Science of the Total Environment 745 (2020) 140838

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Improved emissions inventory and VOCs speciation for industrial OFPestimation in China

Xiaoming Liang a,b,⁎, Xibo Sun c, Jiantie Xu a, Daiqi Ye a,⁎⁎a School of Environment and Energy, South China University of Technology, Guangzhou 510006, Chinab State Environmental Protection Key Laboratory of Urban Ecological Environment Simulation and Protection, South China Institute of Environmental Science,Ministry of Ecology and Environment,Guangzhou 510655, Chinac Guangdong Provincial Academy of Environmental Science, Guangzhou 510045, China

H I G H L I G H T S G R A P H I C A L A B S T R A C T

• Improved industrial VOCs emissions in-ventories for China from 2011 to 2018were developed.

• Annual growth rate for VOCs emissionshad two different growth stages.

• Speciated and OFP-based VOCs emis-sions inventories for 2018 were com-piled.

• Species and source characteristics interms of emissions and OFP were differ-ent.

• Top 20 species and top 10 sources interms of OFP were identified.

⁎ Correspondence to: X. Liang, South China Institute of Eof Ecology and Environment, Guangzhou 510655, China.⁎⁎ Corresponding author.

E-mail addresses: liangxiaoming@scies.org (X. Liang),

https://doi.org/10.1016/j.scitotenv.2020.1408380048-9697/© 2020 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 22 April 2020Received in revised form 5 July 2020Accepted 7 July 2020Available online 13 July 2020

Editor: Jianmin Chen

Keywords:VOCsSource profilesSpeciated emissions inventoryOzoneOFP

Ozone (O3) pollution is becoming increasingly serious in China. Reactivity-based control of volatile organic com-pounds (VOCs) is an efficientmethod of alleviating O3 pollution. In this study, an improved industrial VOCs emis-sions inventory for China from2011 to 2018 and local source profiles for six specific industrieswere developed toimprove estimation of ozone formation potential (OFP). The results indicated that average annual growth rate forindustrial VOCs emissions during 2015–2018 was lower than 2011–2014, which could be related to China's in-dustrial structural upgrade and implementation of VOCs source control during the 13th Five-Year Plan period.The industrial coating, printing, basic organic chemical, gasoline storage and transport, and oil refinery industrieswere the key sources of VOCs emissions. M/p-xylene, toluene, ethyl benzene, propene, o-xylene, ethene, 1,2,4-trimethylbenzene, m-ethyl toluene, isopentane, and 1-butene were the top 10 species in terms of OFP. The top20 species based on OFP accounted for an estimated 85% of total OFP and only 59% of emissions. The industrialcoating, printing, basic organic chemical, oil refinery industries and other five sectors were the top 10 sourcesin terms of OFP, which together contributed 81% of total OFP. Priority should be given to the top 20 or more spe-cies with high reactivity and the top 10 sources based on OFP for future O3 reductions in China.

© 2020 Elsevier B.V. All rights reserved.

nvironmental Science,Ministry

cedqye@scut.edu.cn (D. Ye).

1. Introduction

Pollution with high near-surface concentrations of ozone (O3) andsecondary organic aerosols (SOA) occurs frequently in China (Shaoet al., 2009; Guo et al., 2014; Xue et al., 2014). Under the National Air

Table 1Sampling locations and numbers of field measurements taken.

Source type Sampling location No. ofsamples

Vegetable oil industry Leaching process units of rapeseedprocessingRapeseed oil storage tank area

3

Beer industry Beer fermentation unitsProduct storage areaSewage treatment

4

Paper products industry Pulp manufacturing workshopDrying processSewage treatment

5

Gravure printing Stack gasPrinting process

4

Flexible packagingbonding

Stack gasBonding process

4

Wood processing industry Rubber workshopHot pressing process

3

Total 23

2 X. Liang et al. / Science of the Total Environment 745 (2020) 140838

Pollution Prevention and Control Action Plan, implemented in 2013 (MEE,2019), great effort has been made to reduce this pollution. As a result,average annual concentrations of PM2.5 in the Beijing-Tianjin-Hebei,Yangtze River Delta (YRD) and Pearl River Delta (PRD) regions were re-duced by 48%, 39%, and 32%, respectively, in 2018 compared to 2013.Nonetheless, the 8 h O3 level in China continued to increase, from139mg/m3 in 2013 to 151mg/m3 in 2018 (MEE, 2014, 2019). Accordingto a report on the environmental state of Guangdong province, the per-centage of days with PM2.5 as the primary pollutant in PRD decreasedfrom 46% in 2013 to 17% in 2018. By contrast, the percentage of dayswith O3 as the primary pollutant increased from 27% to 56% over thissame period (GDDEE, 2014, 2019).

Volatile organic compounds (VOCs) are crucial precursors to the for-mation of O3 and PM2.5 (Hao, 2012; Yuan et al., 2013; Zhao et al., 2013).Observations of ambient O3 and its precursors show that major devel-oped areas that do not attain O3 standards are sensitive to VOCs, includ-ing the Beijing-Tianjin area, YRD, and PRD (Ran et al., 2009; Tang et al.,2012; Ding et al., 2013; Han et al., 2013; Lam et al., 2013). Therefore, ef-fectively controlling VOCs emissions is essential to alleviating O3 pollu-tion in China. In several developed countries, controlling specific VOCsspecies based on their reactivity in O3 formation has been effective(CARB, 2000; Stoeckenius and Russell, 2005; US EPA, 2005; Derwentet al., 2007). In China, the reactivity-based approach to controllinghighly reactive VOCs is more effective than the traditional mass-basedapproach (Ou et al., 2015; Liang et al., 2017a, 2017b; Wu and Xie,2017; Wang et al., 2018).

