 61 Ethyl acetate 1 32 1-Butene 62 i-Propanol 2 33 cis-2-Butene Halocarbons(24) 3 i-Butane 34 1,3- 63 Freon11(CFCl3) 4 n-Butane 35 1-Pentene 64 Freon12(CF2Cl2) 5 Cyclopentane 36 trans-2-Pentene 65 Freon114(C2F4Cl2) 6 i-pentane 37 66 Chloromethane 7 n-Pentane 38 cis-2-Pentene 67 Dichloromethane 8 2,2-Dimethylbutane 39 1- 68 Chloroform 9 2,3-Dimethylbutane 40 Acetylene 69 Carbontetrachloroide 10 2-Methylpentane Aromatics(16) 70 Chloroethane 11 3-Methylpentane 41 71 1,1-Dichloroethane 12 n-Hexane 42 72 1,2-Dichloroethane 13 2,4-Dimethylpentane 43 73 1,1,1-Trichloroethane 14 Methylcyclopentane 44 m/p- 74 1,1,2-Trichloroethane 15 2-Methylhexane 45 o-Xylene 75 1,2-Dichloropropane 16 46 76 1,1-Dichloroethylene 17 2,3-Dimethylpentane 47 i-Propylbenzene 77 18 3-Methylhexane 48 n-Propylbenzene 78 19 2,2,4-Trimethylpentane 49 3-Ethyltoluene 79 trans-1,3-Dichloropropene 20 n-Heptane 50 4-Ethyltoluene 80 Bromomethane 21 Methylcyclohexane 51 1,3,5-Trimethylbenzene 81 Bromoform 22 2,3,4-Trimethylpentane 52 1,2,4-Trimethylbenzene 82 Bromodichloromethane 23 2-Methylheptane 53 1,2,3-Trimethylbenzene 83 Chlorobenzene 24 3-Methylheptane 54 2-Ethyltoluene 84 1,3-Dichlorobenzene 25 Octane 55 1,3-Diethylbenzene 85 1,4-Dichlorobenzene 26 n- 56 1,4-Diethylbenzene 86 1,2-Dichlorobenzene 27 n-Decane OVOCs(6) 28 n-Undecane 57 Alkenes(11)/Alkyne(1) 58 Acetone 29 59 MTBE 30 Propylene 60 Methyl ethyl ketone

3. Results and Discussion Source profiles were obtained by averaging the weighted percentages of individual VOC species relative to the sum of all quantified VOCs. The numbers in the source profiles correspond with the number per compound as given in Table1. Detailed emission values appear in the Supplementary Materials.

3.1. Petrochemical Industry The total mass concentrations and chemical structures of the 86 analyzed VOC species measured at various process units are depicted in Figure2. Figure2 illustrated the overall VOC group patterns and the sum of all measured VOCs (TVOCs) mass concentration from different processes including oil refinery (OR1–OR6), storage tank (ST1,ST2), and wastewater treatment (WT). The highest mass concentration of TVOCs reaching 36,302 µg/m3 was observed in the WT sector, confirming that wastewater treatment facilities were important in the process of VOC emissions. The mass concentrations of VOCs varied from 132 to 1377 µg/m3 in oil refinery units, while significant variations Atmosphere 2018, 9, 297 6 of 18 Atmosphere 2018, 9, x FOR PEER REVIEW 6 of 18 wereof TVOCs found were between detected, the olefin respectively. tank and gasoline This obvi tank,ous where difference 405 µ g/mmay3 attributedand 4630 µ g/mto the3 of different TVOCs wereemission detected, strength respectively. and diffusion This conditions obvious difference during sampling. may attributed to the different emission strength and diffusionChemical conditions structures during of the sampling.various processes showed that alkanes were the dominant VOC groupChemical in all sectors, structures accounting of the variousfor 41.1–97.4% processes of showedthe total thatVOCs alkanes mass wereconcentration the dominant (Figure VOC 2). groupTo be inspecific, all sectors, in the accounting refining process for 41.1–97.4% of CDU&VDU of the total (OR1 VOCs), reforming mass concentration hydrogenation (Figure (OR2),2). To and be catalytic specific, incracking the refining (OR3), process alkanes of were CDU&VDU the most (OR1), abundant reforming VOC hydrogenationgroup with a range (OR2), of and67.0–82.5%, catalytic followed cracking (OR3),by aromatics alkanes (4.6–22.8%) were the most and abundant alkenes (3.8–11.0%). VOC group Emission with a range from of two 67.0–82.5%, catalytic followed hydrogenation by aromatics units (4.6–22.8%)with different and raw alkenes materials (3.8–11.0%). (OR4 with Emission wax oil from and two OR5 catalytic with gasoline hydrogenation and diesel) units exhibited with different some rawdiscrepancies. materials (OR4Aromatics with and wax alkenes oil and represent OR5 with much gasoline higher and percentages diesel) exhibited of the some total discrepancies.VOCs in OR4 Aromaticsrather than and that alkenes in OR5. represent Coking muchunits higher(OR6) ha percentagesd a different of thechemical total VOCs structure in OR4 where rather the than highest that inlevels OR5. of CokingOVOCs units contributed (OR6) had to the a different total mass. chemical Due to structure the fact that where the the raw highest materials levels and of products OVOCs contributedstored in the to two the tanks total mass.were different, Due to the a facthigher that pe thercentage raw materials of alkenes and were products detected stored at the in the olefins two tankstank (accounting were different, for 22.9% a higher of percentagethe total) rather of alkenes than that were of detected the other at units, the olefins while tankalkanes (accounting contributed for 22.9%over 97% of the to total)the total rather VOCs than from that the of thegasoline other units,tank. For while the alkanes wastewater contributed treatment over of 97% oil separating, to the total VOCsalkanes from were the also gasoline the most tank. prevalent For the wastewaterspecies (90.5%), treatment followed of oil by separating, aromatics, alkaneswhich accounted were also thefor most7.3% of prevalent the total species VOC emissions, (90.5%), followed similar to by that aromatics, (6.1–7.7%) which of wastewater accounted treatment for 7.3% of reported the total by VOC Mo emissions,et al. (2015). similar to that (6.1–7.7%) of wastewater treatment reported by Mo et al. (2015).

Figure 2. Overall chemical group patterns of VOCVOC emissionsemissions from eacheach petroleumpetroleum unit.unit. (Note: OR1: CDU&VDU; OR2: reforming hydrogenation; OR3: catalyticcatalytic cracking; OR4: catalytic hydrogenationhydrogenation with wax oil; OR5: catalytic hydrogenation with gasolinegasoline and diesel; OR6: delayed coking; ST1: olefins olefins tank; ST2: gasoline tank; WT:WT: wastewaterwastewater treatment).treatment).

