Determination of Particle-associated Polycyclic Aromatic Hydrocarbons in Urban Air of Beijing by GC/MS

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1 2007 The Japan Society for Analytical Chemistry 667 Determination of Particle-associated Polycyclic Aromatic Hydrocarbons in Urban Air of Beijing by GC/MS Li-Bin LIU,* Yuki HASHI,*, ** Min LIU,* Yanlin WEI,* and Jin-Ming LIN* *State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P. O. Box 2871, Beijing , China **Shimadzu (Hong Kong) Limited, Beijing Office, Analytical Applications Center 14F No. 16, Chao Yang Men Wai Street, Life Tower Chao Yang District, Beijing , China Particle-associated polycyclic aromatic hydrocarbons (PAHs) collected in urban air of Beijing were studied using a gas chromatograph mass spectrometer (GC/MS). The average concentration of particle-associated PAHs measured in this work was in the range from to ng/m 3, which suggested a serious pollution level of PAHs in Beijing. The results also showed that the concentration of PAHs in the winter was distinctly higher than that in summer and spring. Benzo(a)pyrene (BaP) and benzo(a)pyrene-equivalent carcinogenic power (BaPE) were adopted to evaluate the PAHs pollution state at the sampling site. Through some diagnostic ratios, it can be concluded that traffic exhaust, especially vehicles with diesel engines, and domestic coal-burning heaters might have a prominent contribution to the PAHs concentration. (Received January 10, 2007; Accepted February 21, 2007; Published June 10, 2007) Introduction There has been growing concern about the potentially harmful effects of toxic agents distributed in the atmosphere on human health. It is well known that among these toxic agents, polycyclic aromatic hydrocarbons (PAHs) pose a great threat to human health. PAHs are a class of several hundred individual compounds containing at least two condensed rings. They exist in the atmosphere in both the vapor and particulate phases. Low-molecular-weight PAHs tend to be more concentrated in the vapor-phase, while those with higher molecular weight are often associated with particulates. PAHs are products of incomplete combustion and the pyrolysis of fossil fuels and other organic materials from natural and anthropogenic sources. They are present in the atmosphere due to emissions from gasoline- and diesel-powered vehicles, municipal and commercial incinerators, residential heating systems that combust such fuels as coal, wood, gas and oil, various industrial processes and volatilization from polluted grounds. 1 5 The main concern of PAHs is that they show adverse effects on health (carcinogenic and/or mutagenic activity) 6,7 and the ecosystem. 8 Due to the toxicity of PAHs in ambient air, many investigations have been carried out for the determination of their concentrations and mutagenity in airborne particulate matter. Various techniques have been developed for the determination of PAHs in airborne particulate matter. Chromatographic techniques, such as GC, HPLC coupled with fluorescence, UV, FID and MS detectors are the most frequently used Prior to a determination, the To whom correspondence should be addressed. jmlin@mail.tsinghua.edu.cn Present address: Department of Chemistry, Tsinghua University, Beijing , China. extraction of filters is always required by these techniques and, generally, Soxhlet and ultrasonic extractions are the most selective ones To help identify the major emission sources responsible for adverse health effects, a comprehensive survey of atmospheric contaminants from a variety of sources has been performed worldwide. In China, many studies have been conducted to determine atmospheric PAHs in some main cities, including Guangzhou, Hong Kong and Shenyang However, in Beijing, one of the biggest cities of China, not so much attention has been paid to determining the PAHs distributed in the urban atmosphere, whereas a few experiments have been performed so far With the rapid growth of industrial activities, population and traffic density (e.g. more than 15 million inhabitants and 2.5 million automotive vehicles), Beijing is really facing serious air-pollution problems. According to a report of National Bureau of Statistics of China (NBSC) in 2004, the annual coal consumption of Beijing was over 42 Mt, and it was recognized to be a major source of aerosol. These days, Beijing city is still under drastic development and especially is preparing the Olympic Games in 2008; various construction activities are ongoing, which inevitably exacerbates Beijing s air-pollution problems. Therefore, it is very important to conduct more detailed investigations on PAHs in the Beijing urban area and to track changes of the ambient air quality. Here, we present a report on the determination of 16 PAH associated with atmospheric particulate matter collected during different seasons in the Beijing urban area. All of the collected samples were pretreated by ultrasonic extraction and rotary evaporation, and then analyzed by GC/MS. Our results clearly show that the concentration of PAHs depends on the weather and season; we also wish that this study could offer aid in regulatory actions of improving the air quality in Beijing.

