air6 by department of environmental quality promotion thailand

‚§√ß°“√»÷°…“¡≈¿“«–∑“ßÕ“°“»Õ—π‡π◊ËÕß¡“®“° “√‚æ≈’‰´§≈‘° Õ–‚√¡“µ‘°‰Œ‚¥√§“√å∫Õπ (PAH) „π∫√√¬“°“»‡¢µ°√ÿß‡∑æ¡À“π§√ 1. °“√®”·π°·≈–ª√‘¡“≥«‘‡§√“–Àå Airborne Polycyclic Aromatic Hydrocarbon (PAH) In Bangkok Urban Air I. Characterization and Quantification Hathairatana Garivait*, Wanna Laowagul* Phaka Sukasem*, Sunthorn Ngod-Ngam* Chongrak Polprasert**, Lars Baetz Reutergardh**

High Performance Liquid Chromatograph

∫∑§—¥¬àÕ

Incinerator

æƒµ‘ ° √√¡¢Õß “√‚æ≈’ ‰ ´§≈‘ ° Õ–‚√¡“µ‘ ° ‰Œ‚¥√§“√å∫Õπ (PAH) „π∫√√¬“°“»¢÷Èπ°—∫§ÿ≥ ¡∫—µ‘ ∑“ß¥â“πøî ‘° å·≈–‡§¡’¢Õß “√¥—ß°≈à“« ¥—ßπ—Èπ°“√ °√–®“¬µ—«·≈–°“√‡°‘¥ªØ‘°‘√‘¬“¢Õß “√ PAH „π ∫√√¬“°“»„π‡¢µ√âÕπ®÷ßπà“®–·µ°µà“ß®“°∑’Ë‡°‘¥¢÷Èπ „π∫√√¬“°“»‡¢µÀπ“« ·µàÕ¬à“ß‰√°Áµ“¡°“√»÷°…“ æƒµ‘°√√¡¢Õß “√ PAH „π∫√√¬“°“»‡¢µ√âÕπ¬—ß¡’ Õ¬ŸàπâÕ¬¡“°„πªí®®ÿ∫—π °“√»÷°…“§√—Èßπ’È ‰¥â∑”°“√ ”√«®≈—°…≥– ‡©æ“–¢Õß°“√°√–®“¬µ—«¢Õß “√ PAH „π∫√√¬“°“» ‡¢µ‡¡◊ Õ ß¢Õß°√ÿ ß ‡∑æ¡À“π§√ ‚¥¬§”π÷ ß ∂÷ ß °“√ °√–®“¬µ— « ¢Õß “√ PAH „π√Ÿ ª ¢Õß°ä “ ´·≈–„π

*»Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡ ‡∑§‚π∏“π’ µ.§≈ÕßÀâ“ Õ.§≈ÕßÀ≈«ß ®.ª∑ÿ¡∏“π’ 12120 ‚∑√. 0-2577-1136 ‚∑√ “√. 0-2577-1138 Environmental Research and Training Center, Department of Environmental Quality Promotion. Technopolis. Klong 5 Klong Luang, Pathumthani 12120 e-mail: hathairat@myrealbox.com **Asian Institute of Technology, Pathumthani, Thailand

√Ÿª¢ÕßΩÿÉπ≈–ÕÕß µ≈Õ¥®π°“√°√–®“¬µ—«„π√Ÿª¢Õß ΩÿÉπ≈–ÕÕß·∫∫·¬°¢π“¥ °“√‡°Á∫µ—«Õ¬à“ß∑”‚¥¬°“√ „™â ‡ §√◊Ë Õ ß‡°Á ∫ µ— « Õ¬à “ ßΩÿÉ π ≈–ÕÕß·∫∫·¬°¢π“¥ (Andersen çlow volumeé Sampler) µàÕ‡¢â“°—∫ À≈Õ¥‡°Á∫°ä“´ ∑’Ë∫√√®ÿ¥â«¬ XAD-2 “√ PAH 9 ™π‘¥ ∑’Ë∑”°“√»÷°…“‡ªìπ “√∑’Ë¡’§ÿ≥ ¡∫—µ‘‡ªìπ “√ °àÕ¡–‡√Áß·≈–‡ªìπ “√√à«¡°àÕ¡–‡√Áß ‰¥â·°à Pyrene (PYR), Benz(a) Anthraecene (BaA), Benzo(e) Pyrene (BeP), Dibenz(a,c)Anthracene (DBacA), Benzo(k)Fluoranthene (BkF), Benzo(a) Pyrcne (BaP), Dibenz(a,h) Anthracene (DBahA), Benzo(ghi) Perylene (BghiP) ·≈– Trimethylcholanthrene (3MC) ‚¥¬„™â°“√ °—¥·∫∫Õ—≈µ√â“ ‚´π‘ ° ·≈–„™â ‡ ∑§π‘ § High Pressure Liquid Chromatography (HPLC) „π°“√®”·π° “√∑—Èß 9 ™π‘¥ ·≈–°“√»÷°…“æ∫«à“‡∑§π‘§„π°“√‡°Á∫µ—«Õ¬à“ß∑’Ë ‰¥â Õ Õ°·∫∫¢÷È π „π°“√»÷ ° …“§√—È ß π’È ‡ À¡“– ¡„π°“√ ”√«® “√ PAH ∑’Ë ¡’ πÈ” Àπ— ° ‚¡‡≈°ÿ ≈ µ—È ß ·µà 202 ¢÷Èπ‰ª „π∫√√¬“°“»‡¢µ√âÕπ ‡π◊ËÕß®“°‰¡à¡’ “√ PAH „¥Ê „π 9 ™π‘¥ π’Èª√“°Ø„π™—Èπ∑’Ë 2 ¢Õßµ—«¥Ÿ¥´—∫ °ä“´ (XAD-2) ∑’Ë∫√√®ÿ„πÀ≈Õ¥‡°Á∫°ä“´ ∂÷ß·¡â «à “ Õÿ≥À¿Ÿ¡‘„π∫√√¬“°“»®– Ÿß∂÷ß 35 Õß»“‡´≈‡´’¬