The top fivefive VOC species measured in each unit are list in Table 2 2,, andand thethe sourcesource profileprofile forfor petrochemical facilitiesfacilities asas a whole is compiled and introduced in Figure3 3.. InIn addition,addition, majormajor speciesspecies in thethe profileprofile and and their their percentage percentage in thein totalthe total mass mass are also are list also in thelist lastin the column last ofcolumn Table2 .of Generally, Table 2. C4–C6Generally, alkanes, C4–C6 propylene, alkanes, C6–C8propylene, aromatics, C6–C8 and aromatics, MTBE were and the MTBE major were composition the major for composition the petroleum for refinerythe . refineryn-Hexane industry. and iso-pentane n-Hexane wereand iso-pentane the most frequently were the monitored most frequently species inmonitored different processspecies in units different and accounted process units for a and large accounted part of the for total a large VOCs part emissions. of the total VOCs emissions. In detail, for OR1-OR3, n-Hexane was in the firstfirst grade with a range of 9.8–17.5%, followed by C4–C5 alkanes, alkanes, C6 C6 branched branched alkanes, alkanes, and and toluene. toluene. Catalytic Catalytic hydrogenation hydrogenation by wax by waxoil (OR4) oil (OR4) was wascharacterized characterized by high by high loadings loadings of aromatics of aromatics such such as toluene, as toluene, ethylbenzene ethylbenzene and and m/p-Xylene. m/p-Xylene. In Incompare, compare, aromatics aromatics were were negligible negligible in in OR5 OR5 unit unit whereas whereas C4–C6 C4–C6 nn--alkane were were the the most most significant. significant. For the the two two storage storage tanks, tanks, propylene propylene were were richest richest species species (21.0%), (21.0%), followed followed by C2–C4 by C2–C4 alkanes alkanes (5.9– 11.5%) in ST1 while C6 linear and branched alkanes were most abundant in ST2. Major species emitted from wastewater treatment were found to be C4–C6 linear alkanes.

Atmosphere 2018, 9, 297 7 of 18

(5.9–11.5%) in ST1 while C6 linear and branched alkanes were most abundant in ST2. Major species emitted from wastewater treatment were found to be C4–C6 linear alkanes. Atmosphere 2018, 9, x FOR PEER REVIEW 7 of 18 Table 2. The top five VOC species and their contributions to total VOC mass concentration measured inTable each 2. unit. The top five VOC species and their contributions to total VOC mass concentration measured in each unit. Species OR1 OR2 OR3 OR4 OR5 OR6 ST1 ST2 WT Whole Species OR1 OR2 OR3 OR4 OR5 OR6 ST1 ST2 WT Whole AlkanesAlkanes EthaneEthane 6.1% 6.1% 11.5%11.5% 3.8%3.8% PropanePropane 13.0%13.0% 3.6%3.6% i-Butanei-Butane 6.2% 6.2% 2.6% 2.6% n-Butanen-Butane 5.3% 5.3% 7.6% 5.9% 5.9% 7.0% 7.0% 3.7% 3.7% i-Pentanei-Pentane 5.6%5.6% 10.5%10.5% 6.0%6.0% 8.8% 7.0%7.0% 10.7%10.7% 6.5%6.5% n-Pentanen-Pentane 9.8% 9.8% 7.8% 11.0%11.0% 4.9%4.9% 2,3-Dimethylbutane2,3-Dimethylbutane 3.8%3.8% 1.2% 1.2% n-Hexanen-Hexane 9.8%9.8% 17.5%17.5% 12.9%12.9% 5.3% 28.7%28.7% 11.0% 11.0% 10.5% 10.5% 2-Methylpentane2-Methylpentane 5.3%5.3% 9.6% 9.6% 3.9% 3.9% 3-Methylpentane3-Methylpentane 4.9%4.9% 9.5%9.5% 7.6%7.6% 20.0%20.0% 6.2%6.2% MethylcyclopentaneMethylcyclopentane 7.9%7.9% 6.6%6.6% 12.7%12.7% 6.5%6.5% 5.4% 5.4% AlkenesAlkenes PropylenePropylene 13.5%13.5% 5.5% 21.0%21.0% 5.9%5.9% AromaticsAromatics TolueneToluene 9.6% 9.6% 5.9%5.9% 6.0%6.0% 3.6% 3.6% EthylbenzeneEthylbenzene 10.6%10.6% 9.1%9.1% 3.3% 3.3% m/p-Xylenem/p-Xylene 8.6%8.6% 5.4% 5.4% 2.9% 2.9% OVOCsOVOCs MTBEMTBE 19.0%19.0% 3.0%3.0%

FigureFigure 3. 3.VOCs VOCs sourcesource profile profile for for petrochemical petrochemical industry. industry.

VOCsVOCs fromfrom petrochemicalpetrochemical facilitiesfacilities werewere characterizedcharacterized byby previousprevious studiesstudies withwith aa focusfocus onon assessingassessing theirtheir impactimpact onon thethe environmentenvironment [23[23––2525].]. RecentRecent researchresearch hashas beenbeen devoteddevoted toto thethe establishmentestablishment of of the the source source profile profile of the of petrochemical the petrochemical industry industry and to identify and to specificidentify VOC specific emissions VOC originatingemissions fromoriginating the various from manufacturing the various manufacturing processes. Liu etprocesses. al. (2008) collectedLiu et al.seven (2008) ambient collected samples seven inambient a selected samples petrochemical in a selected industrial petrochemical area (PRD) industrial and reported area the (PRD) VOC and chemical reported structures the VOC of differentchemical oilstructures refinery sectionsof different [26 ].oil Mo refinery et al. (2015)sections investigated [26]. Mo et emission al. (2015) characteristics investigated emission of VOCs characteristics from various processof VOCs units from in various the petrochemical, process units basic in chemical,the petroc andhemical, chlorinated basic chemical, chemical and plants chlorinated in the YRD chemical region andplants compiled in the YRD the composite region and profiles compiled for eachthe composite sectors. The profiles top-10 for species each sectors. in the composite The top-10 profiles species of in petrochemicalthe composite in profiles this study of andpetrochemical their proportions in this in study other and studies their are proportions compared and in listedother instudies Figure are4. comparedMajor VOCand listed species in Figure for the 4. petrochemical industry measured in this study were similar to the profileMajor reported VOC by species Liu et for al. (2008),the petrochemical in which n-hexane industry was measured consistently in this the study most were abundant similar species to the inprofile both studies.reported However, by Liu et theal. (2008), levels ofin individualwhich n-hexane species was varied consistently across studies. the most The abundant proportions species of nin-pentane both studies. and toluene However, were the slightly levels lowerof individu than thatal species in the varied PRD region, across whilestudies. levels The ofproportions ethane and of propenen-pentane were and much toluene higher were in Wuhan slightly rather lower than than those thatfound in the in PRD the PRDregion, region. while In levels comparison, of ethane a clear and were much higher in Wuhan rather than those found in the PRD region. In comparison, a clear difference could be found between this study and results given by Mo et al. (2015). The chemical composition of VOCs in the YRD region exhibited a higher abundance of lighter components, especially ethane, propene, and n-butane, which were not obvious in Wuhan. Such discrepancy may be caused by different sampling locations in the petrochemical complex.

Atmosphere 2018, 9, 297 8 of 18 difference could be found between this study and results given by Mo et al. (2015). The chemical composition of VOCs in the YRD region exhibited a higher abundance of lighter components, especially ethane, propene, and n-butane, which were not obvious in Wuhan. Such discrepancy may be caused byAtmosphere different 2018 sampling, 9, x FOR PEER locations REVIEW in the petrochemical complex. 8 of 18

Figure 4. Comparison of major VOC species from the petrochemicalpetrochemical industry in different regions.