Speciated VOCs emissions and the estimation of ozone formation po-tential (OFP) are essential to the reactivity-based control approach. Al-though mass-based measures of controlling VOCs are widespread inChina, many efforts have been made to characterize emissions ofspeciated VOCs in a certain year or a long period for China (Wei et al.,2008, 2014; Li et al., 2014, 2019; Niu et al., 2016; Liang et al., 2017a,2017b; Wu and Xie, 2017; Zhao et al., 2017). However, most of the na-tional inventories were based largely on old or foreign emissions factorsand sources profiles (Wuet al., 2016;WuandXie, 2017). For Chinese in-dustrial sources, Liang et al. (2017a, 2017b) used a reactivity-based con-trol approach based on a 2010 industrial emissions inventory (Qiu et al.,2014) for OFP-based characterization of VOCs. Although they madeprogress, several challenges remain. First, some important sources of in-dustrial manufacturing and solvent usage (e.g., the basic organic chem-ical, electronics, and metal smelting industries) were absent from the2010 emissions inventory (Qiu et al., 2014). Second, many emissionsfactors included in the inventory were outdated (e.g., the oil refinery,printing, industrial coating, shoemaking, and synthetic leather indus-tries). Emissions data from developed countries (e.g., the EPA AP-42 da-tabase) also do not reflect current VOCs emissions in China. Third, manysource profiles used for speciation analyses had been collected in previ-ous years (e.g., the profiles for storage and transportationwere from be-fore 2008) or from the widely used EPA SPECIATE database (e.g., thewood processing, paper products, vegetable oil, and beer production in-dustries). These shortcomings may compromise the accuracy of the es-timation of speciated VOCs emissions in China. Finally, as a result ofrapid economic development, industrial structural upgrades, and imple-mentation of VOCs source controls, VOCs emissions characteristics arechanging constantly. Therefore, the development of a VOCs emissionsand speciation inventory and the estimation of industrial OFP to supportreactivity-based O3 control strategies in China are essential.

The objectives of this work aremainly included as follows: (1) to es-tablish local source profiles related to six specific industries in China;(2) to improve industrial VOCs emissions inventories for China from2011 to 2018 using recent emissions factors; (3) to compile industrialspeciated VOCs emissions inventories based on the newly establishedlocal source profiles; (4) to estimate industrial OFP based on maximumincremental reactivity (MIR). The results of this study will be useful forgovernments developing efficient reactivity-based O3 control strategiesand improving VOCs control in China.

2. Methodology

2.1. Sampling and analyses of VOCs

Chemical profiles are crucial for the creation of a speciated VOCsemissions inventory. Six specific industrial sources were selected tomeasure the chemical composition of VOCs emissions in Guangdongprovince, a region in South China with a rich industrial sector andhigh VOCs emissions, including the vegetable oil, beer, paper products,gravure printing, flexible packaging bonding, and wood processing in-dustries. Data on chemical composition for the vegetable oil, beer, andpaper products industries are still lacking in China, as these industriesare not currently major sources of VOCs in China. For the gravure print-ing, flexible packaging bonding, and wood processing industries, pro-files are not sufficiently refined because of the variability in thesesources. Therefore, the current work is expected to supplement sourceprofiles for industrial sources in China. Using onsite investigations ofmajor emissions processes, we determined the locations of stacks andfugitive emissions for each source type. Detailed information aboutthe sampling sites is presented in Table 1.

Stack and fugitive emissions samples from each source were col-lected in 6 L summa canisters. Stack emissions samples were obtainedfrom exhaust funnels after control equipment under normal operatingconditions. Parallel samples were taken at an interval of 1 h. A total of23 samples were obtained from six industrial sources. Three sampleswere taken from a vegetable oilmanufacturingplant: two from leachingprocess units used for rapeseed processing and one from a rapeseed oilstorage tank area. Four fugitive emissions sampleswere obtained fromabeer factory: two of exhaust from beer fermentation units, one from aproduct storage area, and one of exhaust from sewage treatment. Fivefugitive emissions samples were collected in a paper productsmanufacturing factory: two from the pulp manufacturing workshop,two from the drying workshop, and one from sewage treatment. Twostack emissions and two fugitive emissions samples were taken fromgravure printing and flexible packaging bonding factories, respectively.Three fugitive emissions samples were obtained from a wood process-ing facility: one from a rubberized workshop and two from a hot press-ing workshop.

VOCs samples were analyzed according to the EPA TO-15 methodwith gas chromatography–mass spectrometry (GC–MS; Agilent 7890A/5975C, USA). Briefly, each sample was pumped into a preconcentratorwith a three-stage trapping system (Model 7100, Entech Instruments,USA). In the first stage, VOCs were adsorbed on glass beads at−160 °Cand desorbed at 10 °C.Water vapor was converted into solid ice and sep-arated from the sample. In the second stage, the sample was trapped on

3X. Liang et al. / Science of the Total Environment 745 (2020) 140838

Tenax at −30 °C and desorbed at 180 °C to separate the target speciesfrom CO2 and other components of air. In the third stage, the samplewas focused into a transfer line at −160 °C and heated rapidly to 70 °C,concentrating the target species. The concentrated VOCs were injectedinto the gas chromatograph (GC). The GC oven temperature was set ini-tially to 35 °C, increased to 120 °C at 5 °C min−1 and to 250 °C at10 °C min−1, and then held for 10 min. An HP-1 capillary column(60 m × 0.32mm× 1.0 μm; Agilent Technologies, USA) was used to sep-arate themixture. Themass spectrometerwas operated in scanmode andscanned 20–42 and 35–300 amu before and after 8.5 min, respectively.The ionization method was electron impacting, and the source tempera-ture was 230 °C. The Photochemical Assessment Monitoring Station(PAMS; 57 compounds) and TO-15 (25 compounds) standard mixtureswere used to confirm the retention times of various compounds to sup-port the identification of compounds based on retention time and massspectrum. For quality assurance, a laboratory blank samplewas processedevery 10 samples following the same procedure used for real samples,and no detectable VOCs were present. The field blanks were tested, andno significant contamination was found. The analyzed data were consid-ered reliable if the correlation between parallel samples was greater than0.9. The concentrations of parallel samples were averaged and furthernormalized to mass percentages. The limits of detection were below0.1 μg m−3 for all species.

2.2. Compilation of the emissions inventory

2.2.1. Classification of sourcesIn compiling the VOCs emissions inventory, we used typical in-

dustrial source classification based on the source-tracing method(Qiu et al., 2014) to trace the material flow of VOCs associated witheach industrial process. Industrial sources were divided into four cat-egories: production of VOCs, storage and transport, industrial pro-cesses using VOCs as raw materials, and processes using VOCs-containing products.