2 668 ANALYTICAL SCIENCES JUNE 2007, VOL. 23 Table 1 Typical retention time and m/z values of quantification and confirmation ions of a 16 US EPA PAHs mixture Component Retention time/min Quantification ion (m/z) Confirmation ion (m/z) Nap , 102 Acy , 153 Ace , 153 Fle , 165 Ph , 176 An , 176 Fla , 200 Pyr , 200 BaA , 226 Chr , 226 Bbf , 250 Bkf , 250 BaP , 250 InP , 277 DBahA , 279 BghiP , 277 Experimental Sampling program Airborne particulates were collected at the Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences (RCEES, CAS), Beijing, using a high-volume air sampler at a flow rate of 700 L/min. Air was sampled in different seasons between December 2004 and August. Quartz fiber filters were replaced every day. After being dried in a desiccator in the dark, the filters were weighed, and then stored in a refrigerator ( 20 C) until use. Sampling site characteristic Beijing, the national political and cultural center, is one of the biggest cities in China, located in the North China. It is considered that PAH emission has been continuously increasing owing to rapid growth in the national economy and energy consumption. RCEES is situated in northwest Beijing, Haidian District, between East longitude and North latitude 40 00, being located in the urban area within 1.5 km from the Fourth Ring Road highway. The sampling site is on the rooftop (ca. 15 m height) of a four-story research building. There are also some other research building and residential areas in RCEES. Around RCEES, there are also three roads with high traffic, many little restaurants and some big university restaurants. Thus, the particulate levels at the site are mainly influenced by vehicle emission, stationary combustion sources and the wind direction. Chemicals and solvents All chemicals used were of analytical reagent or chromatographic grade. Acetone, acetonitrile and ethanol were obtained from J. T. Baker (Phillipsburg, NJ, USA). Benzene was obtained from Beijing Chemical Factory (China). Analytical-grade dimethyl sulfoxide (DMSO) was obtained from Shantou Xilong Chemical Factory (Guangdong, China). HPLC-grade water was obtained by the purification of deionized water through a Milli-Q system (Bedford, USA) with a 0.22-μm fiber filter. EPA 16 PAHs mix including fluorene (Fle), phenanthrene (Ph), anthracene (An), fluoranthene (Fla), naphthalene (Nap), Fig. 1 Total ion chromatograms (TIC) of standard PAHs at 0.3 μg/ml (lower chromatogram) and one real air sample (upper chromatogram). Multiple chromatograms (A, B, C, D and E) are used to show all of the PAHs. 1, Nap; 2, Acy; 3, Ace; 4, Fle; 5, Ph; 6, An; 7, Fla; 8, Pyr; 9, BaA; 10, Chr; 11, Bbf; 12, Bkf; 13, BaP; 14, InP; 15, DBahA; 16, BghiP. acenaphthene (Ace), acenaphthylene (Acy), chrysene (Chr), benzo(g,h,i)perylene (BghiP), benzo(k)fluoranthene (Bkf), benzo(a)anthracene (BaA), indeno(1,2,3-c,d)pyrene (InP), benzo(b)fluoranthene (Bbf), dibenzo(a,h)anthracene (DBahA), benzo(a)pyrene (BaP) and pyrene (Pyr) were purchased from Phentex Corp. (USA). Pretreatment of samples A detailed description of sample pretreatment is in publication by Tang. 28 Briefly, the process is described as follows. Each quarter of a filter was thoroughly cut into small pieces in a

3 669 Table 2 Mean and total concentrations (ng/m 3 ) of particle-associated PAHs in different months (mean ± SD) PAH Dec Mar. Apr. May Aug. Nap ± ± ± ± ± 0.25 Acy 2.31 ± ± ± ± ± 0.03 Ace 0.46 ± ± 0.15 ND ND ND Fle 2.28 ± ± ± ± ± 0.04 Ph ± ± ± ± ± 0.21 An 6.69 ± ± ± ± ± 0.04 Fla ± ± ± ± ± 0.43 Pyr ± ± ± ± ± 0.39 BaA ± ± ± ± ± 0.29 Chr ± ± ± ± ± 0.47 Bbf ± ± ± ± ± 1.22 Bkf ± ± ± ± ± 0.65 BaP ± ± ± ± ± 0.49 InP ± ± ± ± ± 0.86 DBahA 4.70 ± ± ± ± ± 0.12 BghiP ± ± ± ± ± 0.72 ΣPAH ± ± ± ± ± 5.88 SD, standard deviation. ND, not detected. n = 10. flask. After PAHs were extracted ultrasonically twice (each time for 15 min) with benzene/ethanol (3:1, v/v), the solution was filtered. Then, a 100-μl portion of DMSO was added before the filtrate was evaporated to dryness. The residue was dissolved in 900 μl of acetonitrile. After being filtered again, they were diluted 10 times with acetone, and then injected into the GC/MS system. GC/MS system for determination of PAHs The 16 PAHs were determined by using the GC/MS QP2010 instrument (Shimadzu, Japan). An RTX-5ms column ((5% phenyl)methylpolysiloxane; 0.25 mm i.d. 30 m with a film thickness of 0.25 μm; Restek Corporation, Bellefonte, PA, USA) was used for separation. The temperature of the capillary column was set at 90 C for the initial 1 min, increased to 180 C at 8 C/min, then increased to 280 C at 15 C/min for 12 min. The injection temperature was 260 C. Helium was used as the carrier gas. The quadrupole mass spectrometer was operated in the electron impact ion (EI) mode with a source temperature of 200 C. The electron energy was 70 ev. A quantitative analysis of PAHs was carried out by selecting a specific mass for each analyte, that is, the selected-ion monitoring (SIM) mode. Table 1 lists the typical retention times and m/z ratios of the quantification and confirmation ions for all PAHs. Results and Discussion Quality control and assurance Quantifications of PAHs were conducted according to the retention times and peak areas of the calibration standards. Calibration curves were established throughout the range of μg/ml with correlation coefficients from to The limits of detection (LODs) were obtained by injecting a standard mixture, and were calculated with the signal-to-noise ratio (S/N) 3 in the SIM mode. The LODs of 16 PAHs were in the range of ng/ml, depending on the type of PAHs. Analysis of PAHs The total ion chromatograms (TIC) of standard PAHs at 0.3 μg/ml and one real air sample are shown in Fig. 1. Table 2 gives the mean and total concentrations of the Fig. 2 Profiles of the mean particle-associated individual PAH concentrations during different months in urban air at selected sampling sites. 1, Nap; 2, Acy; 3, Ace; 4, Fle; 5, Ph; 6, An; 7, Fla; 8, Pyr; 9, BaA; 10, Chr; 11, Bbf; 12, Bkf; 13, BaP; 14, InP; 15, DBahA; 16, BghiP. particle-associated PAHs during different months in the Beijing urban. The mean concentration and standard deviation (SD) were calculated using 10 raw data randomly collected from that of the data obtained in one entire month. The SD for the PAHs concentration observed in the present work was quite high. This result suggested an extreme variation of the PAHs concentration during every month; also, they strongly depended on the atmospheric system, i.e. rain, sunlight, snow, etc. Profiles of the mean particle-associated individual PAHs concentrations during different months are shown in Fig. 2. The concentrations of PAHs found in the winter (December and March) were much higher than in the spring (April and May) and in the summer (August), respectively. The high PAHs content in the winter was relatively due to domestic coalburning heaters in Beijing. In addition, the rush-hour traffic with diesel-engine vehicles in Beijing and from some cities nearby partly contributed to the PAHs concentration. Considering the seasonal variation, it may concern the stability of PAHs in the atmospheric system. The level of ozone in the winter is generally lower than in the spring and the summer, due

4 670 ANALYTICAL SCIENCES JUNE 2007, VOL. 23 Table 3 Comparison of total particle-associated PAHs (ng/m 3 ) in different areas Table 5 Diagnostic ratios calculated with the concentration of PAHs in different months Sampling site Sampling time Concentration of PAHs Kinds of PAHs Ref. Diagnostic ratio Dec Mar. Apr. May Aug. Kuala Lumpur Naples Tokyo Seoul Beijing May 2000 Sep July Winter, 2002 Dec Aug ± This study Table 4 Values of BaPE in different months (ng/m 3 ) Dec Mar. Apr. May Aug to less intensity of the sunlight. Therefore, the photochemical degradation of PAHs by ozone in the winter should be less than in the spring and summer seasons, respectively This hypothesis is very consistent with the results shown in Table 2. In December, the most abundant PAHs were Fla (60.88 ng/m 3 ). In March, except for the especially high concentration of Nap ( ng/m 3 ), Fla (13.34 ng/m 3 ) was also the most abundant PAHs among the other 15 PAHs. In April, May and August, the concentrations of PAHs were obviously lower. In these 3 months, Ace was not detected. Bbf was the most abundant PAHs in May and August (4.56 and 4.26 ng/m 3 ). In April, except for the somewhat higher concentration of Nap (16.54 ng/m 3 ), Bbf (9.00 ng/m 3 ) was also the most abundant PAHs among the