3.2. Surface Coat Coatinging and Printing According to Wuhan statistics, auto manufacturing is the leading source of surface coating in Wuhan, withwith vehiclevehicle productsproducts reached 1.768 million in 2016, yielding a 23.9% increase compared to 2015. TheThe completecomplete auto auto painting painting processes processes includes includes primer primer coating, coating, sealing sealing unit, intermediate unit, intermediate coating, andcoating, top coating.and top Primercoating. coating Primer aims coating to create aims anto create organic an binding organic layer binding to modify layer to the modify car surface the car in preparationsurface in preparation for subsequent for subsequent coating processes, coating followedprocesses, by followed under body by under coating body (UC) coating and stone (UC) guard and coatingstone guard (SGC) coating with sealing (SGC) materialwith sealing (mainly material consisting (mainly of PVC). consisting Intermediate of PVC). coating Intermediate was conducted coating betweenwas conducted primer between coating andprimer top coating coating, and the top latter coating, of which the is latter the last of which step in is the the auto last step coating in the process auto thatcoating is required process forthat final is required car aesthetics for final and car protection aesthetics toand add protection color, light to add refection, color, andlight waterproofing. refection, and Awaterproofing. detailed process A flowdetailed chart proc caness be foundflow chart elsewhere can [be27 ].found Measurements elsewhere demonstrated [27]. Measurements that the emissionsdemonstrated from that coating the emissions and baking from processes coating inand auto baking manufacturing processes in were auto significant manufacturing sources were to ambientsignificant VOCs sources [27]. to In ambient this study, VOCs samples [27]. In from this intermediatestudy, samples coating from intermediate were not collected coating because were not of thecollected difficulties because in sampling,of the difficulties while VOC in sampling, emissions while from VOC the other emissions major from process the units other were major measured process andunits studied. were measured and studied. As shown in Figure5 5,, emissionemission characteristicscharacteristics ofof thethe fourfour sectorssectors inin automobile automobile manufacturingmanufacturing workshops differed from each other. The possible reasons were the differences in raw and auxiliary materials used, manufacturing processes, and treatmenttreatment strategies. OVOCs were the largest group in EC1 and EC2, while aromatics were most abundant in EC3, reflectingreflecting the fact that both -based and oil-based may be used in the electro-coatingelectro-coating process. For the PVC sealing unit, aromatics dominate the chemical compositions of S1and S2, while S3 was characterized by high loadings of alkanes, alkenes, and alkyne. This is because S3 was collected at the funnel of the baking room where exhaust waswas collectedcollected andand treatedtreated by by catalytic catalytic combustion. combustion. Therefore, Therefore, VOC VOC compositions compositions measured measured in thisin this sample sample embodied embodied the the character character of of the the combustion combustion process, process, which which brokebroke downdown macromolecular organic chemical componentscomponents intointo smallersmaller molecules.molecules. Similarities Similarities in terms of VOC compositioncomposition patterns were observed in thethe top-coatingtop-coating sector (TC1–TC6), and aromatics were consistently the largest VOC VOC group group with with contributions contributions up up to to52.6–94. 52.6–94.6%6% of the of thetotal total mass mass weight. weight. RTO RTOfacilities facilities were wereequipped equipped in each in baking each baking room roomto collect to collect the exha theust exhaust after the after drying the dryingprocess. process. Among Among them RTO1– them RTO1–RTO4RTO4 were sampled were sampled at the funnel at the of funnel the baking of the un bakingits in unitsthe top in coating the top system. coating Therefore, system. Therefore, chemical structures of VOCs emitted from the RTO exhibited the combination of solvent use and combustion characters.

Atmosphere 2018, 9, 297 9 of 18 chemical structures of VOCs emitted from the RTO exhibited the combination of solvent use and combustionAtmosphere 2018 characters., 9, x FOR PEER REVIEW 9 of 18

Figure 5. Overall VOC chemical chemical group group patterns patterns of of four four major major sectors sectors in in auto auto manufacturing manufacturing industry. industry. (Note: EC1–EC3: electro-coating; S1–S3: sealing process; TC1–TC6: top coating).

Differences between emission compositions from top coating and those from other process units Differences between emission compositions from top coating and those from other process units were significant, and in consideration of sample’s representativeness, the profiles of six top coating were significant, and in consideration of sample’s representativeness, the profiles of six top coating samples were averaged into an integrated source profile to represent the average emission from auto samples were averaged into an integrated source profile to represent the average emission from auto coating industry. Figure 6 illustrates the source profile of the auto industry (Figure 6a) together with coating industry. Figure6 illustrates the source profile of the auto industry (Figure6a) together with chemical compositions of VOCs from surface-coating of air-conditioning (Figure 6b), gravure chemical compositions of VOCs from surface-coating of air-conditioning (Figure6b), gravure printing printing (Figure 6c), and offset printing (Figure 6d). (Figure6c), and offset printing (Figure6d). In general, aromatics (79.5~81.4%) were the largest group in auto-painting factories, while In general, aromatics (79.5~81.4%) were the largest group in auto-painting factories, oxygenated VOCs (82.0%) and heavy alkanes (68.7%) were dominant in gravure printing and offset while oxygenated VOCs (82.0%) and heavy alkanes (68.7%) were dominant in gravure printing printing factories, respectively. However, the major species of aromatic VOCs in the two surface and offset printing factories, respectively. However, the major species of aromatic VOCs in the two coating processes were different. C9 aromatics contributed a large part in the top-coating sector of surface coating processes were different. C9 aromatics contributed a large part in the top-coating sector the auto industry, with 1,2,4-trimethylbenzene being the top species with contributions of 27.5%. of the auto industry, with 1,2,4-trimethylbenzene being the top species with contributions of 27.5%. Instead, ethylbenzene, m/p-xylen,e and o-xylene were the major VOCs species in air-conditional Instead, ethylbenzene, m/p-xylen,e and o-xylene were the major VOCs species in air-conditional surface coating, with a combined contribution of 70.5% in the total, which were much lower in the surface coating, with a combined contribution of 70.5% in the total, which were much lower in the auto-coating sector. These discrepancies reflected that different raw materials in paints, thinners, and auto-coating sector. These discrepancies reflected that different raw materials in paints, thinners, were employed in the industry coating sectors. To further understand the local source and adhesives were employed in the industry coating sectors. To further understand the local source profile for auto coating, results in this study was compared with similar research in other regions, as profile for auto coating, results in this study was compared with similar research in other regions, shown in Figure 7. as shown in Figure7. The main species of VOCs differed remarkably between gravure printing and offset printing. The main species of VOCs differed remarkably between gravure printing and offset printing. For example, alkanes, especially heavy compounds (more than C7), namely methylcyclohexane, 2- For example, alkanes, especially heavy compounds (more than C7), namely methylcyclohexane, methylheptane, 3-methylheptane, and octane, exhibited high loadings in the source profile of offset 2-methylheptane, 3-methylheptane, and octane, exhibited high loadings in the source profile of printing, which accounted for 9.4%, 13.0%, 8.9%, and 22.3% of the total mass, respectively. In offset printing, which accounted for 9.4%, 13.0%, 8.9%, and 22.3% of the total mass, respectively. comparison, ethyl acetate and isopropanol were the highest contributing species in gravure printing, In comparison, ethyl acetate and isopropanol were the highest contributing species in gravure printing, accounting for 56.4% and 18.9% of the total VOCs. Since emissions from printing factories are mainly accounting for 56.4% and 18.9% of the total VOCs. Since emissions from printing factories are from evaporation, this observation reflected the fact that isopropanol was used solvent for mainly from ink evaporation, this observation reflected the fact that isopropanol was used solvent thinners in the gravure printing process. This finding was in agreement with the research by Zheng for thinners in the gravure printing process. This finding was in agreement with the research by et al. (2013) [9]. Zheng et al. (2013) [9].

Atmosphere 2018, 9, 297 10 of 18 Atmosphere 2018, 9, x FOR PEER REVIEW 10 of 18

FigureFigure 6. 6. VOCsVOCs source source profile profile for for surface surface coating coating and andprinting printing (a) auto (a) automanufacturing manufacturing (b) air- (b)conditional air-conditional industry industry (c) gravure (c) gravure printing printing (d) offset (d) offset printing. printing.

