Pollution Characteristics and Health Risk Assessment of Summertime Atmospheric Volatile Halogenated Hydrocarbons in a Typical Urban Area of Beijing, China

atmosphere

Article Pollution Characteristics and Health Risk Assessment of Summertime Atmospheric Volatile Halogenated Hydrocarbons in a Typical Urban Area of Beijing, China

1,2, 1,3, 1, 1 4 1,5 Yuanyuan Ji †, Linghong Xu †, Hong Li *, Chuhan Wang , Dongyao Xu , Lei Li , Hao Zhang 1, Jingchun Duan 1, Yujie Zhang 1, Xuezhong Wang 1, Weiqi Zhang 1 , Fang Bi 1, Yizhen Chen 1, Yanting Yu 6 and Lingshuo Meng 1

1 State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China; [email protected] (Y.J.); [email protected] (L.X.); [email protected] (C.W.); [email protected] (L.L.); [email protected] (H.Z.); [email protected] (J.D.); [email protected] (Y.Z.); [email protected] (X.W.); [email protected] (W.Z.); [email protected] (F.B.); [email protected] (Y.C.); [email protected] (L.M.) 2 College of Earth Sciences, Jilin University, Changchun 130061, China 3 Daishan Environmental Protection Bureau, Zhoushan 316200, China 4 School of Chemical & Environmental Engineering, China University of Mining and Technology, Beijing 100083, China; [email protected] 5 Academy of Environmental Planning and Design, Co., Ltd., Nanjing University, Nanjing 210093, China 6 Puyang Research Institute of Environmental Sciences, Puyang 457000, China; [email protected] * Correspondence: [email protected] These authors contributed equally to this work. † Received: 16 August 2020; Accepted: 16 September 2020; Published: 23 September 2020

Abstract: Twenty-three atmospheric volatile halogenated hydrocarbons (VHHs) were detected in a typical urban area of Beijing, China from 24 August to 4 September, 2012. The mean and range in daily mass concentrations of the 23 VHHs were 30.53 and 13.45–76.33 µg/m3, respectively. Seven of those VHHs were controlled ozone-depleting substances in China, with a mean of 12.95 µg/m3, accounting for 42.43% of the total. Compared with other national and international cities, the concentrations of the selected 11 VHHs in this study were relatively higher. Dichloroethane had the highest mass concentration, followed by diﬂuorochloromethane. Maxima of total VHHs occurred within the period 8:30–9:00 a.m., while minima occurred during 1:30–2:00 p.m. Source apportionment suggested that the main sources of VHHs in the study area were solvents usage and industrial processes, leakage of chloroﬂuorocarbons banks, refrigerants, and fumigant usage. Among the selected 7 VHHs, trichloromethane, tetrachloromethane, 1,2-dichloroethane, and 1,4-dichlorobenzene posed potential carcinogenic risks to exposed populations, while none of the selected 11 VHHs posed appreciable non-carcinogenic risks to exposed populations. The carcinogenic risks from atmospheric VHHs in Beijing are higher than in other Chinese cities, indicating that it is necessary to implement immediate control measures for atmospheric VHHs in Beijing.

Keywords: ambient air; volatile halogenated hydrocarbons; pollution status; sources; health risk assessment; Beijing

Atmosphere 2020, 11, 1021; doi:10.3390/atmos11101021 www.mdpi.com/journal/atmosphere Atmosphere 2020, 11, 1021 2 of 19

1. Introduction Volatile halogenated hydrocarbons (VHHs) in the atmosphere include ozone-depleting substances (ODS) such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) as well as toxic and harmful VHHs (THVHHs; e.g., chlorobenzene, chloroform, and chloroethylene). ODS could deplete the stratospheric ozone layer, enhancing the greenhouse effect [1], while THVHHs are generally irritating and corrosive, causing damage to human skin, liver, heart, kidney, pancreas, and the central nervous system [2–4]. Some THVHHs are recognized as carcinogenic, teratogenic, and mutagenic compounds [4–6]. Compared with other atmospheric pollutants, little research has been carried out on the characterization or the health risk assessment of VHHs in China [7–19]. Previous studies have shown that in some Chinese cities, especially Hong Kong and Guangzhou, the concentrations of VHHs in ambient air are higher than those in other international cities [9,11]. In particular, some species of VHHs identified in urban monitoring sites in Chinese cities pose a carcinogenic risk to exposed populations [12]. Given that the environmental management strategy in China is transitioning from “Passive Response” to “Active Prevention and Control”, control measures for VHHs should now be emphasized to improve air quality. Beijing, the center of politics, culture, and economics, is featured with a dense population, huge vehicle amounts, many industry factories, and complicated air pollutants emissions. Recently, increasing occurrences of the haze with a wide area range and long duration in Beijing have attracted great attention from the central government, municipal government, and general public. In order to formulate accurate prevention and control measures for protecting the stratospheric ozone layer and human health, it is necessary to study the characteristics and health risks of VHHs. In this paper, ambient VHHs samples were collected in an urban area of Beijing from 24 August to 4 September 2012. Ambient concentrations, temporal variations, and sources of VHHs were analyzed and health risks of selected THVHHs were assessed. These data support further recognition of the health risks of VHHs and implementation of effective control measures for VHH pollution in Beijing in the near future.

2. Materials and Methods

2.1. Sample Collecting Air samples were collected on the roof of the Supersite for Urban Air Comprehensive Observation and Research at the Chinese Research Academy of Environmental Sciences in the northeastern urban area of Beijing (40◦020 N, 116◦250 E) (Figure1). This site is located 15 m above the ground, about 2 km north of the North Fifth Ring Road, 3.6 km from the Olympic park, 200 m east of Subway Line 5 and Beiyuan Road, and 100 m north of Chunhua Road. The site is in a residential and commercial area, and there are no obvious local air pollution sources nearby. The population density surrounding the sampling site is 8038 people per square kilometer [20]. Thus, our air pollution monitoring results can reﬂect the ambient air quality of the resident urban population in this area. Therefore, these monitoring data can be used to investigate pollution levels and to determine health risks of VHHs in the ambient air for this typical urban area of Beijing. Atmosphere 2020, 11, 1021 3 of 19 Atmosphere 2020, 11, x FOR PEER REVIEW 3 of 19

Figure 1. Location of sampling site and surroundings [[21].21].

Samples were were collected collected from from 24 Au 24gust August to 4 September to 4 September 2012 over 2012 four over 30-min four periods: 30-min 8:30–9:00 periods: 8:30–9:00a.m., 1:30–2:00 a.m., 1:30–2:00p.m., 6:00–6:30 p.m., 6:00–6:30 p.m., and p.m., 10:00–10:30 and 10:00–10:30 p.m. However, p.m. However, sampling sampling was postponed was postponed from fromnoon noonon 1 onSeptember 1 September to the to themorning morning of 2 of September 2 September because because of of rain. rain. In In total, total, 43 43 air air samples samples were collected in SUMMA canisters (Entech Instruments, Inc., Simi Valley, CA,CA, USA);USA); thirtythirty canisterscanisters had volumes ofof 3.23.2 L,L, whilewhile thethe others others had had volumes volumes of of 3.0 3.0 L. L. The The recommended recommended TO-15 TO-15 sampling sampling method method of theof the US US Environmental Environmental Protection Protection Agency Agency (US (US EPA) EPA) was was used used as ouras our sampling sampling method method [22 ].[22]. Before sampling, all canisters were cleaned using a canister cleaner (3100A, Entech Instruments, Inc., SimiSimi Valley,Valley, CA,CA, USA) California, and vacuumed USA) and to vacuumed 50 mtorr. to The 50 sampling mtorr. The speed sampling was controlled speed was by acontrolled ﬂow-limiting by a valve. flow-limiting The canisters valve. were The placed canisters 1.5 mwere above placed the rooftop. 1.5 m Meteorologicalabove the rooftop. data atMeteorological the sampling data site, at including the sampling wind site, direction, including wind wind speed, direction, temperature, wind speed, dew point temperature, temperature, dew solarpoint radiation,temperature, ultraviolet solar radiation, radiation, ultraviolet and visibility, radiation, were monitored and visibility, hourly were using monitored an automatic hourly weather using stationan automatic (Vaisala weather Inc., Helsinki, station (Vaisala Finland) Inc., from Helsinki, 28 August Finland) to 4 September from 28 August 2012. to 4 September, 2012.