Compared to the VOCs sources for the period 1989–2010 reported inour previous work (Qiu et al., 2014), a few important improvementswere made. First, some previously missing sources were incorporated,including the basic organic chemical (e.g., acrylic, acetic acid, ethyl ace-tate, formaldehyde and butadiene production); electronicsmanufactur-ing (e.g., enameled wire, printed circuit boards, aluminum electrolyticcapacitors, and IC production); metal smelting (e.g., nickel, aluminum,magnesium, and zinc smelting); and fertilizer, dye, pigment, and ce-ment manufacturing industries. Second, some non-industrial sourceswere eliminated from the new system. For example, architectural deco-ration and dry cleaning are better suited to the category of domesticsources in China. Third, some important sources were reclassifiedbased on new industrial and activity data. For example, the furnituremanufacturing industry and the machinery and transport equipmentindustry were reclassified as the industrial coating industry, includingthewood products, automobile manufacturing and repair, shipbuilding,and industrial protective coating industries. As a result, a total of 96sources encompassing nearly all industrial emissions sources werecomprehensively considered.

2.2.2. Emissions estimationWe calculated VOCs emissions from industrial sources in China dur-

ing the period 2011–2018 using Eq. (1):

E yð Þ ¼X

i

A i; yð Þ � EF i; yð Þ ð1Þ

where i is the specific source; y is the year; E is the annual emissions;A is the activity data (i.e., the consumption of raw material orquantities of products); and EF is the emissions factor(i.e., emissions per unit of A).

We then broke down total industrial VOCs emissions in 2018 for agiven source type into individual species for the speciated VOC emis-sions inventory using Eq. (2):

E jð Þ ¼X

i

E ið Þ � R i; jð Þ ð2Þ

where j is a specific VOCs species; E(j) is the total emissions of the spe-cies j; E(i) is the total emissions of the source i, and R(i, j) is the ratio ofspecies j to source i.

2.2.3. Emissions factorsWhen evaluating emissions factors, we gave priority to the most re-

cent emissions factors obtained directly through domestic emissionsmeasurements and source investigations in China to reduce uncertaintyin the emissions inventory. Emissions factors for printing, industrialcoating, and electronics manufacturing sources were reevaluated.These emissions factors were developed based on our recent investiga-tion (Liang et al., 2019) and emissions control status in China. For exam-ple, the emissions factor for offset printing was reestimated based on60% solvent-based and 40%water-based ink,with 20% terminal effectivetreatment and 80% ineffective treatment. In addition, newly obtainedemissions factors for some crucial sources (e.g., the oil refinery, automo-bile manufacturing and repair, shoemaking, and synthetic leather in-dustries) were adopted. The emissions factors for these crucial sourceswere developed based on recent local field emissions investigations ofthe relevant industries (Xu et al., 2016; Lu, 2017; Xu et al., 2019; Tenget al., 2020). Details of the emissions factors used in this study are listedin Table S1.

2.2.4. Activity dataMost source-specific activity data used in this study were obtained

from themost up-to-date sources, such as the China Statistical Yearbook(2011–2018), China Energy Statistical Yearbook (2011–2018), and re-ports from various industry associations (e.g., the China Adhesives andTape Industry Association). Some data were obtained only at the na-tional scale, such as dye consumption by the textile printing industryand adhesive consumption by the wood processing industry. We ex-trapolated these national activity levels to the province level by multi-plying the national data with the relative percentages of industryproduction, such as printed and dyed cloth production and woodpanel production. Data on the consumption of solvents (e.g., paint,ink, and adhesive) for specific industries were often not subdivided bytype. Statistical data should be applied to these values before use. Forexample, ink consumption was allocated to offset printing, gravureprinting, screen printing, flexo printing, ultraviolet printing, and otherareas according to the ink production proportion of each subsector.

2.2.5. Source profilesWeused themost recent data fromChina and themeasurements ob-

tained in this study to compile the VOCs source profiles database. Basedon the 2010 VOCs source profiles database described in our previouswork (Liang et al., 2017a, 2017b), several important data were addedto the new database. For example, source profiles were added for thegravure printing, flexible packaging bonding, wood processing, paperproducts, vegetable oil, and beer industries. In our previous work(Liang et al., 2017a, 2017b), most of these source profiles followed theUS EPA SPECIATE 4.4 database (US EPA, 2015) and did not reflect thecharacteristics of VOCs in China. In addition, newly obtained source pro-files for crude oil, gasoline, and diesel storage and transport (Wang et al.,2018), acetate fiber and synthetic rubber production (Zhao et al., 2017),automobile manufacturing (Shen et al., 2018), fertilizer manufacturing;and textile printing, enameled wire manufacturing, and wastewatertreatment (Wu and Xie, 2017) were used in this study. These sourceprofiles were established based on the most recent local field measure-ments available for the relevant industries. Detailed chemical profiles of

4 X. Liang et al. / Science of the Total Environment 745 (2020) 140838

each emissions source are summarized in Table S2 in the SupplementalMaterials.

2.3. Analyses of O3 formation

2.3.1. OFP emissions intensity (OFPEI)Similar to the emissions factor for mass, OFPEI quantitatively charac-

terizes the OFP emissions intensity or reactivity per unit emissions ofeach source. The OFPEI of each source was calculated as follows:

OFPEI ið Þ ¼X

j

R i; jð Þ �MIR jð Þ ð3Þ

where OFPEI(i) is the OFP emissions intensity of the source i; MIR(j) ismaximum incremental reactivity of the species j. The updated MIRvalues reported by Carter (2010) were used in this study.

2.3.2. OFP emissions inventoryAn OFP-based VOCs emissions inventory was compiled based on the

emissions inventory by mass for each source and its correspondingOFPEI as well as speciated VOCs emissions inventory and MIR values.We calculated total industrial OFP using Eq. (4) or Eq. (5):

OFPI ¼X

i

OFPEI ið Þ � E ið Þ ð4Þ

OFP J ¼X

j

MIR jð Þ � E jð Þ ð5Þ

where the OFPI and OFPJ are total OFP emissions of industrial sources inChina calculated on the basis of source emission inventory andspeciated emissions inventory, respectively.