AllAll the the profiles profiles presented presented in the in literaturethe literature agree agree that aromatics that aromatics were consistently were consistently the largest the VOCs largest groupVOCs in group the automobile in the automobile coating industry, coating butindustry, the proportions but the proportions of individual of indi compoundsvidual compounds were different. were Therefore,different. to Therefore, better understand to better understand the local emission the local characteristics,emission characteristics, major aromatic major aromatic VOCs and VOCs their and contributionstheir contributions to the total to the emissions total emissions were compared were compared and are and illustrated are illustrated in Figure in7 .Figure 7. FigureFigure7 compared 7 compared the the main main aromatics aromatics species species measured measured in Wuhanin Wuhan with with those those reported reported in in BeijingBeijing [14 [14],], the the PRD PRD region region [9 ,[9,28],28], and and Shanghai Shanghai [29 [2].9]. The The auto auto coating coating source source profile profile witnessed witnessed the the significantsignificant improvement improvement of of raw raw materials materials used used in in the th painte paint coating coating practices. practices. Toluene, Toluene, ethylbenzene, ethylbenzene, m/p-xylene,m/p-xylene, and ando -xyleneo-xylene were were consistently consistently the the major major constituents constituents detected detected in in studies studies before before 2014. 2014. However,However, these these species species showed showed an an obvious obvious decrease, decrease, while while the the percentage percentage of of 1,2,4-trimethylbenzene 1,2,4-trimethylbenzene increasedincreased significantly. significantly. In In our our study,study, thethe coatingcoating profileprofile forfor WuhanWuhan had considerable amounts amounts of of1,2,4-trimethylbenzene 1,2,4-trimethylbenzene (27.5%), (27.5%), 1,2,3-trimethylbenzene 1,2,3-trimethylbenzene (8.3%), (8.3%), and andp-diethybenzenep-diethybenzene (7.0%), (7.0%), which whichwere were negligible negligible in previous in previous studies. studies. Similar Similar results results could could be found be found in the in PRD the PRDregion region in 2017, in 2017, where where1,2,4-trimethylbenzene 1,2,4-trimethylbenzene was wasthe second-largest the second-largest VOC VOC species species in the in auto the auto profile. profile. The Thedecreasing decreasing trend trendof toluene of toluene and and C8 C8aromatics, aromatics, whereas whereas the thegradually gradually increasing increasing of of1,2,4-trimethylbenzene 1,2,4-trimethylbenzene may may be a beresult a result of ofdifferent different paints paints and and solvent solvent formul formulationsations and standardsstandards promulgatedpromulgated byby the the local local governments.governments. Meanwhile, Meanwhile, these these changes changes indicated indicated that that VOCs VOCs emissions emissions source source profiles profiles need need to to be be updatedupdated and and localized. localized.

Atmosphere 2018, 9, 297 11 of 18 Atmosphere 2018, 9, x FOR PEER REVIEW 11 of 18

Atmosphere 2018, 9, x FOR PEER REVIEW 11 of 18

Figure 7. Comparison of major aromatics from auto coating in different regions. Figure 7. Comparison of major aromatics from auto coating in different regions. 3.3. Emissions from Electronics Manufacturing Industries 3.3. Emissions from Electronics Manufacturing Industries The electronicsFigure 7.industry, Comparison emitting of major 437,300 aromatics tons from VOCs auto in coating 2010, hasin different become regions. an important source Theof VOCs electronics in China industry, [30]. In addition emitting, VOCs 437,300 emitted tons by VOCsthe electronics in 2010, industry has become present an a importantsevere hazard source 3.3. Emissions from Electronics Manufacturing Industries of VOCsto both in the China environment [30]. In and addition, human VOCshealth [31]. emitted However, by the there electronics has been re industrylatively little present empirical a severe hazardresearch toThe both electronicsdevoted the environment to industry,investigating emitting and the human chemical437,300 health tons comp VOCs [ositions31]. in However, 2010, of VOCs has become thereemitted has anfrom important been the relativelyelectronics source little empiricalofmanufacturing VOCs research in China devotedprocess. [30]. In additionThis to investigating article, VOCs provides emitted the a chemicalbydetailed the electronics review compositions industryof VOCsof present that VOCs are a severe emittedemitted hazard from from the todifferent both the processes environment in the and electronics human healthindustry. [31]. To Ho bewever, specific, there six hassamples been coveredrelatively the little main empirical process electronics manufacturing process. This article provides a detailed review of VOCs that are emitted researchunits involved devoted in toVOCs investigating emissions the were chemical taken in comp a localositions printed of circuitVOCs emittedboards (PCB) from themanufacturing electronics frommanufacturing differententerprise. processes Meanwhile, process. in thethreeThis electronics articlesamples provides industry.were coll a detailedected To be in specific, reviewa semiconductor six of samplesVOCs thatmanufacturing covered are emitted the main factory from process unitsdifferentwhere involved integrated processes in VOCs circuits in emissionsthe electronics(IC) were were theindustry. taken main inproducts,To a be local specific, printedand onesix samples circuitsample boardsofcovered ambient (PCB) the air main manufacturingaround process the enterprise.unitsfactory involved Meanwhile, boundary in VOCs was three also emissions samples collected werewere as a taken background collected in a local in sample. a printed semiconductor circuit boards manufacturing (PCB) manufacturing factory where integratedenterprise.The circuits process Meanwhile, (IC) flow were charts three the of samples mainthe PCB products, wereand IC coll manufacturing andected one in a sample semiconductor are shown of ambient in Figuresmanufacturing air 8 around and 9, andfactory the the factory boundarywhereresults wasintegrated of VOCs also collected emissionscircuits (IC) as are a were backgroundillustrated the main in sample.Fiproducts,gure 10. andVOCs one emissions sample of from ambient PCB airmanufacturing around the factoryThemainly process boundaryproduced flow was in charts the also process ofcollected the PCBof asFilming anda background IC (inner manufacturing loop sample. formation), are shown liquid inphotoimageable Figures8 and 9solder, and the resultsmask ofThe VOCs(LPSM), process emissions test flow printing, charts are and of illustrated the weld PCB coating, and in IC Figure while manufacturing the10 .main VOCs emission are emissions shown section in Figures from in the PCB 8IC and industry manufacturing 9, and wasthe mainlyresultsthe produced lithography of VOCs in process theemissions process due are to of theillustrated Filming use of (innerphotoresist in Figure loop 10.and formation), VOCs organic emissions solvent liquid [31].from photoimageable PCB manufacturing solder mask mainly produced in the process of Filming (inner loop formation), liquid photoimageable solder (LPSM), test printing, and weld coating, while the main emission section in the IC industry was the mask (LPSM), test printing, and weld coating, while the main emission section in the IC industry was lithographythe lithography process process due to due the to use the of use photoresist of photoresist and and organic organic solvent solvent [31 [31].].

Figure 8. Process flow chart of a typical printed circuit board (PCB) manufacturing enterprise. (Note: CAM: Computer aided manufacturing; LPSM: liquid photoimageable solder mask).

FigureFigure 8. Process 8. Process flow flow chart chart of of a a typical typical printedprinted circui circuitt board board (PCB) (PCB) manufacturing manufacturing enterprise. enterprise. (Note: (Note: CAM: Computer aided manufacturing; LPSM: liquid photoimageable solder mask). CAM: Computer aided manufacturing; LPSM: liquid photoimageable solder mask).

Atmosphere 2018, 9, 297 12 of 18 Atmosphere 2018, 9, x FOR PEER REVIEW 12 of 18

Figure 9. Process flowflow chart of aa typicaltypical integratedintegrated circuitscircuits manufacturingmanufacturing enterprise.enterprise. (Note: CVD: chemical vapor deposition, Cu-BEol: copper wiring).