2.2. Sample Analysis All air samplessamples werewere analyzedanalyzed usingusing cryogeniccryogenic coldcold traptrap preconcentrationpreconcentration followed by gas chromatography (GC) coupled with mass spectrometryspectrometry (MS) and flameflame ionization detection (FID) withinwithin 1515 days.days. Each volatile organic compound (VOC) sample was enriched and concentrated by passing it through the Entech 7100A pre-concentratio pre-concentrationn system system (Entech (Entech Instruments, Instruments, Inc., Inc., Simi Simi Valley, Valley, CA, USA), whereby waterwater andand COCO22 were also removed from the sample. VOCs were rapidly gasifiedgasified and fed intointo thethe GC-MSGC-MS/FID/FID systemsystem (GC,(GC, HP-7890A, HP-7890A, Agilent Agilent Technology, Technology, Inc., Inc., Santa California, Clara, California,USA; MS, USA;HP-5975C, MS, HP-5975C,Agilent Technology, Agilent Technology, Inc., California, Inc., SantaUSA) Clara,to be separated California, and USA) quantitatively to be separated analyzed and quantitatively[23]. Ninety-seven analyzed VOCs, [23 ].including Ninety-seven 25 VHHs, VOCs, were including separated 25 VHHs, by the were DB-624 separated chromatographic by the DB-624 chromatographic column (60 m 0.25 mm 1.8 µm; J&W Scientific, Folsom, CA, USA) and the PLOT column (60 m × 0.25 mm × 1.8 µm;× J&W Scientific,× Folsom, CA, USA) and the PLOT chromatographic chromatographic column (30 m 0.25 mm 3.0 µm; J&W Scientific, Folsom, CA, USA). All these column (30 m × 0.25 mm × 3.0× µm; J&W ×Scientific, Folsom, CA, USA). All these species were speciesquantitatively were quantitatively analyzed by analyzed MS or FID. by MSFor orthe FID. MS For analysis, the MS the analysis, temperature the temperature and energy and of energy the ion of thesource ion were source 200 were °C and 200 ◦70C andeV, respectively; 70 eV, respectively; the scanning the scanning speed was speed 4 scan/s; was 4 scan and/ s;the and scanning the scanning scope scopewas 35–350 was 35–350 amu. amu.For the For chromatographic the chromatographic analysis, analysis, the thetotal total run run time time was was 47 47 min. min. The The initial temperature inin thethe GCGC ovenoven waswas keptkept atat 3030 ◦°CC for 7 min, then increased to 120 ◦°CC at a rate of of 5 5 °C/min.◦C/min. It waswas keptkept atat 120120◦ °CCfor for 5 5 min, min, and and then then increased increased to to 180 180◦C °C with with a ratea rate of of 6 ◦ 6C /°C/min,min, and and held held at 180at 180◦C for°C for 7 min. 7 min. Standard compoundscompounds and and internal internal standards standards were were used used to to build build multi-point multi-point calibration calibration curves curves for quantitativefor quantitative analysis analysis of the ofVOCs. the VOCs. The standardThe standa gasesrd gases were multi-componentwere multi-component gas, including gas, including 56 VOCs 56 (PAMS,VOCs (PAMS, Scott Specialty Scott Specialty Gases Company, Gases Company, Plumsteadville, Plumsteadville, PA, USA), PA, as wellUSA), as as the well multi-component as the multi- standardcomponent gas standard recommended gas recommended in the TO-15 methodin the TO (Scott-15 method Specialty (Scott Gases Specialty Company, Gases Plumsteadville, Company, PA,Plumsteadville, USA). The three PA, USA). internal The standard three internal compounds standard were compounds bromochloromethane, were bromochloromethane, p-difluorobenzene, p- anddifluorobenzene, 1-bromo-3-fluorobenzene and 1-bromo-3-fluorobenzene (Scott Specialty Gases (Scott Company, Specialty Plumsteadville, Gases Company, PA, USA). Plumsteadville, PA, USA).

Atmosphere 2020, 11, 1021 4 of 19

Twenty-five VHHs were analyzed, including 4 chlorofluorocarbons (CFCs), 1 hydrochlorofluorocarbons (HCFCs), 10 chloroalkanes, 4 chloroalkenes, 3 chlorinated benzenes, 2 bromohydrocarbons, and 1 bromine chlorine hydrocarbon. However, 1,1,1-trichloroethane and bromine chlorine hydrocarbon were not detected in all samples. Daily average mass concentrations of the other 23 VHHs, as well as their method detection limits and linear correlation coefficients (r2) of their working curves, are given in Table1.

Table 1. Mass concentrations of 23 volatile halogenated hydrocarbons (VHHs) at the study site.

Range Mean MDL Category VHH Species 2 µg/m3 * pptV µg/m3 * pptV (pptV) r Trichlorofluoromethane ** 1.69–2.98 302.8–537.1 2.17 391.1 4.2 0.999 Dichlorodifluoromethane ** 2.96–4.83 613.3–997.2 3.46 710.8 2.6 0.999 Chlorofluorocarbons Dichlorotetrafluoroethane ** 0.12–0.18 18.0–26.0 0.15 22.4 3.3 0.999 1,1,2-Trichlorotrifluoroethane ** 0.65–0.83 86.9–107.6 0.72 95.9 4.0 0.999 Hydrochlorofluorocarbons Chlorodifluoromethane ** 1.43–27.56 407.8–7891.8 5.55 1589.3 2.8 0.999 Monochloromethane 1.36–6.10 664.2–2997.6 2.87 1413.6 3.4 0.999 Dichloromethane 1.23–15.95 352.0–4656.7 6.43 1883.7 8.4 0.999 Trichloromethane 0.11–2.67 23.0–554.4 0.81 168.3 5.2 0.999 Tetrachloromethane ** 0.62–1.30 99.6–214.2 0.84 135.6 4.1 0.999 Chloroalkanes Monochloroethane ND–0.60 ND–233.6 0.15 59.6 10.0 0.999 1,1-Dichloroethane ND–0.71 ND–178.1 0.22 55.9 9.1 0.999 1,2-Dichloroethane 0.37–10.26 91.4–2571.2 3.09 776.0 11.2 0.999 1,1,2-Trichloroethane ND–0.81 ND–151.0 0.26 48.5 8.5 0.998 1,2-Dichloropropane 0.15–9.17 32.0–2025.2 2.38 523.0 9.90 0.998 1,1-Dichloroethene ND–0.30 ND–78.1 0.01 2.4 15.3 0.999 Trichloroethene ND–0.57 ND–107.9 0.18 33.7 18.1 0.999 Chloroalkenes Tetrachloroethene ND–1.76 ND–263.5 0.43 64.6 14.4 0.998 trans-1,3-Dichloropropene ND–0.13 ND–28.8 0.01 1.7 19.9 0.997 Chlorobenzene ND–0.65 ND–142.3 0.13 29.5 19.3 1.000 Chlorinated benzenes 1,3-Dichlorobenzene ND–0.85 ND–148.2 0.03 4.6 17.9 0.998 1,4-Dichlorobenzene ND–1.92 ND–328.7 0.54 90.5 17.9 0.998 Bromomethane ** 0.03–0.10 9.0–25.8 0.06 15.4 6.2 0.999 Bromohydrocarbons Tribromomethane ND–0.34 ND–33.7 0.03 3.4 8.0 0.999 7 controlled ODS in China 7.69–36.17 1557.0–9485.0 12.95 2960.5 23 VHHs 13.45–76.33 3319.2–20702.4 30.53 7968.5 MDL: method detection limit; ND: not detected. * Real-time temperature and pressure were used for the unit conversion. ** controlled ozone-depleting substances (ODS) in China.