3. Results and discussion

3.1. Source profiles based on measurement

VOCs source profiles of six specific industrial sources—the vegetableoil, beer, paper products, gravure printing, flexible packaging bonding,and wood processing industries—were obtained from local measure-ments collected in China. The chemical components of 82 species de-tected with GC–MS were divided into six groups, namely, alkanes,alkenes/alkynes, aromatic hydrocarbons, halocarbons, oxygenated or-ganics, and others, as illustrated in Fig. 1. The detailed VOCs chemical

0%

20%

40%

60%

80%

100%

VOI BI PI GP

Mas

s fr

acti

on

Fig. 1. VOCs source profiles measured in specific industrial sources, grouped by species. VOI, Bflexible packaging bonding, and wood processing industries, respectively.

compositions of these six industrial sources are summarized inTable S2 in the Supplemental Materials.

Alkanes were the main species released from the vegetable oil in-dustry, withmass fractions close to 80%.N-hexane, an alkane commonlyused in the extraction of vegetable oil, was the largest contributor, ac-counting for 50% of total mass, followed by 3-methyl pentane (11%),n-propane (3.7%), methyl isobutyl ketone (3.7%), and 1,4-dioxane(3.6%). In the beer industry, alkanes and oxygenated VOCs (OVOCs)were themain species, withmass fractions of 46% and 29%, respectively.Isopropyl alcohol (23%), isopentane (19%), n-pentane (7%), acetylene(7%), and 3-methyl heptane (6%) were the top five species associatedwith the beer industry. Similar to the source profiles for wine produc-tion in the EPA SPECIATE database, isopropyl alcohol was identified asthe dominant species. For the paper products industry, alkanes andOVOCs were also the main species. N-butane, n-propane, methylisobutyl ketone, 1,4-dioxane, and ethyl acetate were the main species,accounting for 50% in total. In the gravure printing and flexible packag-ing bonding industries, OVOCs contributed the largest mass fractions,reaching 52% and 41%, respectively. A raw material or thinner used inprinting inks and adhesives, ethyl acetate was the main species forthose industries, accounting for 43% and 29%, respectively. In thewood processing industry, alkanes were the main chemical groups re-leased, with a measured mass fraction of 56%. Isopentane (24%), n-decane (10%), n-pentane (5.7%), propene (4.9%), and 1-butene (4.8%)were the top five species. Note that some important species linked tothe wood processing industry, such as formaldehyde, were not mea-sured in this work because of limitations of our testing methods.

3.2. Sectoral contributions and interannual trends of VOCs emissions

Total industrial VOCs emissions in China in 2018 reached 12,446 kt.As shown in Fig. 2, the source category of processes using VOCs-containing products was the largest contributor, accounting for 58% ofthe total industrial VOCs emissions, followed by industrial processesusing VOCs as raw materials, storage and transport, and production ofVOCs, with contributions of 17%, 13% and 12%, respectively. In the pro-cesses using VOCs-containing products category, the industrial coatingand printing industries were the largest emitters, accounting for 48%and 19%, respectively. The protective coating andwood products indus-tries contributed 31% and 10%, of total VOCs emissions for the industrialcoating industry. Flexible packaging bonding (13%)was the largest con-tributor to emissions from the printing industry. In the category of in-dustrial processes using VOCs as raw materials, food and drinkprocessing (24%), paints and similar products (19%), pharmaceutical

FPB WI

Alkanes

Alkenes/Alkynes

Aromatics

Halocarbons

OVOCs

Others

I, PI, GP, FPB, and WI represent the vegetable oil, beer, paper products, gravure printing,

Fig. 2. Contributions by sector to industrial VOCs emissions in four source categories in China in 2018.

5X. Liang et al. / Science of the Total Environment 745 (2020) 140838

(16%), synthetic fiber (15%) and rubber products (11%) were the topfive industries. For storage and transport, gasoline, crude oil and dieselmade up 41%, 31%, and 28% of the total, respectively. The basic organicchemical industry (48%) and oil refinery industry (41%) were the toptwo emissions sources in the production of VOCs category. Industrialcoating, printing, basic organic chemical, gasoline storage and transport,and oil refinery industries were the five largest emitters, accounting for55% of the total emissions.

A province-level VOCs emissions inventory for industries in China in2018 was also developed. As shown in Fig. 3, Guangdong, Shandong,Zhejiang, and Jiangsu were the four largest contributors to VOCs

0

400

800

1200

1600

Gu

ang

do

ng

Shan

don

g

Zhej

iang

Jian

gsu

Fuji

an

Hen

an

Nia

onin

g

Shaa

nx

i

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ei

Sic

hu

an

Shan

ghai

Hu

bei

Tia

nji

n

An

hu

i

Hei

long

jian

g

Xin

jian

g

Em

issi

ons

(kt)

Production of VOCs

Processes using VOCs as raw materials

VOCs emission intensity

Fig. 3. Industrial VOCs emissions inventor

emissions, with industrial VOCs emissions greater than 1000 kt, and to-gether accounted for 41% of total emissions. These provinces all havehigh levels of economic development and industrial production. By con-trast, Guizhou, Hainan, Qinghai, and Tibet had VOCs emissions below100 kt, corresponding to less than 2% of total industrial sources. Detaileddata for each province are summarized in Table S3 in the SupplementalMaterials. In terms of the intensity of VOCs emissions in each province(i.e., VOCs emissions per unit of industrial GDP contribution), Hainan,Ningxia, Tibet, Heilongjiang, and Xinjiang had the highest intensity ofVOCs emissions, with more than 80 t VOCs·100 million−1 yuan. Thesehigh values are most likely related to the numerous traditional

0

20

40

60

80

100

120

Shan

xi

Inn

er M

on

go

lia

Jili

n

Hu

nan

Gu

ang

xi

Jian

gx

i

Ch

on

gq

ing

Bei

jing

Yunn

an

Gan

su

Nin

gx

ia

Gu

izho

u

Hai

nan

Qin

gh

ai

Tib

et

Em

issi

ons

inte

nsi

ty

(t V

OC

s ·

10

0 m

illi

on

- 1)

Storage and transport

Processes using VOCs-containing products

y for each province of China in 2018.

6 X. Liang et al. / Science of the Total Environment 745 (2020) 140838

industries in these provinces that have high VOCs emissions and littleeconomic benefit. By contrast, Chongqing, Hubei, Jiangxi, Guizhou, andInner Mongolia had the lowest intensity of VOCs emissions, with lessthan 30 t VOCs·100 million−1 yuan.