The results indicated that all these electronics manufacturing industries give middle or low The results indicated that all these electronics manufacturing industries give middle or low emissions, with total VOCs concentration less than 20 mg/m3 at each exhaust pipe, probably due to emissions, with total VOCs concentration less than 20 mg/m3 at each exhaust pipe, probably due to the VOCs released from this industry usually being at low concentrations but with a high flow rate. the VOCs released from this industry usually being at low concentrations but with a high flow rate. However, since the absolute value of VOC emissions may be affected by the sampling conditions, the However, since the absolute value of VOC emissions may be affected by the sampling conditions, chemical structure and the major individual species were studied to characterize the emission source, the chemical structure and the major individual species were studied to characterize the emission as shown in Figure 10 and Table 3. source, as shown in Figure 10 and Table3. There was a large difference in VOCs composition among the different sectors in PCB There was a large difference in VOCs composition among the different sectors in PCB manufacturing, while a similar composition of VOC emissions was observed for four units in IC manufacturing, while a similar composition of VOC emissions was observed for four units in industry. In case of the coating process in the filming sector of PCB manufacturing, OVOCs and IC industry. In case of the coating process in the filming sector of PCB manufacturing, OVOCs halocarbons dominated the chemical structure, with acetone being the largest contributing species and halocarbons dominated the chemical structure, with acetone being the largest contributing (13.3%), followed by ethyl acetate (12.8%) and dichloromethane (9.3%), as shown in Table 3. The species (13.3%), followed by ethyl acetate (12.8%) and dichloromethane (9.3%), as shown in Table3. composition of VOCs from the ink semi-cured process in the filming process was similar to that of The composition of VOCs from the ink semi-cured process in the filming process was similar to coating units, and acetone was consistently the most abundant species (28.5%), whereas 1,2- that of coating units, and acetone was consistently the most abundant species (28.5%), whereas dichloroethane was the second largest contributor, accounting for 11.7% to the total mass 1,2-dichloroethane was the second largest contributor, accounting for 11.7% to the total mass concentration. OVOCs emissions were much more significant form ink fully-cured process than that concentration. OVOCs emissions were much more significant form ink fully-cured process than in ink semi-cured unit because the high loading of acetone in this section, which contributed 62.4% that in ink semi-cured unit because the high loading of acetone in this section, which contributed of the total emissions. Variations can be observed among the composition of VOCs from text printing, 62.4% of the total emissions. Variations can be observed among the composition of VOCs from text circuit cleaning, and the filming process. For example, the alkanes’ contribution was higher in the printing, circuit cleaning, and the filming process. For example, the alkanes’ contribution was higher VOC emissions from text printing and circuit cleaning. Iso-pentane was one of the major species in the VOC emissions from text printing and circuit cleaning. Iso-pentane was one of the major species emitted from text printing sector except for acetone, 7.0% of the total, and may be used as a solvent emitted from text printing sector except for acetone, 7.0% of the total, and may be used as a solvent in in the printing process. I-Pentane and cyclohexane were the two largest contributing species in circuit the printing process. I-Pentane and cyclohexane were the two largest contributing species in circuit cleaning, accounting for 17.0% and 12.0%, respectively. For reflow soldering, the most important cleaning, accounting for 17.0% and 12.0%, respectively. For reflow soldering, the most important species were acetone (23.2%), acetylene (17.1%), and propane (6.3%), and the light hydrocarbons were species were acetone (23.2%), acetylene (17.1%), and propane (6.3%), and the light hydrocarbons were mainly attributable to the high temperature and combustion process. mainly attributable to the high temperature and combustion process. In terms of IC manufacturing, OVOCs provided the largest contribution to VOCs emitted from In terms of IC manufacturing, OVOCs provided the largest contribution to VOCs emitted from factory boundary and exhaust funnels after treating by rotary zeolite concentrating-incinerating factory boundary and exhaust funnels after treating by rotary zeolite concentrating-incinerating technology, accounting for 61.6–98.5% of the total mass. The most important OVOCs species were technology, accounting for 61.6–98.5% of the total mass. The most important OVOCs species were isopropanol (56.4–98.3%) and acetone (30.8%), while the others accounted for less than 20% of the isopropanol (56.4–98.3%) and acetone (30.8%), while the others accounted for less than 20% of the total total measured VOCs. measured VOCs.

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Figure 10. Overall VOC chemical group patterns of PCB and IC manufacturing (Note: RZC: exhaust Figure 10. Overall VOC chemical group patterns of PCB and IC manufacturing (Note: RZC: exhaust was treated by rotary zeolite concentrator). was treated by rotary zeolite concentrator).

Table 3. The top three VOC species and their percentage in total VOC mass concentration measured Table 3. The top three VOC species and their percentage in total VOC mass concentration measured in in each unit. each unit. Industry Sector TOP 1 TOP 2 TOP3 IndustryPCB Sector species TOP 1w% species TOP 2w% species TOP3 w% Filming-CoatingPCB speciesAcetone 13.3 w% Ethyl species acetate 12.8 w% Dichloromethane species 9.3 w% Filming-inkFilming-Coating semi cured Acetone Acetone 28.513.3 1,2-dichloroethaneEthyl acetate 11.712.8 DichloromethaneDichloromethane 6.6 9.3 Filming-inkFilming-ink semi fully cured cured Acetone Acetone 62.428.5 1,2-dichloroethaneIso-pentane 2.311.7 DichloromethaneAcrolein 1.9 6.6 Filming-inkText fullyprinting cured Acetone Acetone 15.362.4 Iso-pentaneIso-pentane 7.0 2.3 Isopropanol Acrolein 6.4 1.9 TextCircuit printing cleaning Iso-pentane Acetone 17.015.3 cyclohexaneIso-pentane 12.0 7.0 2,3-dimethylpentane Isopropanol 10.6 6.4 CircuitReflow cleaning soldering Iso-pentane Acetone 23.217.0 Acetylenecyclohexane 17.112.0 2,3-dimethylpentane Propane 6.3 10.6 Reflow solderingIC Acetone 23.2 Acetylene 17.1 Propane 6.3 FactoryIC boundary Isopropanol 56.4 Acetone 8.2 Ethane 6.4 Factory boundaryRZC1 IsopropanolIsopropanol 98.356.4 n-NonaneAcetone 0.3 8.2 Acetone Ethane 0.2 6.4 RZC1 Isopropanol 98.3 n-Nonane 0.3 Acetone 0.2 RZC1 Isopropanol 97.6 n-Nonane 0.8 Propene 0.4 RZC1 Isopropanol 97.6 n-Nonane 0.8 Propene 0.4 Incineration Acetone 30.8 Isopropanol 27.8 Ethene 14.5 Incineration Acetone 30.8 Isopropanol 27.8 Ethene 14.5