2.3. Quality Assurance and Quality Control Quality assurance and quality control in this study relied on method detection limits, retention times, detection accuracy, and reference sample analyses. The standard working curves were established using standard gases outlined in TO-15, PAMS, and three internal standard gases. The collection and analysis process for all samples were performed according to the requirements of the US EPA Compendium Method TO-15 [22]. The R2 of the calibration curves for all samples was >0.998 and the range in deviation between our results and theoretical values was 1 20%. ± 2.4. Data Processing Levels, temporal variations, sources, and health risk were studied based on the data in this observation. It should be noted that the related conclusions based on these limited data may have some uncertainty. In order to obtain more general research results, long-term and systematic observations of atmospheric VHHs are needed.

2.4.1. Source Apportionment Using Positive Matrix Factorization The positive matrix factorization (PMF) model is a multivariate factor analysis tool and matrix decomposition method that integrates error estimates in data to the restricted-weight, least-squares linear model. It is widely used to analyze the source of aerosols, wet and dry deposition, and VOCs [24,25]. In this study, PMF5.0 recommended by US EPA was used to analyze the sources of atmospheric VHHs in the study area. The details of species selection and data processing were Atmosphere 2020, 11, 1021 5 of 19 documented elsewhere [21,26]. In brief, species with no available mixing ratios or species for which >25% samples had mixing ratios lower than the detection limit have been removed. Species with high reactivity or low mixing ratios or those which were not important tracers of pollution also have been removed [26]. Eventually, 19 VHHs were selected to analyze the sources.

2.4.2. Health Risk Assessment Health risk assessment methods can be used to estimate the adverse eﬀect of pollutants on human health. Such methods have been adopted worldwide and are continually updated. In 1983, the US National Academy of Sciences proposed a four-step health risk assessment, which includes hazard identiﬁcation, dose–response assessment, exposure assessment, and risk characterization [27]. Given the carcinogenicity of some pollutants, the health risk assessment is divided into carcinogenic risk and non-carcinogenic risk assessments; both assessments should have been carried out for carcinogenic pollutants. The US EPA proposed a health risk assessment method based on respiratory rate and body weight for inhalable pollutants in 1989 [28], and updated it in 2009 [29]. In this latest version, concentrations of the pollutant in air is used as the exposure metric (e.g., mg/m3), rather than its inhalation intake based on human inhalation rate and body weight. This methodology has been widely accepted for human health assessment worldwide [30–34]. We used the method proposed by the US EPA to make the health risk assessment in this study. Here, carcinogenic risk is expressed as Risk (dimensionless), while non-carcinogenic risk is expressed using the hazard index (HI, dimensionless), i.e., a sum of the hazard quotients (HQ, dimensionless) for several pollutants [29]. The details are shown as below: The chronic or subchronic exposure concentration (EC, µg/m3) can be estimated with the following equation: EC = (CA ET EF ED)/AT (1) × × × The Risk can be estimated with the following equation:

Risk = IUR EC . (2) × The HQ and HI can be estimated with the following equation:

HQ = EC/(RfC 1000), (3) × Xn HI = HQi. (4) i=1 In Equations (1)–(4), CA (µg/m3) is the contaminant concentration in air; ET (24 h/d) is exposure time; EF (365 day/year) is exposure frequency; ED (70 year) is exposure duration; AT (70 year 365 day × 24 h) is averaging time; IUR (m3/µg) is inhalation unit risk [35]; and RfC (mg/m3) is the reference × concentration [35].

3. Results and Discussion

3.1. Ambient Levels and Composition Characteristics The average and range of the total mass concentration in ambient air for 23 VHHs in the study area were 30.53 and 13.45–76.33 µg/m3, respectively. Among the 23 VHHs, 7 VHHs were controlled ODS in China. The average and range of the seven VHHs were 12.95 and 7.69–36.17 µg/m3, respectively, accounting for 42.43% of the 23 VHHs. The daily average mass concentrations of CFCs, HCFCs, chloroalkanes, chloroalkenes, chlorinated benzenes, and bromohydrocarbons were 6.51, 5.55, 17.06, 0.63, 0.70, and 0.09 µg/m3, respectively, yielding percentages of 21.32%, 18.17%, 55.87%, 2.05%, 2.28%, and 0.31% of the total mass concentration of the 23 VHHs (Figure2). Chloroalkanes, CFCs, and HCFCs were the main VHHs in this study area, accounting for 95% of the 23 VHHs. The daily Atmosphere 2020, 11, x FOR PEER REVIEW 6 of 19

5.55,Atmosphere 17.06, 2020 0.63,, 11, 0.70,x FOR andPEER 0.09 REVIEW µg/m 3, respectively, yielding percentages of 21.32%, 18.17%, 55.87%,6 of 19 2.05%, 2.28%, and 0.31% of the total mass concentration of the 23 VHHs (Figure 2). Chloroalkanes, 3 CFCs,5.55, 17.06, and HCFCs 0.63, 0.70, were and the0.09 main µg/m VHHs, respectively, in this study yielding area, accounting percentages for of 95% 21.32%, of the 18.17%, 23 VHHs. 55.87%, The dailyAtmosphere2.05%, 2.28%,average2020, 11 and, 1021 0.31%mass of theconcentrations total mass concentration of dichloromethane, of the 23 VHHs (Figurechlorodifluoromethane, 2). Chloroalkanes,6 of 19 dichlorodifluoromethane,CFCs, and HCFCs were the 1,2-dichloroethane, main VHHs in this studymonochloromethane, area, accounting for1,2-dichloropropane, 95% of the 23 VHHs. andThe daily average mass concentrations of dichloromethane, chlorodifluoromethane, trichlorofluoromethaneaverage mass concentrations were 6.43, of dichloromethane, 5.55, 3.46, 3.09, 2.87, chlorodifluoromethane, 2.38, and 2.17 µg/m3, dichlorodifluoromethane, respectively, accounting dichlorodifluoromethane, 1,2-dichloroethane, monochloromethane, 1,2-dichloropropane, and for1,2-dichloroethane, 21.07%, 18.17%, 11.35%, monochloromethane, 10.13%, 9.40%, 1,2-dichloropropane, 7.79%, and 7.09% of andthe total trichlorofluoromethane mass concentration were of the 6.43, 23 trichlorofluoromethane were 6.43, 5.55, 3.46, 3.09, 2.87, 2.38, and 2.17 µg/m3, respectively, accounting VHHs5.55, 3.46, (Figure 3.09, 3). 2.87, Thus, 2.38, these and seven 2.17 µ gspecies/m3, respectively, were the main accounting VHHs in for this 21.07%, study, 18.17%, accounting 11.35%, for 10.13%,85% of for 21.07%, 18.17%, 11.35%, 10.13%, 9.40%, 7.79%, and 7.09% of the total mass concentration of the 23 the9.40%, total 7.79%, mass andconcentration 7.09% of the of totalthe 23 mass VHHs. concentration of the 23 VHHs (Figure3). Thus, these seven VHHs (Figure 3). Thus, these seven species were the main VHHs in this study, accounting for 85% of species were the main VHHs in this study, accounting for 85% of the total mass concentration of the the total mass concentration of the 23 VHHs. 23 VHHs.

Figure 2. Composition of atmospheric volatile halogenated hydrocarbons at the study site (by

category). Figure 2.2.Composition Composition of atmosphericof atmospheric volatile volatile halogenated halogenated hydrocarbons hydrocarbons at the studyat the site study (by category). site (by category).