Fig. 3 shows province-level VOCs emissions by source category. Theprocesses using VOCs-containing products category was the greatestcontributor to emissions in most provinces, including Guangdong,Shandong, Zhejiang, and Jiangsu. Nevertheless, storage and transportand production of VOCs were the largest contributors in Heilongjiang,Xinjiang, Hainan, and Ningxia. The industries that contributed to VOCsemissions in each provincewere closely related to their industrial struc-ture. For example, 35% of China's crude oil processing by volume occursin Shandong and Liaoning. The contribution to VOCs emissions of the oilrefinery industry in these two provinces was large, representing thethird (10%) and second (18%) greatest emissions source, respectively.For the basic organic chemical industry, 37% of VOCs emissions origi-nated from methanol manufacturing. The province with the largestmethanol production is Inner Mongolia, which produces 20% ofChina's methanol. The basic organic chemical industry was the largestemitter in Inner Mongolia, accounting for 24% of total emissions. Cokeproduction in Shanxi (20%) was the highest in China and representedthe largest emissions source in that province, contributing 45% of totalVOCs emissions. In general, the top three VOCs emissions sources ineach provincewere concentrated among fourmajor sources: the indus-trial coating, printing, basic organic chemical industries and gasolinestorage and transport.

As shown in Fig. 4, annual industrial VOCs emissions in China in-creased from 8777 kt in 2011 to 12,446 kt in 2018, with an average an-nual growth rate of 5.2%. According to historical trends in industrialVOCs, this period can be divided into two stages. From 2011 to 2014,total emissions increased at a high average annual growth rate of 9.2%,and the four main source categories listed above had their average an-nual growth rate of 5.8%, 6.6%, 9.9% and 10.4%, respectively. Thesesharp increases were mainly due to rapid economic development.From 2015 to 2018, total emissions had a low growth rate of 2.2% andemissions of the four source categories grew slowly, in particular pro-cesses using VOCs-containing products, with a negative growth rate of2.9%. During this period, growth in average annual emissions for the cat-egories production of VOCs and processes using VOCs-containing prod-ucts decreased sharply to 1.9% and 3.0%, respectively. For “storage andtransport”, the growth rate was slightly reduced, from 6.6% in2011–2014 to 5.3% in 2015–2018. For storage and transport, the growth

0

4000

8000

12000

16000

2011 2012 2013 201

Em

issi

ons

(kt)

Production of VOCs

Processes using VOCs as raw materials

Fig. 4. Temporal trends in industrial VO

rate decreased slightly, from 6.6% in 2011–2014 to 5.3% in 2015–2018.In general, the slow growth in the emissions was mainly due to indus-trial structural upgrades and the implementation of VOCs source con-trols in China, such as those described in the Volatile OrganicCompound Reduction Action Plan for Key Industries, “Thirteenth Five-yearPlan” Volatile Organic Compound Pollution Prevention Work Plan, and“Thirteenth Five-year Plan” Comprehensive Work Plan for Energy Savingand Emissions Reduction (MEE, 2016, 2017; MIIT, 2017).

3.3. Uncertainties of industrial VOCs emissions inventory

Table 2 compares the industrial VOCs emissions estimates in thisstudy to those in other studies. To make clear comparisons, we inte-grated previous estimates into the four categories based on our sourceclassification (i.e., production of VOCs, storage and transport, industrialprocesses using VOCs as raw materials, and processes using VOCs-containing products). The most recent national VOCs emissions inven-tories are focused around the period 2011–2013, including the2011–2013 industrial VOCs emissions inventory compiled by Zhenget al. (2017) and the 2008–2013 anthropogenic VOCs emissions inven-tory reported by Wu et al. (2016) and Wu and Xie (2017).

Our results for total industrial VOCs emissions in Chinawere smallerthan those reported previously. Those studies generally covered morenon-industrial sources than this study. For example, among processesusing VOCs-containing products, Wu et al. (2016) and Wu and Xie,2017 established inventories for non-industrial sources such as pesti-cide utilization, asphalt pavement, building painting, cooking, drycleaning, and personal care products. Within the same category, the in-ventory established by Zheng et al. (2017) included non-industrialsources such as architectural decorations and dry cleaning. We updatedemissions factors for important industrial sources, including the oil re-finery, synthetic leather, printing, industrial coating, and electronicsmanufacturing industries. Overall, these emissions factors were smallerthan those of Zheng et al. (2017) and Wu et al. (2016), Wu and Xie(2017). Compared to those established by Zheng et al. (2017) and Wuet al. (2016), which were mainly based on the results of earlier studiesin China and in developed countries, our emissions factors aremore rep-resentative of current VOCs emissions in China.

Monte Carlo simulation was used to quantitatively assess uncer-tainty in the industrial VOCs emissions inventory for China in 2018.The activity data and emissions factorswere assumed to follow anormaldistribution. Thus, themean and standard deviation of each sourcewere

4 2015 2016 2017 2018

Storage and transport

Processes using VOCs-containing products

Cs emissions from 2011 to 2018.

Table 2Comparison of industrial VOCs emissions inventories for China (units: Tg).

Reference Year Production of VOCs Storage and transport Processes using VOCs as raw materials Processes using VOCs-containing products Total

This study 2013 1.29 1.26 2.12 5.92 10.59Zheng et al., 2017 2013 3.03 1.51 2.67 22.15 29.36Wu and Xie, 2017 2013 2.90 0.75 5.48 8.33 17.46This study 2012 1.23 1.2 1.97 5.22 9.62Zheng et al., 2017 2012 21.0Wu et al., 2016 2012 3.01 0.7 5.42 8.57 17.7This study 2011 1.16 1.12 1.77 4.72 8.77Zheng et al., 2017 2011 15.3

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determined. We assumed that the basic characteristic of each sourcewas the mean, and we estimated the standard deviation from the coef-ficient of variation (CV). The CVs of activity data and emissions factorswere mainly obtained from the TRACE-P inventory and the research ofQiu et al. (2014) and Wei et al. (2011). The uncertainty in activity dataand emissions factors is summarized by source in Table S4 in the Sup-plemental Materials. The results of Monte Carlo simulation are shownin Table 3. The uncertainty in total industrial emissions in 2018 was[−33%, +47%] at the 95% confidence level. For the four source catego-ries—production of VOCs, storage and transport, industrial processesusing VOCs as raw materials, and processes using VOCs-containingproducts—uncertainty was [−53%, +70%], [−76%, +131%], [−45%,+62%], and [−48%, +76%], respectively.