3.4. Gas Station Emissions 3.4. Gas Station Emissions Gasoline evaporation that occurs during refueling operations was thought to be the main Gasoline evaporation that occurs during refueling operations was thought to be the main pathway pathway of evaporative loss in China, while the other two pathways were headspace displacement of evaporative loss in China, while the other two pathways were headspace displacement from storage from storage tank and spillage/leakage in the course of loading and transportation [32]. Gasoline tank and spillage/leakage in the course of loading and transportation [32]. Gasoline vapors emitted vapors emitted when refueling cars in gas stations were measured in this study, and the results of when refueling cars in gas stations were measured in this study, and the results of group weight group weight percentages and individual chemical compositions of VOCs from gasoline and diesel percentages and individual chemical compositions of VOCs from gasoline and diesel evaporation are evaporation are illustrated in Figure 11. illustrated in Figure 11. It can be seen that chemical structures and composition profiles of VOCs emissions from It can be seen that chemical structures and composition profiles of VOCs emissions from gasoline gasoline 92# and 95# were almost identical. Alkanes were the dominant VOC group, with i-pentane 92# and 95# were almost identical. Alkanes were the dominant VOC group, with i-pentane being being the most abundant species (31.4–37.7%), followed by n-butane and n-pentane. Aromatics the most abundant species (31.4–37.7%), followed by n-butane and n-pentane. Aromatics accounted accounted for a small part (1.6–3.0%) in the vapor of gasoline 92# and 95#. This founding was similar for a small part (1.6–3.0%) in the vapor of gasoline 92# and 95#. This founding was similar to the to the research by Zhang 2013, who reported that aromatics were the main components in fuel [32] research by Zhang 2013, who reported that aromatics were the main components in fuel [32] and and took up high proportions in gasoline and diesel vehicle exhausts [33] but little in headspace took up high proportions in gasoline and diesel vehicle exhausts [33] but little in headspace vapors vapors and refueling emissions for their relative low vapor pressure [32,34]. VOC emissions from and refueling emissions for their relative low vapor pressure [32,34]. VOC emissions from gasoline gasoline 98# had slightly higher levels of n-butane and relatively lower loadings of i-pentane. However, the fractions of MTBE in vapor of gasoline 98# was distinctly higher than that in gasoline

Atmosphere 2018, 9, 297 14 of 18

98#Atmosphere had slightly 2018, 9, higher x FOR PEER levels REVIEW of n-butane and relatively lower loadings of i-pentane. However,14 the of 18 fractions of MTBE in vapor of gasoline 98# was distinctly higher than that in gasoline 92# and 95#, which92# and may 95#, be which attributed may to be differences attributed into differences the oil refinery in the process. oil refinery VOC process. composition VOC fromcomposition diesel fuel from evaporationdiesel fuel wasevaporation quite different was quite from di thatfferent of gasoline.from thatDiesel of gasoline. fuel had Diesel a higher fuel had abundance a higher of abundance heavier alkanes,of heavier especially alkanes, C6-C8 especially species C6-C8 such species as methylcyclohexane such as methylcyclohexane and n-heptane. and n-heptane. This founding This founding was a littlewas different a little different from the from observations the observations in Liu et in al. Liu (2008) et al. which (2008) reported which reported that heavier that heavier alkanes alkanes were consistentlywere consistently more abundant more abundant in diesel in vapor, diesel but vapor, the characteristic but the characteristic compounds compounds were major were >C8 major species, >C8 namely,species,n-nonane, namely,n -decane,n-nonane, and n-undecane.-decane, and This n discrepancy-undecane. reflectedThis discrepancy that the composition reflected ofthat VOCs the maycomposition change through of VOCs oil-upgrading may change campaigns. through oil-upgrading campaigns.

FigureFigure 11. 11.VOC VOC source source profile profile for gasolinefor gasoline and and diesel; diesel; (a) gasoline-92#; (a) gasoline-92#; (b) gasoline-95#; (b) gasoline-95#; (c) gasoline-98#; (c) gasoline- (d)98#; diesel-0#. (d) diesel-0#.

QualityQuality of of the the fuel fuel to to a largea large extent extent influences influence thes the engine engine efficiency efficiency and and exhaust exhaust emissions. emissions. Therefore,Therefore, upgrading upgrading fuel fuel quality quality to to lower lower vehicle vehicle emissions emissions is is crucial crucial to to improve improve air air quality quality in in China. China. SinceSince 2000, 2000, the the Chinese Chinese government government has has made made a greata great effort effort to to improve improve the the oil oil quality quality and and organized organized 5 times5 times oil oil upgrading upgrading campaigns campaigns to to promote promote the the emission emission legislation legislation vary vary from from China China I toI to China China V. V. EachEach campaign campaign was was accompanied accompanied with with more more strict strict emission emission standards standards on sulfur on sulfur and and olefins olefins in terms in terms of gasolineof gasoline and and higher higher requirement requirement on octaneon octane number number of diesel.of diesel. Wuhan Wuhan completed completed the the oil oil upgrading upgrading fromfrom China China IV IV to to China China V V during during this this study. study. As As noted noted above, above, source source profiles profiles associated associated with with gasoline gasoline evaporationevaporation may may vary vary from from the the oil oil quality quality and and emission emission standards, standards, and and results results in in the the present present study study werewere compared compared to to species species profiles profiles in in other other regions regions and an ind in different different stage stage of of emission emission legislations legislations with with thethe purpose purpose to to obtain obtain an an in-depth in-depth understanding understandin ofg of VOCs VOCs emissions emissions from from gasoline gasoline evaporation. evaporation. FigureFigure 12 12 shows shows the the top top 10 10 species species in in gasoline gasoline and and diesel diesel vapor vapor measured measured in in this this paper paper and and their their contributionscontributions in in previous previous studies. studies. In In termsterms ofof gasoline,gasoline, it can can be be found found that that all all these these profiles profiles show show the same three major compounds: n-butane, i-pentane, and n-pentane. However, fractions of these species were much more enriched in the gasoline vapor in accordance with China V (this study and Wang 2018) [35]. Instead, the percentage of toluene has been reduced gradually, from 9.5 wt % in PRD (China III) to 1.9 wt % in this study (China V). Source profiles data of diesel evaporation within

Atmosphere 2018, 9, 297 15 of 18 the same three major compounds: n-butane, i-pentane, and n-pentane. However, fractions of these species were much more enriched in the gasoline vapor in accordance with China V (this study and WangAtmosphere 2018) 2018 [35]., 9 Instead,, x FOR PEER the REVIEW percentage of toluene has been reduced gradually, from 9.5 wt % in PRD15 of 18 (China III) to 1.9 wt % in this study (China V). Source profiles data of diesel evaporation within last 10last years 10 were years hard were to hard obtain, to obtain, and only and two only sets two of sets composition of composition datawere data were available available and illustrated and illustrated in Figurein Figure 11b [ 3411b,35 [34,35].]. In the In casethe case of diesel of diesel refueling refueling emissions, emissions, the the percentage percentage of C4–C5of C4–C5 alkanes alkanes from from ourour study study were were much much higher higher than than that that reported reported by by Wang Wang et al.et al. (2018) (2018) measured measured in in Zhoushan Zhoushan City, City, andand He He et al.et al. (2015) (2015) investigated investigated in in Shanxi Shanxi Province. Province. It shouldIt should note note that thatn-undecane n-undecane was was the the most most abundantabundant species species in in the the source source profile profile of of diesel diesel vapor vapor measured measured by by He He etet al.,al., accountingaccounting for 49.2% of of the total mass.mass. TheThe greatgreat differencedifference maymay attributed attributed to to the the high high uncertainty uncertainty in in the the data data due due to to the the limitedlimited number number of samplesof samples tested. tested. Therefore, Therefore, more more work work is neededis needed in orderin order to generateto generate local local source source profilesprofiles that that are are more more representative. representative.

FigureFigure 12. 12.Top Top 10 VOCs10 VOCs species species in gasoline in gasoline and and diesel diesel vapor vapor and theirand their contributions contributions in other in other studies studies in differentin different regions regions and studying and studying periods, periods, (a) gasoline; (a) gasoline; (b) diesel. (b) diesel.