FigureFigure 3. CompositionComposition of of atmospheric atmospheric volatile volatile halogena halogenatedted hydrocarbons hydrocarbons (VHHs) (VHHs) at at the the study study site site

with respect to dominant chemical species. Figure 3. Composition of atmospheric volatile halogenated hydrocarbons (VHHs) at the study site WithWithwith respectVHHs to getting dominant more chemical widespread species. in in the atmosphere, some some VHH VHH species species have have become become a a concernconcern to to atmospheric atmospheric scientists. scientists. Long-term Long-term monito monitoringring of of some some volatile volatile organic organic compounds compounds (VOCs), whichWith have VHHs important getting impacts impacts more on onwidespread the the global global in climate climate the atmosphere, or or are are radiative some gases, gases,VHH has hasspecies been been have carried carried become out out as as a partpartconcern of the to atmosphericAdvanced Global scientists. Atmospheric Atmospheric Long-term Gases Gases monito Experiment Experimentring of some (AGAGE) (AGAGE) volatile andorganic and its its subsidiary subsidiarycompounds network. network. (VOCs), Amongwhich have these important VOCs, 11 impacts VHH species, on the including global climate trichlorofluoromethane, trichlorofluoromethane, or are radiative gases, dichlorodifluoromethane, dichlorodifluoromethane, has been carried out as trichlorotrifluoroethane,trichlorotrifluoroethane,part of the Advanced Global dichlorotetrafluoroethan dichlorotetrafluoroethane, Atmospheric Gases Experimente, chlorodifluoromethane, chlorodifluoromethane, (AGAGE) and its tetrachloromethane, tetrachloromethane,subsidiary network. bromomethane,bromomethane,Among these VOCs, monochloromethane, monochloromethane, 11 VHH species, dichloromethanincluding dichloromethane, trichlorofluoromethane,e, trichloromethane, trichloromethane, dichlorodifluoromethane, and and tetrachloroethene, tetrachloroethene, weretrichlorotrifluoroethane, observed in this study. dichlorotetrafluoroethan Comparisons of of mixing mixinge, ratios ratioschlorodifluoromethane, of of the the 11 11 VHHs VHHs in in the the tetrachloromethane, study study area area against against theirtheirbromomethane, global global background background monochloromethane, levels levels fr fromom AGAGE AGAGE dichloromethan are are shown showne, in intrichloromethane, Table Table 22.. Mixing ratiosand tetrachloroethene, of thethe 1111 VHHs,VHHs, includingincludingwere observed 77 controlledcontrolled in this ODSstudy. ODS in Comparisons China,in China, were were all of highermixing all higher than ratios their than of globalthe their 11 backgroundVHHsglobal in background the levels. study Inarea levels. particular, against In particular,thetheir mixing global ratiosthe background mixing of dichloromethane, ratios levels of frdichloromethane,om trichloromethane,AGAGE are showntrichloromethane, and in tetrachloroethene Table 2. Mixingand tetrachloroethene inratios this studyof the were11 inVHHs, 42.34, this study14.17,including andwere 25.737 42.34, controlled times 14.17, higher ODSand than25.73in China, their times global werehigher backgroundall th higheran their than levels,global their respectively,background global background suggestinglevels, respectively, thatlevels. there In particular, the mixing ratios of dichloromethane, trichloromethane, and tetrachloroethene in this were stronger source emissions for these three VHHs in the study area [36]. Although the mixing ratios ofstudy monochloromethane were 42.34, 14.17, and and chlorodifluoromethane 25.73 times higher th inan this their study global were background as high as 1413.6 levels, and respectively, 1589.3 pptV, respectively, they have relatively lower levels compared with their global background levels (540.51 and Atmosphere 2020, 11, 1021 7 of 19

231.16 pptV, respectively). As controlled ODS in China, the mixing ratios of trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, 1,1,2-trichlorotrifluoroethane, tetrachloromethane, and bromomethane were comparable with their global background levels. The concentrations of these 11 VHHs in the study area compared with other national and international cities are also shown in Table2 to provide context to their pollution status in Beijing. The mixing ratio of monochloromethane in the study area was higher than the average mixing ratio of monochloromethane in 45 Chinese cities, as well as Bristol (UK), but lower than in Changsha (China). The mixing ratio of dichloromethane in the study area was higher than the average concentration of dichloromethane in 45 Chinese cities, as well as Changsha (China), Bristol (UK), Philadelphia (USA), and Marseille (France), but lower than in Tianjin (China) and Shenyang (China). Likewise, the mixing ratio of trichloromethane in the study area was higher than the average mixing ratio of trichloromethane in 45 Chinese cities, as well as Shenyang (China), Changsha (China), Bristol (UK), Philadelphia (USA), and Marseille (France), but lower than in Tianjin (China). In contrast, the mixing ratio of tetrachloroethene was lower than the average mixing ratio of tetrachloroethene in 45 Chinese cities, as well as Shenyang (China), Tianjin (China), Philadelphia (USA), and Marseille (France), but higher than in Changsha (China) and Bristol (UK). As controlled ODS in China, the mixing ratios of CFCs in this study, including trichlorofluoromethane, dichlorodifluoromethane, trichlorotrifluoroethane, and dichlorotetrafluoroethane, were slightly higher than in the other Chinese cities and selected international ones, but lower than in industrial cities, such as Shenyang. As the major substitute for dichlorodifluoromethane, the mixing ratio of chlorodifluoromethane in this study was much higher than in the other Chinese cities and selected international ones. It might be because the sampling time was in summer in this study, which could lead to active air-conditioning and refrigerating, and rapid residue discharge from foam products under high temperature [37]. The higher population density in Beijing could generate a greater demand for air conditioning, leading to larger chlorodifluoromethane emissions [37]. The mixing ratios of tetrachloromethane and bromomethane were comparable with their mixing ratios in other national and international cities.

3.2. Temporal Variations

3.2.1. Daily Variations The daily averages of the total mass concentrations of the 23 VHHs over the study period had two peaks (Figure4). The first peak occurred on 26 August, with a daily concentration of 35.36 µg/m3, while the second peak occurred on 30 August, with a daily concentration of 41.30 µg/m3. The occurrence of these peaks indicates that low wind speed, high temperature, high RH, and weak ultraviolet radiation might lead to the accumulation of VHHs in the ambient air (Figure5). After 1–2 September, the daily average concentration of VHH species declined markedly, indicating that high wind speed is conducive to VHHs diffusion (Figure5). Variations in the daily concentrations of the 23 VHH species are shown in Figure6. It can be seen that the daily average concentrations of chloroalkanes varied in a similar manner to the total concentration of VHHs, while others species had different trends. Atmosphere 2020, 11, 1021 8 of 19

Table 2. Comparisons of concentrations of 11 volatile halogenated hydrocarbons (VHHs) in the study area against their global background levels from the Advanced Global Atmospheric Gases Experiment (AGAGE) and levels from other studies.