3.4. Species- and source–based emissions inventories

A speciated VOCs emissions inventory was developed for industrialsources in China in 2018. As shown in Fig. 5, the highest emissions,representing 40% of industrial VOCs, was for aromatics. Industrial emis-sions of alkanes, OVOCs, alkenes/alkynes, and halocarbons were 28%,18%, 6.9%, and 4.2% of the total, respectively. Alkanes were the major

Table 3Uncertainties of sector-based industrial VOCs emissions in China.

Emissions sources

① Production of VOCs Crude oil & natural gas exOil refinery industryBasic organic chemical inFertilizer industry

② Storage and transport Crude oilGasolineDiesel

③ Processes using VOCs as raw materials Paints and similar producAdhesive industrySynthetic fiber industrySynthetic resin industrySynthetic rubber industryRubber products industryFood and drink processinDaily chemical industryPharmaceutical industry

④ Processes using VOCs-containing products Coke industryTextile printing industrySynthetic leather industryPulp and paper industryPrintingWood processing industrShoemaking industryIndustrial coating industrElectronic manufacturingMetal smelting industryNon-metallic mineral proWaste disposalThermal powerHeatingIndustrial consumption

species in the categories of production of VOCs (50%) and storage andtransport (76%). The main contributor to industrial processes usingVOCs as raw materials emissions was OVOCs, accounting for 42% ofthe total, whereas aromatics had emissions of 53% for processes usingVOCs-containing products.

The top four species contributing to aromatics emissions were tolu-ene at 11%, ethyl benzene at 8.1%, m/p-xylene at 7.5%, and styrene at2.6%. Isopentane, n-propane, and n-butane, accounted for 6.4%, 3.2%,and 2.8% of total industrial emissions, respectively, and were the maincontributing species among alkanes. Ethyl acetate, isopropyl alcohol,and acetone were the OVOCs species with the greatest contributions,making up 5.3%, 3.3%, and 3.2% of total industrial emissions, respec-tively. Together these species were the top 10 contributors to emissionsand made up 53% of total industrial emissions. Detailed data on thespeciated VOCs emissions inventory for industrial sources are listed inTable S5 in the Supplemental Materials.

The top threemajor sources for the top 10 species are summarized inTable 4. Overall, the top three major sources contributed 67%–98% toemissions of each species. The industrial coating sector was the largestcontributor to toluene, ethyl benzene, and m/p-xylene emissions, ac-counting for 57%, 79%, and 74% of the total, respectively. In particular,

95% confidence interval

ploitation [−72%, +95%] [−53%, +70%][−91%, +134%]

dustry [−66%, +100%][−84%, +139%][−92%, +219%] [−76%, +131%][−95%, +250%][−95%, +255%]

ts industry [−86%, +201%] [−45%, +62%][−99%, +282%][−75%, +140%][−70%, +116%][−96%, +206%][−96%, +189%]

g industry [−79%, +157%][−97%, +200%][−97%, +211%][−96%, +191%] [−48%,+76%][−99%, +294%][−98%, +211%][−92%, +209%][−75%, +157%]

y [−98%, +234%][−98%, +237%]

y [−79%, +153%]industry [−75%, +114%]

[−89%, +225%]ducts industry [−96%, +209%]

[−80%, +153%][−96%, +194%][−96%, +188%][−89%, +171%]

0% 20% 40% 60% 80% 100%

Using VOCs-containing products

Using VOCs as raw materials

Storage and transport

Production of VOCs

TotalAlkanes

Alkenes/Alkynes

Aromatics

Halocarbons

OVOCs

Others

Fig. 5. Speciation of industrial VOCs emissions in China in 2018.

8 X. Liang et al. / Science of the Total Environment 745 (2020) 140838

industrial protective coating production contributed greatly to thesethree aromatics. The top three species of alkanes (i.e., isopentane, n-propane, and n-butane) were emitted mainly by the storage and trans-port of crude oil and gasoline, and oil refinery industries.More than 80%of isopropyl alcohol was related to wine manufacturing in the food anddrink processing industry. As a widely used rawmaterial and thinner inprinting inks and adhesives, 50% of ethyl acetate was generated by theprinting industry. The pharmaceutical industry was the largest emitterof acetone, followed by the coke and shoemaking industries.

3.5. Species - and source-based OFP

Species- and source-based OFP values were estimated forindustrial sources in China in 2018. The estimated total industrialOFP in China in 2018 was 38,775 kt. Aromatics and alkenes/alkynescontributed 64% and 19% of total OFP, exceeding their emissionscontributions of 40% and 6.9%, respectively. By contrast, alkanes,

Table 4Source characteristics for top 10 species in terms of VOCs emissions.

Species Top three major sources

Toluene 69.27% Industrial coating industry (57.13%)Synthetic fiber industry (6.62%)Basic organic chemical industry (5.52%)

Ethyl benzene 87.31% Industrial coating industry (79.10%)Electronic manufacturing industry (4.15%)Paints and similar products industry (4.06%)

m/p-Xylene 84.53% Industrial coating industry (73.56%)Crude oil storage and transport (5.97%)Electronic manufacturing industry (5.00%)

Isopentane 86.19% Gasoline storage and transport (59.46%)Printing (18.33%)Diesel storage and transport (8.40%)

Ethyl acetate 81.74% Printing (50.03%)Synthetic leather industry (21.25%)Industrial coating industry (10.46%)

Isopropyl alcohol 97.50% Food and drink processing industry (83.77%)Printing (9.50%)Paints and similar products industry (4.23%)

Acetone 83.38% Pharmaceutical industry (54.70%)Coke industry (15.35%)Shoe making industry (13.33%)

n-Propane 71.26% Oil refinery industry (31.43%)Crude oil storage and transport (26.79%)Crude oil & natural gas exploitation (13.04%)

n-Butane 67.43% Crude oil storage and transport (37.40%)Gasoline storage and transport (16.47%)Oil refinery industry (13.56%)

Styrene 75.50% Basic organic chemical industry (34.25%)Industrial coating industry (22.59%)Synthetic fiber industry (18.66%)

halocarbons, and oxygenated organics accounted for only 10%,0.2%, and 6.5% of total OFP, respectively, compared to 28%, 4.2%,and 18% of total emissions. The OFP for individual VOCs species islisted in Table S6 of the Supplemental Materials.