4. Conclusions4. Conclusions TheThe chemical chemical composition composition of majorof major VOCs VOCs anthropogenic anthropogenic sources sources in in Wuhan Wuhan were were experimentally experimentally measuredmeasured with with a focusa focus on on industrial industrial processes. processes. The The local local VOC VOC source source profiles profiles of theof the petrochemical petrochemical industry,industry, surface surface coating, coating, printing, printing, and and gasoline gasoline evaporation evaporation were were obtained obtained in in the the present present study. study. VOCsVOCs emitted emitted from from PCB PCB and and integrated integrated chip chip (IC) (IC) werewere alsoalso investigatedinvestigated but not averaged into into an anintegrated integrated source source profile profile due due to tothe the limit limit of samples of samples and and the great the great difference difference observed observed in each in process each processunit. unit. EmissionEmission compositions compositions from from the the petrochemical petrochemical industry industry were were much much more more complex complex than than those those fromfrom other other factories. factories. Alkanes Alkanes were were the the dominant dominant VOC VOC group group in allin all petrochemical petrochemical units, units, accounting accounting forfor 41.1–97.4% 41.1–97.4% of theof the total total VOCs VOCs mass mass concentration concentration with with an an average average fraction fraction of of 69.6%, 69.6%, followed followed by by aromatics (14.1%) and alkenes (9.9%). Major VOC species for the petrochemical industry measured in this study were similar to the profile reported by Liu et al. (2008), in that n-hexane was consistently the most abundant species in both cases. However, levels of individual species varied across studies. The source profile patterns were found to be similar from auto coating and equipment coating, with aromatics being the most abundant group. However, the characteristic species varied among processes due to the difference in raw materials and solvents used. C9 aromatics contributed a large

Atmosphere 2018, 9, 297 16 of 18 aromatics (14.1%) and alkenes (9.9%). Major VOC species for the petrochemical industry measured in this study were similar to the profile reported by Liu et al. (2008), in that n-hexane was consistently the most abundant species in both cases. However, levels of individual species varied across studies. The source profile patterns were found to be similar from auto coating and equipment coating, with aromatics being the most abundant group. However, the characteristic species varied among processes due to the difference in raw materials and solvents used. C9 aromatics contributed a large part in the auto industry, with 1,2,4-trimethylbenzene being the top species with contributions of 27.5%. Instead, ethylbenzene, m/p-xylene, and o-xylene were the major VOCs species in air-conditional surface coating. OVOCs (mainly ethyl acetate and isopropanol) dominated the profile of gravure printing, while heavy compounds (more than C7), namely methylcyclohexane, 2-methylheptane, 3-methylheptane, and octane, were the most abundant compounds emitted from offset printing. Acetone was the largest contributor and the most frequently monitored species in PCB manufacturing, while VOC species emitted from IC were characterized as high content of isopropanol (56.4–98.3%) and acetone (30.8%). In terms of gasoline evaporation, composition profiles of VOCs emissions from gasoline 92# and 95# were almost identical. Alkanes were the dominant VOC group, with i-pentane being the most abundant species (31.4–37.7%), followed by n-butane and n-pentane. VOCs emissions from gasoline 98# had slightly higher levels of n-butane and relatively lower loadings of i-pentane. However, the fractions of MTBE in vapor of gasoline 98# was distinctly higher than that in gasoline 92# and 95#. Diesel fuel had a higher abundance of heavier alkanes, especially C6-C8 species such as methylcyclohexane and n-heptane. Compared to similar studies in different stages of emission legislation, fractions of C4-C5 alkanes were much more enriched in the gasoline vapor in accordance with China V, while percentage of toluene has been reduced gradually, from 9.5 wt % in PRD (China III) to 1.9 wt % in this study (China V).

Supplementary Materials: Supplementary data to this article can be found online at http://www.mdpi.com/ 2073-4433/9/8/297/s1. Author Contributions: The work has been performed in collaboration among all the authors. L.S. designed the experiment, analyzed the data, and wrote the manuscript. Z.W. and S.L. (Sihua Lu) contributed to research design and paper reviewing and revising. S.L. (Shengwen Liang) took part in the source sampling and chemical analysis by GC–FID/MS. P.X., W.C. and M.W. worked on data analysis and the interpretation and discussion of the results. All authors agreed to submit this paper. Funding: This research was funded by the National Key R&D Program of China (2017YFC0212600) and The APC was funded by the special environmental research project of Hubei (project number 2014HB06). Acknowledgments: We are grateful for financial support from the National Key R&D Program of China (2017YFC0212600) and the special environmental research project of Hubei (project number 2014HB06). And we would like to show deep thankfulness to the editors who have contributed valuable comments to improve the quality of the paper. Conflicts of Interest: All authors declare that there is no conflict of interest.

References

1. Atkinson, R. Atmospheric chemistry of VOCs and NOx. Atmos. Environ. 2000, 34, 2063–2101. [CrossRef] 2. Kroll, J.H.; Ng, N.L.; Murphy, S.M.; Flagan, R.C.; Seinfeld, J.H. Secondary Organic Aerosol Formation from Isoprene Photooxidation. Environ. Sci. Technol. 2006, 40, 1869–1877. [CrossRef][PubMed] 3. An, T.; Huang, Y.; Li, G.; He, Z.; Chen, J.; Zhang, C. Pollution profiles and health risk assessment of VOCs emitted during e-waste dismantling processes associated with different dismantling methods. Environ. Int. 2014, 73, 186–194. [CrossRef][PubMed] 4. Wu, X.; Lu, Y.; Zhou, S.; Chen, L.; Xu, B. Impact of climate change on human infectious diseases: Empirical evidence and human adaptation. Environ. Int. 2016, 86, 14–23. [CrossRef][PubMed] 5. Guo, S.; Hu, M.; Zamora, M.L.; Peng, J.; Shang, D.; Zheng, J.; Du, Z.; Wu, Z.; Shao, M.; Zeng, L.; et al. Elucidating severe urban haze formation in China. Proc. Natl. Acad. Sci. USA 2014, 111, 17373–17378. [CrossRef][PubMed] Atmosphere 2018, 9, 297 17 of 18