Site Year CFC-11 * CFC-12 * CFC-113 * CFC-114 * HCFC-22 * CCl4 * CH3Br * CH3Cl CH2Cl2 CHCl3 C2Cl4 Reference Beijing, China 2012/08–2012/09 391.10 710.80 95.90 22.40 1589.30 135.60 15.40 1413.60 1883.70 168.30 64.60 This study Beijing, China 2010/10 377.00 649.00 99.00 18.00 977.00 ------[38] Tianjin, China 2008/04–2009/01 340.64 540.18 - 22.68 - 170.94 8.96 - 3476.71 250.87 122.25 [39] Changsha, China 2007/12–2008/11 288.00 654.00 108.00 24.00 - 153.00 21.00 1929.00 929.00 120.00 52.00 [8] Shenyang, China 2008/04–2009/01 578.07 1915.45 - 11.67 - 219.57 14.86 - 5333.48 132.85 82.67 [39] Shanghai, China 2010/10 248.00 593.00 74.00 17.00 1026.00 - [38] Guangzhou, China 2010/10 241.00 560.00 71.00 17.00 409.00 ------[38] 45 Cities, China 2001/01–2001/02 284.00 564.00 90.00 15.00 220.00 114.00 13.00 952.00 226.00 48.00 129.00 [40] 46 Cities, China 2010/10–2010/11 268.00 558.00 78.00 17.00 508.00 ------[38] Bristol, UK 2004/10–2005/12 255.30 545.10 - - 314.80 92.20 16.10 534.40 289.40 39.00 34.10 [41] Philadelphia, USA 2001/02 273 567 81 15 - 98 - - 97 27 116 [40] Marseille, France 2001/06–2001-07 288 564 84 16 - 107 - - 251 25 276 [40] Five background 2011/01–2012/12 239.50 536.50 74.66 - 232.10 ------[42] stations, China Trinidad Head, 2012 236.26 527.48 74.03 16.35 231.16 84.75 7.33 540.51 44.49 11.88 2.51 AGAGE California ** CFC-11: trichlorofluoromethane; CFC-12: dichlorodifluoromethane; CFC-113: trichlorotrifluoroethane; CFC-114: dichlorotetrafluoroethane; HCFC-22: chlorodifluoromethane. “-”: no data. *: controlled ozone-depleting substances in China. **: data are from the AGAGE network in 2012. The sites were chosen for comparison due to their similar latitudes to our sampling. Atmosphere 2020, 11, x FOR PEER REVIEW 9 of 19 Atmosphere 2020, 11, x FOR PEER REVIEW 9 of 19

3.2.3.2. TemporalTemporal VariationsVariations

3.2.1.3.2.1. DailyDaily VariationsVariations TheThe dailydaily averagesaverages ofof thethe totaltotal massmass concentratioconcentrationsns ofof thethe 2323 VHHsVHHs overover thethe studystudy periodperiod hadhad 3 twotwo peakspeaks (Figure(Figure 4).4). TheThe firstfirst peakpeak occurredoccurred onon 2626 August,August, withwith aa dailydaily concentrationconcentration ofof 35.3635.36 µg/mµg/m3,, 3 whilewhile thethe secondsecond peakpeak occurredoccurred onon 3030 AugustAugust,, withwith aa dailydaily concentrationconcentration ofof 41.3041.30 µg/mµg/m3.. TheThe occurrenceoccurrence ofof thesethese peakspeaks indicatesindicates thatthat lowlow windwind speed,speed, highhigh temperature,temperature, highhigh RH,RH, andand weakweak ultravioletultraviolet radiationradiation mightmight leadlead toto thethe accumulationaccumulation ofof VHHsVHHs inin thethe ambientambient airair (Figure(Figure 5).5). AfterAfter 1–21–2 September,September, thethe dailydaily averageaverage concentrationconcentration ofof VHHVHH speciesspecies declineddeclined markedly,markedly, indicatingindicating thatthat highhigh windwind speedspeed isis conduciveconducive toto VHHsVHHs diffusiondiffusion (Figure(Figure 5).5). VariationsVariations inin thethe dailydaily concentrationsconcentrations ofof thethe 2323 VHHVHH speciesspecies areare shownshown inin FigureFigure 6.6. ItIt cancan bebe seenseen thatthat thethe dailydaily averageaverage concentrationsconcentrations ofof chloroalkanesAtmospherechloroalkanes2020, 11 variedvaried, 1021 inin aa similarsimilar mannermanner toto thethe totatotall concentrationconcentration ofof VHHs,VHHs, whilewhile othersothers speciesspecies9 hadhad of 19 differentdifferent trends.trends.

FigureFigure 4.4. DailyDailyDaily variationvariation variation ofof of thethe the massmass mass concentrationsconcentrations concentrations ofof volatilevolatile of volatile halogenatedhalogenated halogenated hydrocarbonshydrocarbons hydrocarbons inin thethe in the studystudy area. area.

Figure 5. Daily variation of the mass concentrations of volatile halogenated hydrocarbons and meteorological factors in the study area. Atmosphere 2020, 11, x FOR PEER REVIEW 10 of 19

Figure 5. Daily variation of the mass concentrations of volatile halogenated hydrocarbons and meteorological factors in the study area. Atmosphere 2020, 11, 1021 10 of 19

Figure 6. Daily variation in average mass concentration concentration of selected selected volatile volatile halogenated halogenated halocarbons. halocarbons. (a): chlorofluorocarbons; chloroﬂuorocarbons; (b (b):): hydrochlorofluorocarbon; hydrochloroﬂuorocarbon; (c): ( c):chloroalkanes; chloroalkanes; (d): (dchloroalkenes;): chloroalkenes; (e): (chlorinatede): chlorinated benzenes; benzenes; (f): bromohydrocarbons. (f): bromohydrocarbons.

The daily average concentrations of the fourfour CFCs,CFCs, including trichlorofluoromethane,trichlorofluoromethane, dichlorodifluoromethane,dichlorodifluoromethane, dichlorotetrafluoroethane,dichlorotetrafluoroethane, and and 1,1,2-trichlorotrifluoroethane, 1,1,2-trichlorotrifluoroethane, did notdid show not obviousshow obvious temporal temporal variations variations (Figure6 a).(Figure Since 6a). these Since CFCs these are controlled CFCs are ODS controlled under theODS agreement under the of theagreement “Montreal of Protocolthe “Montreal on Substances Protocol that on DepleteSubstances the Ozonethat Deplete Layer”, the China Ozone has completelyLayer”, China banned has consumptioncompletely banned and production consumption of these and fourproduction CFCs since of these 1 January, four 2010.CFCs Thesince detection 1 January, of these 2010. CFCs The in the study area indicates that more strict environmental management countermeasures need to be taken to prevent such pollution. Emission sources of these four CFCs appear to be stable in the study area given their small variations in daily average concentrations over the study period. Atmosphere 2020, 11, x FOR PEER REVIEW 11 of 19

Atmospheredetection2020 of ,these11, 1021 CFCs in the study area indicates that more strict environmental management11 of 19 countermeasures need to be taken to prevent such pollution. Emission sources of these four CFCs appear to be stable in the study area given their small variations in daily average concentrations over the studyIn contrast, period. the daily average concentrations of chlorodifluoromethane varied markedly (Figure6b), whichIn couldcontrast, reflect the daily that average leakage concentrations of refrigerants of is chlorodifluoromethane a source of VHHs in varied the study markedly areabecause (Figure 6b),chlorodifluoromethane which could reflect is that used leakage in air conditioners,of refrigerants as is well a source as industrial of VHHs and in commercial the study area refrigerators because chlorodifluoromethanein China. is used in air conditioners, as well as industrial and commercial refrigerators in China.The daily average concentrations of dichloromethane varied most among the 23 VHHs. TheThe maximum daily average concentration concentrations of dichloromethane of dichloromethane occurred varied on 30most August, among andthe 23 the VHHs. minimum The maximumconcentration concentration on 2 September, of dichloromethane representing occurre 1.45 andd on 0.28 30 August, times itsand daily the minimum average concentration,concentration onrespectively 2 September, (Figure representing6c). As can 1.45 be seen and from0.28 times the daily its daily variations average of dichloromethane,concentration, respectively its concentrations (Figure were6c). As relatively can be seen high from and the unstable, daily variations indicating of dichloromethane, that there are local its emissionconcentrations sources were close relatively to the highsampling and unstable, site. indicating that there are local emission sources close to the sampling site. The daily average concentrations of tetrachloroethene changed most significantlysignificantly among the chlorinated hydrocarbonshydrocarbons (Figure (Figure6d); 6d); its highestits highest and and lowest lowest values values were 1.88were and 1.88 0.19 and times 0.19 its times average its valueaverage over value the studyover the period. study Daily period. average Daily concentrations average concentrations of 1,4-dichlorobenzene of 1,4-dichlorobenzene varied most amongvaried mostthe chlorinated among the benzeneschlorinated (Figure benzenes6e), with(Figure highest 6e), wi andth highest lowest and values lowest being values 2.19 being and 0.28 2.19 times and 0.28 its timesaverage its value average over thevalue study over period. the study For bromohydrocarbons, period. For bromohydrocarbons, the daily average the concentrations daily average of concentrationstribromomethane of tribromomethane varied more than thosevaried of more bromomethane than those of (Figure bromomethane6f). (Figure 6f). 3.2.2. Diurnal Variations 3.2.2. Diurnal Variations The diurnal variations of the mass concentration of VHHs in the study area are shown in The diurnal variations of the mass concentration of VHHs in the study area are shown in Figures Figures7 and8. The total mass concentration of VHHs had a “V-Shaped” trend, being higher in 7 and 8. The total mass concentration of VHHs had a “V-Shaped” trend, being higher in the morning the morning and at night, and lower at noon. Maxima of the total VHHs concentrations occurred and at night, and lower at noon. Maxima of the total VHHs concentrations occurred within the period within the period 8:30–9:00 a.m., while minima occurred during 1:30–2:00 p.m., and then increased 8:30–9:00 a.m., while minima occurred during 1:30–2:00 p.m., and then increased again slowly (Figure again slowly (Figure7). Aside from fluorodichloromethane, tetrachloroethene, 1,4-dichlorobenzene, 7). Aside from fluorodichloromethane, tetrachloroethene, 1,4-dichlorobenzene, 1,3-dichlorobenzene, 1,3-dichlorobenzene, and tribromomethane, the concentrations of most VHH species had similar and tribromomethane, the concentrations of most VHH species had similar diurnal variations with diurnal variations with the total VHHs concentrations (Figure8). the total VHHs concentrations (Figure 8).