Fig. 6 shows the top 20 species in termsof OFP and emissions sourcesin China in 2018. The top 20 species accounted for 85% of total OFP andonly 59% of emissions. M/p-xylene (19%), toluene (14%), ethyl benzene(7.9%) propene (6.0%), and o-xylene (5.8%) were the five most abun-dant species. Because of their MIR value, some species with a largeOFPmay not havemade a large contribution to emissions. For example,propene was the fourth largest species in terms of OFP (6.0%), but itscontribution to emissions was only 1.6%. Most of these species wereproduced mainly through processes using VOCs-containing products,includingm/p-xylene, toluene, and ethyl benzene. Some alkane species,such as isopentane and n-butane, were emitted primarily from storageand transport. Methyl cyclohexane was generated mainly from pro-cesses using VOCs-containing products. In addition, production ofVOCs was the dominant source of 1,3-butadiene and 1-pentene.

Fig. 7 compares the top 10 species based on OFP to the industrial in-ventory from our previous work (Liang et al., 2017a, 2017b) and the an-thropogenic inventory developed byWu andXie (2017). Six key speciesappear in all three top 10 lists, accounting for 54% (this study), 48%(Liang et al., 2017a, 2017b), and 43% (Wu and Xie, 2017) of total OFP.These six species are m/p-xylene, toluene, propene, ethane, o-xylene,and 1,2,4-trimethyl benzene. Despite changes to the emissions struc-ture and chemical composition of industrial sources over the past8 years, the top 10 species based on OFP did not differ greatly fromour 2010 OFP inventory (Liang et al., 2017a, 2017b), with only 1,3-buta-diene replaced by isopentane in this study. Moreover, 60% of isopentaneemissions in this study originated from gasoline storage and transport,for which the source profile (previously based on test results from be-fore 2008) was updated in this study. The 2013 anthropogenic inven-tory (Wu and Xie, 2017) included four species in the top 10 that werenot in ours: formaldehyde, acetaldehyde, styrene, and 1,3-butadiene.The source distributions of formaldehyde and acetaldehyde reportedinWu and Xie (2017) were almost entirely derived from transportationand biomass burning, which were not considered in this study. For 1,3-butadiene, nearly 30% of emissions in Wu and Xie (2017) were fromtransportation and biomass burning, which would have increased thecontribution of this species. The difference in styrene between the twotop 10 lists is mainly related to the chemical composition of sources in-cluded in each inventory, as styrene originated mainly from industrialsources in Wu and Xie (2017).

Table 5 shows the industrial source distribution of OFPEI, VOCs emis-sions, and OFP in China in 2018. Like the chemical profiles of emittedVOCs, OFPEI for a given category can be used as an indicator of potentialcontribution to O3 formation of per unit of emissions in that category.Thus, for the same emissions level, the emissions sources that should

0

2000

4000

6000

8000

0

400

800

1200

1600

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

OF

Ps

(kt)

Em

issi

ons

(kt)

Production of VOCs Storage and transport

Processes using VOCs as raw materials Processes using VOC-containing products

OFP

1: m/p-xylene 2: toluene 3: ethyl benzene 4: propene

5: o-xylenee 6: ethene 7: 1,2,4-trimethylbenzene

8: m-ethyl toluene 9: isopentane 10: 1-butene

11: 1,2,3-trimethylbenzene 12: 1,3-butadiene

13: 1,3,5-trimetylbenzene 14: styrene

15: methyl cyclohexane 16: ethyl acetate 17: n-butane

18: methyl isobutyl ketone 19: formaldehyde 20: 1-pentene

Fig. 6. Emissions and OFPs of the 20 species with the largest OFPs in China in 2018.

9X. Liang et al. / Science of the Total Environment 745 (2020) 140838

be prioritized for O3 abatement can be selected based on OFPEI. The fivelargest sources in terms of OFPEI were all in the processes using VOCs-containing products category, as their emissionswere dominated by ar-omatics (50% in this source category) with highly active chemistry.These sources included textile printing, automobile manufacturingand repair, fuel oil combustion, enameled wire industry, and industrialprotective coating. OFP depended on two key parameters of emissionsand OFPEI. Compared to emissions, the source category of processesusing VOCs-containing products with relatively high OFPEI was alsothe largest contributor to OFP, accounting for 68% of total industrialOFP. However, the OFP contribution of industrial processes using VOCsas raw materials fell to 9.5%, which was only about half of its emissionscontribution. Specifically, industrial coating with high OFPEI range of

0

10

20

)%(

sn

oitu

birtn

ocP

FO

Top 10 spe

Fig. 7. Comparison of top ten OFP-

3.3–6.6, made up 28% in terms of emissions, while its contribution toOFP was higher (43%). By contrast, Food and drink processing industrywith low OFPEI range of 0.6–1.9, accounted for 4.0% in emissions, but1.2% in OFP. Industrial coating, printing, basic organic chemical, oil refin-ery, crude oil, gasoline and diesel storage and transport, paints and sim-ilar products industry, thermal power, and waste disposal were the 10largest subsectors based on OFP, together contributing 81% of total OFP.

4. Summary and conclusions

An improved industrial VOCs emissions inventory for China duringthe period 2011–2018 and local source profiles for six specific industrieswere developed to better estimate OFP. Key VOCs species and source

cies

This study

Liang et al, 2017

Wu et al, 2017

based VOCs species in China.

Table 5OFPEI, VOCs emissions and OFP of industrial subsectors.