6. Huang, R.J.; Zhang, Y.; Bozzetti, C.; Ho, K.F.; Cao, J.J.; Han, Y.; Daellenbach, K.R.; Slowik, J.G.; Platt, S.M.; Canonaco, F.; et al. High secondary aerosol contribution to particulate pollution during haze events in China. Nature 2014, 514, 218–222. [CrossRef][PubMed] 7. Mo, Z.; Shao, M.; Lu, S.; Qu, H.; Zhou, M.; Sun, J.; Gou, B. Process-specific emission characteristics of volatile organic compounds (VOCs) from petrochemical facilities in the Yangtze River Delta, China. Sci. Total Environ. 2015, 533, 422–431. [CrossRef][PubMed] 8. Shi, J.; Deng, H.; Bai, Z.; Kong, S.; Wang, X.; Hao, J.; Han, X.; Ning, P. Emission and profile characteristic of volatile organic compounds emitted from coke production, iron smelt, heating station and power plant in Liaoning Province, China. Sci. Total Environ. 2015, 515, 101–108. [CrossRef][PubMed] 9. Zheng, J.; Yu, Y.; Mo, Z.; Zhang, Z.; Wang, X.; Yin, S.; Peng, K.; Yang, Y.; Feng, X.; Cai, H. Industrial sector-based volatile organic compound (VOC) source profiles measured in manufacturing facilities in the Pearl River Delta, China. Sci. Total Environ. 2013, 456–457, 127–136. [CrossRef][PubMed] 10. Yao, Z.; Zhang, Y.; Shen, X.; Wang, X.; Wu, Y.; He, K. Impacts of temporary traffic control measures on vehicular emissions during the Asian Games in Guangzhou, China. J. Air Waste Manag. Assoc. 2012, 63, 11–19. [CrossRef] 11. Wang, H.-L.; Jing, S.-A.; Lou, S.-R.; Hu, Q.-Y.; Li, L.; Tao, S.-K.; Huang, C.; Qiao, L.-P.; Chen, C.-H. Volatile organic compounds (VOCs) source profiles of on-road vehicle emissions in China. Sci. Total Environ. 2017, 607–608, 253–261. 12. Na, K.; Kim, Y.P.; Moon, I.; Moon, K.C. Chemical composition of major VOC emission sources in the Seoul atmosphere. Chemosphere 2004, 55, 585–594. [CrossRef][PubMed] 13. Simon, H.; Beck, L.; Bhave, P.V.; Divita, F.; Hsu, Y.; Luecken, D.; Mobley, J.D.; Pouliot, G.A.; Reff, A.; Sarwar, G.; et al. The development and uses of EPA’s SPECIATE database. Atmos. Pollut. Res. 2010, 1, 196–206. [CrossRef] 14. Yuan, B.; Shao, M.; Lu, S.; Wang, B. Source profiles of volatile organic compounds associated with solvent use in Beijing, China. Atmos. Environ. 2010, 44, 1919–1926. [CrossRef] 15. Wei, W.; Wang, S.; Chatani, S.; Klimont, Z.; Cofala, J.; Hao, J. Emission and speciation of non- volatile organic compounds from anthropogenic sources in China. Atmos. Environ. 2008, 42, 4976–4988. [CrossRef] 16. Huang, C.; Chen, C.H.; Li, L.; Cheng, Z.; Wang, H.L.; Huang, H.Y.; Streets, D.G.; Wang, Y.J.; Zhang, G.F.; Chen, Y.R. Emission inventory of anthropogenic air pollutants and VOC species in the Yangtze River Delta region, China. Atmos. Chem. Phys. 2011, 11, 4105–4120. [CrossRef] 17. Ou, J.; Zheng, J.; Li, R.; Huang, X.; Zhong, Z.; Zhong, L.; Lin, H. Speciated OVOC and VOC emission inventories and their implications for reactivity-based ozone control strategy in the Pearl River Delta region, China. Sci. Total Environ. 2015, 530–531, 393–402. [CrossRef][PubMed] 18. Lyu, X.P.; Chen, N.; Guo, H.; Zhang, W.H.; Wang, N.; Wang, Y.; Liu, M. Ambient volatile organic compounds and their effect on ozone production in Wuhan, central China. Sci. Total Environ. 2016, 541, 200–209. [CrossRef][PubMed] 19. Kalabokas, P.D.; Hatzianestis, J.; Bartzis, J.G.; Papagiannakopoulos, P. Atmospheric concentrations of saturated and aromatic hydrocarbons around a Greek oil refinery. Atmos. Environ. 2001, 35, 2545–2555. [CrossRef] 20. Chen, C.-L.; Fang, H.Y.; Shu, C.-M. Source Location and Characterization of Volatile Organic Compound Emissions at a Petrochemical Plant in Kaohsiung, Taiwan. J. Air Waste Manag. Assoc. 2012, 55, 1487–1497. [CrossRef] 21. Yen, C.H.; Horng, J.J. Volatile organic compounds (VOCs) emission characteristics and control strategies for a petrochemical industrial area in middle Taiwan. J. Environ. Sci. Health. Part A Toxic/Hazard. Subst. Environ. Eng. 2009, 44, 1424–1429. [CrossRef][PubMed] 22. Liu, Y.; Shao, M.; Zhang, J.; Fu, L.; Lu, S. Distributions and source apportionment of ambient volatile organic compounds in Beijing city, China. J. Environ. Sci. Health. Part A Toxic/Hazard. Subst. Environ. Eng. 2005, 40, 1843–1860. [CrossRef][PubMed] 23. Cetin, E.; Odabasi, M.; Seyfioglu, R. Ambient volatile organic compound (VOC) concentrations around a petrochemical complex and a petroleum refinery. Sci. Total Environ. 2003, 312, 103–112. [CrossRef] 24. Lin, T.-Y.; Sree, U.; Tseng, S.-H.; Chiu, K.H.; Wu, C.-H.; Lo, J.-G. Volatile organic compound concentrations in ambient air of Kaohsiung petroleum refinery in Taiwan. Atmos. Environ. 2004, 38, 4111–4122. [CrossRef] Atmosphere 2018, 9, 297 18 of 18

25. Ras, M.R.; Marce, R.M.; Borrull, F. Characterization of ozone precursor volatile organic compounds in urban atmospheres and around the petrochemical industry in the Tarragona region. Sci. Total Environ. 2009, 407, 4312–4319. [CrossRef][PubMed] 26. Liu, Y.; Shao, M.; Fu, L.; Lu, S.; Zeng, L.; Tang, D. Source profiles of volatile organic compounds (VOCs) measured in China: Part I. Atmos. Environ. 2008, 42, 6247–6260. [CrossRef] 27. Wang, H.; Nie, L.; Li, J.; Wang, Y.; Wang, G.; Wang, J.; Hao, Z. Characterization and assessment of volatile organic compounds (VOCs) emissions from typical industries. Chin. Sci. Bull. 2013, 58, 724–730. [CrossRef] 28. Zhong, Z.; Sha, Q.; Zheng, J.; Yuan, Z.; Gao, Z.; Ou, J.; Zheng, Z.; Li, C.; Huang, Z. Sector-based VOCs emission factors and source profiles for the surface coating industry in the Pearl River Delta region of China. Sci. Total Environ. 2017, 583, 19–28. [CrossRef][PubMed] 29. Wang, H. Source Profiles and Chemical Reactivity of Volatile Organic Compounds from Solvent Use in Shanghai, China. Aerosol Air Qual. Res. 2014, 14, 301–310. [CrossRef] 30. Qiu, K.; Yang, L.; Lin, J.; Wang, P.; Yang, Y.; Ye, D.; Wang, L. Historical industrial emissions of non-methane volatile organic compounds in China for the period of 1980–2010. Atmos. Environ. 2014, 86, 102–112. [CrossRef] 31. Babar, Z.B.; Shareefdeen, Z. Management and control of air emissions from electronic industries. Clean Technol. Environ. Policy 2013, 16, 69–77. [CrossRef] 32. Zhang, Y.; Wang, X.; Zhang, Z.; Lü, S.; Shao, M.; Lee, F.S.C.; Yu, J. Species profiles and normalized reactivity of volatile organic compounds from gasoline evaporation in China. Atmos. Environ. 2013, 79, 110–118. [CrossRef] 33. Guo, H.; Zou, S.C.; Tsai, W.Y.; Chan, L.Y.; Blake, D.R. Emission characteristics of nonmethane hydrocarbons from private cars and taxis at different driving speeds in Hong Kong. Atmos. Environ. 2011, 45, 2711–2721. [CrossRef] 34. He, Q.; Yan, Y.; Li, H.; Zhang, Y.; Chen, L.; Wang, Y. Characteristics and reactivity of volatile organic compounds from non- emission sources in China. Atmos. Environ. 2015, 115, 153–162. [CrossRef] 35. Wang, Q.; Li, S.; Dong, M.; Li, W.; Gao, X.; Ye, R.; Zhang, D. VOCs emission characteristics and priority control analysis based on VOCs emission inventories and ozone formation potentials in Zhoushan. Atmos. Environ. 2018, 182, 234–241. [CrossRef]

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