Figure 7. DiurnalDiurnal variation variation of of the the average average mass mass concentration concentration volatile halogenated halocarbons in the study area.

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FigureFigure 8.8. DiurnalDiurnal variation variation in averagein average mass concentrationmass concentration of selected of volatileselected halogenated volatile halogenated halocarbons. halocarbons.(a): chloroﬂuorocarbons; (a): chlorofluorocarbons; (b): hydrochloroﬂuorocarbon; (b): hydrochlorofluorocarbon; (c): chloroalkanes; (c): chloroalkanes; (d): chloroalkenes; (d): chloroalkenes;(e): chlorinated (e benzenes;): chlorinated (f): bromohydrocarbons. benzenes; (f): bromohydrocarbons.

TheThe mass mass concentration concentration of of chlorodifluoromethane chlorodiﬂuoromethane dec decreasedreased dramatically dramatically from from 8:30 8:30 to to 9:00 9:00 a.m. a.m. toto a a minimum minimum value value between between 1:30 1:30 and and 2:00 2:00 p.m., p.m., and and then then increased increased slightly slightly until until 6:00–6:30 6:00–6:30 p.m., p.m., but decreasedbut decreased again again until until 10:00–10:30 10:00–10:30 p.m. p.m. (Figure (Figure 8b).8b). The The mass mass concentration concentration of of tetrachloroethylene alsoalso showed showed a a “V-shaped” “V-shaped” trend, trend, but but with with its its maximum maximum occurring occurring between between 10:00 10:00 and and 10:30 10:30 p.m. p.m. (Figure(Figure 88d).d). Mass concentrations concentrations of of 1,4-dichlorobe 1,4-dichlorobenzenenzene increased increased continuously continuously from from the the morning morning to night,to night, with with greatest greatest increases increases occurring occurring between between 8:30 and 8:30 9:00 and a.m. 9:00 and a.m. 1:30 and 2:00 1:30 p.m., and as 2:00 well p.m., as 6:00as well and as 6:30 6:00 andp.m. 6:30and p.m. 10:00 and and 10:00 10:30 and p.m. 10:30 (Figure p.m. (Figure8e). The8e). mass The massconcentrations concentrations of 1,3- of dichlorobenzene1,3-dichlorobenzene had hadan inverse an inverse diurnal diurnal variation variation with with respect respect to the to thetotal total mass mass concentrations concentrations of VHHsof VHHs (Figure (Figure 8e),8 e),producing producing an an“Inverted “Inverted V-Shaped V-Shaped”” trend, trend, with with lower lower values values in the in morning the morning and atand night, at night, and highest and highest values valuesbetween between 6:00 and 6:00 6:30 and p.m. 6:30 We p.m.speculate We that speculate there may that be there continuous may be emissioncontinuous of emission1,3-dichlorobenzene, of 1,3-dichlorobenzene, resulting in resulting accumulation in accumulation of 1,3-dichlorobenzene of 1,3-dichlorobenzene during the during day. Thethe day.massThe concentrations mass concentrations of tribromomethane of tribromomethane increased increased from from 8:30 8:30to 9:00 to 9:00 a.m. a.m. to to1:30 1:30 to to 2:00 2:00 p.m., p.m., thenthen decreaseddecreased until until 6:00–6:30 6:00–6:30 p.m., p.m., before before increasing increasi tong its highestto its highest values aroundvalues 10:00–10:30around 10:00–10:30 p.m. (Figure p.m.8f). (FigureThe 8f). diurnal variations of VHH concentrations in the ambient air are inﬂuenced by many factors, suchThe as emissiondiurnal variations source characteristics, of VHH concentrations meteorological in the ambient conditions, air are and influenced rates of local by many atmospheric factors, such as emission source characteristics, meteorological conditions, and rates of local atmospheric photochemical reactions [43]. In the morning, the mass concentrations of VHHs were maintained at

Atmosphere 20202020,, 1111,, 1021x FOR PEER REVIEW 13 of 19

a high level because of the atmospheric stability, a low boundary-layer height, and anthropogenic photochemicalemissions. Then, reactions the mass [43 concentrations]. In the morning, of VH theHs mass reached concentrations the lowest ofmass VHHs concentration were maintained between at a1:30 high and level 2:00 because p.m. as the of the temperature, atmospheric the stability, photochemical a low boundary-layerreaction, and wind height, speed and increased anthropogenic (Figure emissions.5), which accelerates Then, the massthe consumption concentrations and of VHHsdiffusion reached of VHHs. the lowest Afterwards, mass concentration as the temperature, between 1:30atmospheric and 2:00 p.m.boundary as the layer, temperature, and wind the speed photochemical decreased, reaction, the mass and concentrations wind speed increasedof VHHs (Figureincreased5), whichgradually. accelerates the consumption and diﬀusion of VHHs. Afterwards, as the temperature, atmospheric boundary layer, and wind speed decreased, the mass concentrations of VHHs increased gradually. 3.3. Source Apportionment 3.3. Source Apportionment Figure 9 shows the main sources of volatile halogenated hydrocarbons in ambient air in the studyFigure area and9 shows the contributions the main sources of individual of volatile comp halogenatedounds. Seven hydrocarbons factors were in ambient finally identified air in the studyusing areaPMF and 5.0. the contributions of individual compounds. Seven factors were finally identified using PMF 5.0.

Figure 9. Main sources of volatile halogenated hydrocarbo hydrocarbonsns in ambient air in the study area and the contributions of individual compounds.compounds.