Emissions sources OFPEI Emissions OFP

t/t kt/y % kt/y %

① Production of VOCs 1486.95 11.95 4787.21 12.35Crude oil & natural gas exploitation Crude oil exploitation 0.60 113.46 0.91 67.58 0.17

Natural gas exploitation 0.58 57.49 0.46 33.07 0.09Oil refinery industry N.A. 3.18 603.57 4.85 1920.14 4.95Basic organic chemical industry N.A. 3.88 712.05 5.72 2765.57 7.13Fertilizer industry N.A. 2.34 0.37 0.00 0.86 0.00

② Storage and transport 1660.13 13.34 4033.73 10.40Crude oil N.A. 2.11 509.92 4.10 1074.76 2.77Gasoline N.A. 1.66 686.45 5.52 1138.82 2.94Diesel N.A. 3.92 463.75 3.73 1820.15 4.69

③ Processes using VOCs as raw materials 2073.09 16.66 3677.65 9.48Paints and similar products industry Paints and pigments industry 2.68 347.93 2.80 932.65 2.41

Ink industry 1.01 46.08 0.37 46.34 0.12Adhesive industry N.A. 2.68 67.06 0.54 179.77 0.46Synthetic fiber industry Other 2.85 266.37 2.14 759.07 1.96

Acetate fiber 1.20 54.01 0.43 64.79 0.17Synthetic resin industry N.A. 1.83 205.01 1.65 375.31 0.97Synthetic rubber industry N.A. 1.19 42.48 0.34 50.63 0.13Rubber products industry N.A. 1.70 228.59 1.84 388.30 1.00Food and drink processing industry Sugar 0.83 3.05 0.02 2.53 0.01

Vegetable oil 1.90 124.12 1.00 235.78 0.61Beer 1.84 16.39 0.13 30.16 0.08Other wine 0.60 349.57 2.81 209.63 0.54

Daily chemical industry N.A. 0.03 0.23 0.00 0.01 0.00Pharmaceutical industry N.A. 1.25 322.18 2.59 402.68 1.04

④ Processes using VOCs-containing products 7225.66 58.06 26,276.70 67.77Coke industry N.A. 1.48 547.75 4.40 809.05 2.09Textile printing industry N.A. 6.63 81.40 0.65 539.46 1.39Synthetic leather industry N.A. 1.41 313.12 2.52 440.84 1.14Pulp and paper industry Paper pulp industry 1.10 3.00 0.02 3.32 0.01

Paper products industry 2.45 5.58 0.04 13.66 0.04Printing Offset printing 2.00 135.26 1.09 270.60 0.70

Gravure printing 1.61 143.91 1.16 231.40 0.60Other printing 2.83 120.69 0.97 342.14 0.88Flexible packaging bonding 2.11 985.06 7.91 2076.33 5.35

Wood processing industry N.A. 2.99 102.96 0.83 308.18 0.79Shoemaking industry N.A. 1.44 340.12 2.73 490.01 1.26Industrial coating industry Wood products industry 3.34 704.00 5.66 2352.36 6.07

Automobile manufacturing and repair 6.55 324.65 2.61 2127.73 5.49Shipbuilding industry 4.39 201.04 1.62 881.86 2.27Industrial protective coating 5.13 2221.93 17.85 11,397.24 29.39

Electronic manufacturing industry Copper clad laminate industry 3.21 65.45 0.53 209.91 0.54Enameled wire industry 5.63 78.72 0.63 443.23 1.14Other 2.83 69.63 0.56 196.76 0.51

Metal smelting industry Hot rolling 1.09 1.36 0.01 1.49 0.00Other metals smelting 4.01 28.35 0.23 113.63 0.29

Non-metallic mineral products industry Cement industry 1.29 26.49 0.21 34.07 0.09Waste disposal Landfill & compose 1.86 31.92 0.26 59.21 0.15

Incineration 4.49 152.77 1.23 685.61 1.77Wastewater treatment 5.12 54.74 0.44 280.25 0.72

Thermal power Coal 4.07 289.09 2.32 1175.38 3.03Fuel 6.10 0.02 0.00 0.11 0.00

Heating Coal 4.07 59.11 0.47 240.33 0.62Fuel 6.10 0.12 0.00 0.72 0.00

Industrial consumption Coal 4.07 121.64 0.98 494.59 1.28Fuel 6.10 0.46 0.00 2.84 0.01LPG 2.81 0.02 0.00 0.05 0.00Natural gas 3.55 15.30 0.12 54.31 0.14

10 X. Liang et al. / Science of the Total Environment 745 (2020) 140838

characteristics in terms of emissions and OFPwere investigated and an-alyzed, which would be helpful for governments to make efficientreactivity-based O3 control strategies in China.

Annual industrial VOCs emissions in China increased from 8777 kt in2011 to 12,446 kt in 2018, with an average annual growth rate of 5.2%.The average annual growth rate for emissions during 2015–2018 waslower than 2011–2014, which could be related to China's industrialstructural upgrade and implementation of VOCs source control duringthe 13th Five-Year Planperiod. Industrial coating, printing, basic organicchemical, gasoline storage and transport, and oil refinery industrieswere the five largest emitters, accounting for 55% of the total emissions.

Guangdong, Shandong, Zhejiang and Jiangsu were the four largest con-tributors to emissions, contributing 41% of total emissions. Toluene,ethyl benzene, m/p-xylene, isopentane, ethyl acetate, isopropyl alcohol,acetone, n-propane, n-butane, and styrene were the top 10 species interms of emissions. Considering the different photochemical reactivityof various VOCs species, m/p-xylene, toluene, ethyl benzene, propene,o-xylene, ethene, 1,2,4-trimethylbenzene, m-ethyl toluene, isopentane,and 1-butene were identified as the top 10 species in terms of OFP. Thetop 20 species in terms of OFP accounted for 85% of total OFPs and only59% of emissions. The industrial coating, printing, basic organic chemi-cal, oil refinery, crude oil, gasoline and diesel storage and transport,

11X. Liang et al. / Science of the Total Environment 745 (2020) 140838

paints and similar products industry, thermal power andwaste disposalwere the 10 largest OFP-based sources, contributing 81% of total OFP.

Given the severity of O3 pollution in China, more effective controlmeasures are urgently needed. A reactivity-based VOCs control strategymay be advisable. According to the OFP-based emissions inventory inthis study, priority should be given to the top 20 or more species withhigh reactivity and the 10 industrial sources with the largest contribu-tions to OFP to promote further O3 reduction in the future.

CRediT authorship contribution statement

Xiaoming Liang: Conceptualization, Writing - original draft,Methodology. Xibo Sun: Investigation, Formal analysis, Visualiza-tion. Jiantie Xu: Writing - review & editing. Daiqi Ye: Supervision,Writing - review & editing.

Declaration of competing interest

The authors declare that they have no known competing financialinterests or personal relationships that could have appeared to influ-ence the work reported in this paper.

Acknowledgments

This work was supported by a grant from the National Environmen-tal Protection Project: The Second National Survey of Pollution Sources(No numbers).

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.scitotenv.2020.140838.

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