other 15 PAHs. Considering the effect of weather on the PAHs concentrations, it was found that the concentrations of PAHs detected on snowy or rainy days were significantly lower than on others days in the same month. For example, in December 2004, the total concentrations of PAHs were found in the range of ng/m 3 on snowy days, whereas they were ng/m 3 on other days when there was no rain or snow. The mean concentrations of particle-associated PAHs (ng/m 3 ) found in Beijing in this investigation and in other different areas are compared in Table 3. It can be concluded that the concentration of the total PAHs in Beijing are much higher than in Tokyo, Seoul, Kuala Lumpur and Naples. The lowest concentration during the summer in Beijing is even higher than that in Tokyo, Seoul and Kuala Lumpur, revealing that air pollution in Beijing is serious. The BaP concentration and benzo(a)pyrene-equivalent carcinogenic power (BaPE) Because of the high carcinogenic property of BaP, limit values of 1 or 10 ng BaP per m 3 air are recommended or mandatory in various countries. The limit value recommended by WHO is 1 ng/m 3, while it is 10 ng/m 3 recommended in China. In this study, all the concentrations of BaP during different months exceed the WHO limit, especially in December. However, if we refer to the limit value recommended in China, it just exceeds that in December. Actually, except for BaP, other PAHs having 4 6 rings, such as BaA, Bbf, Bkf, InP and DBahA, also have carcinogenic potential. The benzo(a)pyrene-equivalent carcinogenic power InP/(InP + BghiP) BaP/BghiP Ph/(Ph + An) BaP/(BaP + Chr) (BaPE) 35 is an index that has been introduced for better denoting aerosol carcinogenicity related to the whole PAH fraction instead of the sole BaP. In fact, the latter is easily decomposed in reactive air parcels by light and oxidants and, when photochemical smog occurs, its concentration does not follow the PAH pattern. BaPE was calculated using the following formula, reported by Cecinato: 36 BaPE = BaA (Bbf + Bkf) BaP + DBahA InP Table 4 gives the values of BaPE in different months. It can be concluded that the air quality in August is the best, and then May, April, March and December. These results are consistent with the above discussion. Diagnostic ratios In recent years, an increasing number of studies 22,31,32 tried to use diagnostic ratios to help them to identify possible emission sources. The diagnostic ratios of this study were determined, and the values are listed in Table 5. The InP/(InP + BghiP) ratio can be used to identify the traffic sources. This value, ranging over , means that the PAHs content comes from diesel engine emission. 37 This ratio was determined in this work, and it was found to be in the range of Therefore, the PAHs found in Beijing should be partly due to diesel engine emission. The BaP/BghiP ratio was also utilized for this evaluation. The BaP/BghiP ratio, ranging over , indicated that traffic emission was responsible for the PAHs source. 38 Another way to identify the source of PAHs is the use of Ph/(Ph + An) ratio. By the definition, a value of this ratio over 0.70 indicates that lubricant oils and fossil fuel (including coal) combustions are the main sources of PAHs. 39 The BaP/(BaP + Chr) ratio was also considered in the present work. Khalili et al. 40 reported that this diagnostic ratio at values of 0.49 and 0.73 could be related to diesel and gasoline combustion, respectively. According to the definitions of the diagnostic ratios chosen by this work and to the data presented in Table 2, the PAHs content found in Beijing during the period of December 2004 to August relatively came from traffic exhaustion and domestic coal-burning heaters. Conclusions The total particle-associated PAHs concentrations in the urban air of Beijing are found to be ng/m 3. The PAHs concentration in the winter is higher than in the spring and the summer. A comparison using diagnostic ratios implies that the traffic exhaust, especially from vehicle with diesel engines, and domestic coal-burning heaters make a prominent contribution to the PAHs concentration in Beijing. More efforts should be made to control the serious air pollution in Beijing.

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