Factor 1 was characterized by high loadings of tetrachloroethene (58.89%). Tetrachloroethene is mainly used as industrial cleaning solvents in the electronicelectronic industryindustry [[25,44].25,44]. So, we concluded that factor 1 described emissionsemissions fromfrom solventssolvents usageusage inin thethe electronicelectronic industry.industry. Factor 2 was characterized by high loadings of chlorodiﬂuoromethanechlorodifluoromethane (53.40%). ChlorodiﬂuoromethaneChlorodifluoromethane is is a majora major refrigerant refrigerant replacement replacement and widely and used widely in commercial used in refrigerationcommercial andrefrigeration refrigeration and transportrefrigeration [43 ].transport So, we concluded [43]. So, we that concluded factor 2 describedthat factor emissions2 described from emissions refrigerants. from refrigerants.Factor 3 was characterized by high loadings of 1,4-dichlorobenzene (71.63%). 1,4-dichlorobenzene is usedFactor mainly 3 aswas a fumigant characterized for the controlby high of moths, loadings molds, of and 1,4-dichlorobenzene mildews, and as a space(71.63%). deodorant 1,4- dichlorobenzene is used mainly as a fumigant for the control of moths, molds, and mildews, and as

Atmosphere 2020, 11, 1021 14 of 19 Atmosphere 2020, 11, x FOR PEER REVIEW 14 of 19 fora space toilets deodorant and refuse for containerstoilets and [refuse35]. So, containers we concluded [35]. So, that we factor concluded 3 described that factor emissions 3 described from fumigantemissions usage.from fumigant usage. Factor 4 4 was was characterized characterized by by high high loadings loadings of chlorobenzene, of chlorobenzene, monochloroethane, monochloroethane, and andtrichloromethane. trichloromethane. Chlorobenzene Chlorobenzene (93.17%) (93.17%) is used is used as a assolvent a solvent for forsome some pesticide pesticide formulations, formulations, to todegrease degrease automobile automobile parts, parts, and and as as a achemical chemical in intermediatetermediate to to make make several several other other chemicals chemicals [45]. [45]. Monochloroethane (63.80%) is used in the production of cellulose, dyes, medicinal drugs, and other commercial products,products, and and as as a solventa solvent and and refrigerant refrigerant [45 ].[45]. Trichloromethane Trichloromethane (58.49%) (58.49%) is formerly is formerly used asused an as inhaled an inhaled anesthetic anesthetic during during surgery, surgery, a solvent, a solv andent, inand the in production the production of the of refrigerant the refrigerant freon freon [36]. So,[36]. we So, concluded we concluded that factorthat factor 4 described 4 described emissions emissi fromons from solvents solvents usage usage and and industrial industrial processes. processes. Factor 5 was characterized by high loadings of CFCs and tetrachloromethane.tetrachloromethane. CFCs are mainly used asas refrigerantsrefrigerants in in cooling cooling appliances appliances and and air conditioning, air conditioning, whereas whereas tetrachloromethane tetrachloromethane is mainly is usedmainly as used feedstock as feedstock for CFC productionfor CFC production [44]. Although [44]. Although CFCs and CFCs tetrachloromethane and tetrachloromethane were supposed were tosupposed be entirely to be phased-out entirely phased-out in 2010 in in China, 2010 thesein China, species these produced species produced before 2010 before are still2010 stored are still in equipmentstored in equipment and can leak and into can theleak environment into the environm [25]. So,ent we [25]. concluded So, we concluded that factor that 5 described factor 5 emissionsdescribed fromemissions leakage from of leakage CFCs banks. of CFCs banks. Factor 6 6 was was characterized characterized by by high high loadings loadings of dichloromethane, of dichloromethane, dichloroethane, dichloroethane, and anddichloropropane. dichloropropane. Chloroalkanes Chloroalkanes are widely are widely used used as assolvents solvents and and in inthe the production production of of other chemicals. Dichloromethane is is well known as a fe feedstockedstock for foam plastic products, metal cleaning, and other solvent uses uses [44]. [44]. Dichloroethane Dichloroethane and and dich dichloropropaneloropropane are are also also widely widely used used in inindustry industry as assolvents. solvents. So, we So, concluded we concluded that factor that 6 factor describe 6 describedd emissions emissions from solvents from usage solvents and usage industrial and industrialprocesses. processes. Factor 7 was characterized by high loadings of trichloroethene.trichloroethene. Trichloroethene is widely used in electronicelectronic andand textiletextile industriesindustries asas aa solventsolvent andand degreaserdegreaser [[44].44]. So, we concluded that factor 7 described emissions from solventssolvents usageusage inin thethe electronicelectronic andand textiletextile industries.industries. Average contributionscontributions ofof eacheach factor factor to to the the total total volatile volatile halogenated halogenated hydrocarbons hydrocarbons are are shown shown in Figurein Figure 10. Since10. Since factor factor 1, factor 1, factor 4, factor 4, 6,factor and factor 6, and 7 are factor related 7 are to solventsrelated usage,to solvents their contributionsusage, their arecontributions summed asare the summed contribution as the ofcontribution solvents usage of solv andents industrial usage and processes industrial to volatileprocesses halogenated to volatile hydrocarbons.halogenated hydrocarbons. It can be seen thatIt can solvents be seen usage that andsolv industrialents usage processes and industrial (51.73%) processes is a major (51.73%) contributor is a inmajor the contributor study area, in followed the study by area, leakage followed of CFCs by banksleakage (21.92%). of CFCs Refrigerantsbanks (21.92%). and Refrigerants fumigant usage and contributedfumigant usage 17.31% contributed and 9.04%, 17.31% respectively. and 9.04%, respectively.

Figure 10.10. Source contributions to the total volatile halogenatedhalogenated hydrocarbons in ambient air in the study area. 3.4. Health Risk Assessment 3.4. Health Risk Assessment According to the International Agency for Research on Cancer (IARC), chemicals are divided into ﬁveAccording categories to the (1, International 2A, 2B, 3, and Agency 4) based for Rese on theirarch carcinogenicityon Cancer (IARC), [35, 46chemicals]. Categories are divided 1, 2A, andinto 2Bfive are categories acknowledged (1, 2A, to2B, be 3, carcinogenic and 4) based to on humans. their carcinogenicity Hence, the carcinogenic [35,46]. Categories risk of seven 1, 2A, VHH and 2B are acknowledged to be carcinogenic to humans. Hence, the carcinogenic risk of seven VHH species belonging to these categories was assessed. The non-carcinogenic risk for adults in the study species belonging to these categories was assessed. The non-carcinogenic risk for adults in the study area was assessed for 11 VHH species whose RfC values could be obtained from the Integrated Risk area was assessed for 11 VHH species whose RfC values could be obtained from the Integrated Risk Information System. Information System.

Atmosphere 2020, 11, 1021 15 of 19

The parameters used for the carcinogenic risk assessment for these VHHs as well as for the non-carcinogenic risk assessment of the dominant 11 VHH species are shown in Tables3 and4, respectively. According to the US EPA document “EPA-540-R-070-002”, the acceptable value of Risk for a speciﬁc pollutant for an ordinary adult is 1 10 6 [47]. The Risk values for the seven carcinogenic × − VHHs varied from 6.43 10 8 to 8.04 10 5, with the Risk of trichloromethane, tetrachloromethane, × − × − 1,2-dichloroethane, and 1,4-dichlorobenzene being more than 1 10 6. 1,2-Dichloroethane had the × − highest Risk, with a Risk of 80.4 times 1 10 6, followed by trichloromethane with a Risk of 18.6 times × − 1 10 6, and 1,4-dichlorobenzene and tetrachloromethane with Risks of ﬁve–six times 1 10 6. Thus, × − × − trichloromethane, tetrachloromethane, 1,2-dichloroethane, and 1,4-dichlorobenzene in the ambient air posed relatively high carcinogenic risks to the long-term exposed populations in the study area.

Table 3. Carcinogenic risk assessment for 7 volatile halogenated hydrocarbons.

Exposure IARC Level Pollutant Concentration IUR/(m3/µg) Risk (Publication Year) (µg/m3) Dichloromethane 2B (1999) 6.43 1.0 10 8 6.43 10 8 × − × − Trichloromethane 2B (1999) 0.81 2.3 10 5 1.86 10 5 × − × − Tetrachloromethane 2B (1999) 0.84 6.0 10 6 5.04 10 6 × − × − 1,2-Dichloroethane 2B (1999) 3.09 2.6 10 5 8.04 10 5 × − × − Trichloroethene 2A (1995) 0.18 4.1 10 6 7.31 10 7 × − × − Tetrachloroethene 2A (1995) 0.43 2.6 10 7 1.12 10 7 × − × − 1,4-Dichlorobenzene 2B (1999) 0.54 1.1 10 5 5.89 10 6 × − × − IARC = International Agency for Research on Cancer; IUR = inhalation unit risk.

Table 4. Non-carcinogenic risk assessment for 11 volatile halogenated hydrocarbons.

Exposure Concentration Pollutant RfC (mg/m3) HQ (µg/m3) Monochloromethane 2.87 1.0 101 2.87 10 4 × × − Dichloromethane 6.43 6.0 10 1 1.07 10 2 × − × − Tetrachloromethane 0.84 1.0 10 1 8.40 10 3 × − × − Monochloroethane 0.15 1.0 101 1.54 10 5 × × − 1,2-Dichloropropane 3.09 4.0 10 3 5.94 10 1 × − × − 1,1-Dichloroethene 0.01 2.0 10 1 5.00 10 5 × − × − Trichloroethene 0.18 2.0 10 3 9.00 10 2 × − × − Tetrachloroethene 0.43 4.0 10 2 1.08 10 2 × − × − 1,4-Dichlorobenzene 0.54 8.0 10 1 6.75 10 4 × − × − Chlorodiﬂuoromethane 5.55 5.0 101 1.11 10 5 × × − Bromomethane 0.06 5.0 10 3 1.20 10 2 × − × − HI = 0.728 RfC = inhalation reference concentration; HQ = hazard quotient; HI = hazard index.

According to the US EPA, if the value of HQ for a speciﬁc pollutant is lower than 1, the pollutant has no obvious non-carcinogenic risk to humans. The HQ of the 11 VHH species varied from 1.54 10 5 to × − 5.94 10 1, while HI was 0.728. The result indicates that these VHHs had no obvious non-carcinogenic × − risk to the general population in the study area. Among the 11 VHH species, 1,2-dichloropropane had the highest HQ value (5.94 10 1), followed by trichloroethene (9.00 10 2). × − × − Huang et al. [48] determined values of Risk for trichloromethane and 1,4-dichlorobenzene in a primary school to be 6.5 10 7 and 1.6 10 7, respectively. Clearly, the values of Risk for × − × − trichloromethane and 1,4-dichlorobenzene in this study were 28 and 36 times higher, posing a far greater risk to residents in the study area. In contrast, the values of Risk for trichloroethene and tetrachloroethene for this study were comparable to those in ambient air in Nanjing [49], suggesting that these species do not pose a threat to local residents in Beijing or Nanjing. Atmosphere 2020, 11, 1021 16 of 19

Comparisons of non-carcinogenic risk assessments for nine volatile halogenated hydrocarbons in Liaoning Province [12] and this study are shown in Table5. Clearly, the HQ values of monochloromethane, tetrachloromethane, and 1,1-dichloroethene in this study were lower than in some cities of Liaoning Province, whereas the HQ values of 1,2-dichloropropane, tetrachloroethene, and bromomethane were mostly higher. No apparent diﬀerence between the two studies was observed for dichloromethane, monochloroethane, and trichloroethene.

Table 5. Comparison of non-carcinogenic risk assessments for nine volatile halogenated hydrocarbons in Liaoning Province [12] and this study.

Pollutant This Study Fushun Shenyang Anshan Huludao Monochloromethane 2.87 10 4 1.50 10 2 6.70 10 3 9.30 10 3 1.60 10 2 × − × − × − × − × − Dichloromethane 1.07 10 2 9.10 10 3 2.40 10 2 2.30 10 2 6.10 10 3 × − × − × − × − × − Tetrachloromethane 8.40 10 3 1.20 10 2 1.40 10 2 1.70 10 2 9.30 10 3 × − × − × − × − × − Monochloroethane 1.54 10 5 1.70 10 5 1.40 10 5 -- × − × − × − 1,2-Dchloropropane 5.94 10 1 2.87 10 4 2.87 10 4 2.87 10 4 2.87 10 4 × − × − × − × − × − 1,1-Dichloroethene 5.00 10 5 - 1.40 10 4 -- × − × − Trichloroethene 9.00 10 2 - 1.60 10 1 2.70 10 2 - × − × − × − Tetrachloroethene 1.08 10 2 1.30 10 4 7.90 10 3 1.80 10 3 - × − × − × − × − Bromomethane 1.20 10 2 1.10 10 3 2.90 10 3 -- × − × − × − “-”: no data.

Health risk assessments of VHHs in the ambient air in urban areas of China suggest that non-carcinogenic risks are at a relatively low level, but Risks for trichloromethane, tetrachloromethane, and 1,2-dichloroethane are relatively high. Given that there are few studies on the carcinogenic risk assessment of VHHs in China to date, it is crucial to carry out more health risk assessments of toxic VHHs in the near future.

4. Conclusions In this study, VOC samples were collected with SUMMA canisters in a typical urban area of Beijing. VHH species were determined using a cryogenic cold trap pre-concentration prior to GC-MS/FID analysis. Ambient levels, temporal variation, and sources of VHHs were determined for the study area, and health risks of selected toxic and hazardous VHH species were assessed. The results showed that the mean and the range of daily total mass concentrations of the 23 VHHs were 30.53 and 13.45–76.33 µg/m3, respectively. Among the 23 VHHs, 7 VHHs were controlled ozone-depleting substances in China. The average and range of the seven VHHs were 12.95 and 7.69–36.17 µg/m3, respectively, accounting for 42.43% of the total. Dichloroethane had the highest concentrations, followed by chlorodifluoromethane, making chloroalkanes the main VHH constituent in the study area. Compared with other national and international cities, the concentrations of the selected 11 VHHs in the study area, including 7 controlled ODS in China, were relatively higher. Diurnal variation in the total mass concentrations of the 23 VHHs was marked by higher levels in the morning and evening, and lower levels at noon. Solvents usage and industrial processes, leakage of CFCs banks, refrigerants, and fumigant usage were the main sources of VHHs in the study area. Health risk assessment showed that four VHH species, including trichloromethane, tetrachloromethane, 1,2-dichloroethane, and 1,4-dichlorobenzene, posed potential carcinogenic risks to the exposed populations in the study area. None of the selected 11 VHH species posed appreciable non-carcinogenic risks to exposed populations. Therefore, it is imperative to take effective countermeasures to control VHH emissions in Beijing. For example, it is recommended that the construction and improvement of VHH emission inventories for key sources should be promoted nationwide, and not only the total amount but also the toxic VHHs should be included in the emission inventories, in order to lay the foundation for accurate source apportionment of ambient VHHs, as well as for the identification and refined control of key sources of VHHs. Atmosphere 2020, 11, 1021 17 of 19

Author Contributions: Conceptualization, H.L.; methodology, H.L.; formal analysis, Y.J., L.X. and C.W.; investigation, L.L., F.B., Y.Y. and Y.C.; writing—original draft preparation, Y.J. and L.X.; writing—review and editing, H.L. and Y.J.; validation: D.X., J.D., Y.Z., X.W. and W.Z.; visualization, H.Z. and L.M. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the National Key Research and Development Program of China (No. 2019YFC0214501), the Special Research Project for the National Environmental Protection Public Welfare Industry of China (No. 201009032, No. 201409005), and the National Key Technology Support Program (No. 2014BAC23B01). Acknowledgments: The authors would like to express special thankfulness to Bai Zhipeng, Geng Chunmei, and Xue Zhigang from the Chinese Research Academy of Environmental Sciences for their support to VOCs sampling. They also acknowledge Shao Min and Lu Sihua from Beijing University for their support to the instrumental analysis of VOCs samples. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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