ABSTRACT The behavior of airborne PAH is related to their physical and chemical properties. Thus, in a tropical urban environment, they are expected to have phase distributions and reactivities which are quite different from those established for temperate areas. Nevertheless, such studies are still scarce in the tropics. In this study, the characteristics of PAH in Bangkok urban air were investigated with respect to gas-particle partitioning and dependency on particle size. A sampling system which consisted of an 8 stage size fractionating cascade impactor (Andersen çlow volumeé Sampler) and a downstream XAD-2 adsorbent tube was used for sample collection. Nine PAH, classified as carcinogenic and co-carcinogenic compounds - Pyrene (PYR), Benz (a) Anthracene (BaA), Benzo (e) Pyrene (BeP), Dibenz(a,c)Anthracene (DBacA), §-46

Benzo(k)Fluoranthene (BkF), Benzo(a) Pyrene (BaP), Dibenz(a,h)Anthracene (DBahA), Benzo(ghi)Perylene (BghiP) and Trimethylcholanthrene (3MC) - were quantified by ultrasonic extraction and HPLC with fluorescence detection. The quantitative and qualitative compositions of these nine PAH samples are described. It was concluded that1 the sampling system designed in this study is suitable for the investigation of airborne PAH (with molecular weights of 202 and above) in the tropical climate since even at sampling temperatures of ~ 35 ÌC, none of the listed PAH was traceable in the second layer of the XAD-2 adsorbent tube.

1. Introduction Polycyclic Aromatic Hydrocarbons (PAH) in the environment are almost exclusively generated from combustion sources. They were one of the first atmospheric pollutants to be identified as being carcinogenic and mutagenic. 1-3 Due to their moderate volatilities, PAH are found in the atmosphere in two forms; adsorbed on suspended particles and in the gas phase. 4-6 The association of PAH with the respirable fraction of airborne particulate matter and their corresponding gas phase are of particular importance in terms of their human health effects. 7-9 Furthermore, ambient urban air levels of PAH are of concern because they are produced from the combustion of fossil fuels. In deed, they are present in emissions from many stationary and mobile combustion sources, including those from refuse incineration10 and combustion of gasoline and diesel by vehicles.11-13 In this study, an investigation on airborne PAH was carried out in the Bangkok area where air pollution is of significant concern. Being the capital of Thailand, Bangkok is the largest city with a population of 8 millions and a population density of 4,615 »Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡

inhabitants/km2. Given current growth patterns, the city will be a megacity in the year 2000. The city lies in the monsoon zone in which seasonal monsoon winds and sea breezes prevail. The city is now facing serious air pollution problems, since it has been the center of rapid development in the country during the past 5 decade. Particulate matter pollution for particles equal to or less than 10 µm in diameter (PM10) often exceeds the U.S. 24 hours standard of 150 mg/m3 for days and weeks at a time. The major origins of particulate matter pollution could be attributed to construction activities and motor vehicle traffic.14 At present, progress in the control of atmospheric particulate matter in Thailand is evaluated by calculating the total weight of material collected by using a standard high volume technique. This technique has been applied to both total suspended particulate matter (since 1981) and PM10 (since 1995). The PM10 levels in Bangkok urban areas generally exceeded the Thai ambient air quality standard value of 120 mg/m3 over a 24 hours period. This severe situation may reflect the fact that the air pollution control techniques and/or technologies we have been using in this area may not be very effective for the particles in the respirable size range (< 5 µm). Various issues have recently been investigated to mitigate the air pollution in Bangkok, e.g. Air Quality Management Planning (1991); A Review of Current Air Quality Standard (1993); Characterization of ambient Suspended Particulate Matter (SPM) in the Bangkok Metropolitan Region, BMR (1996). These studies only emphasized the quantity and elemental composition of SPM. Those focus on the carcinogenic substances such as PAH in airborne particulate matter are still scarce in this country, even though statistics on cancer in Thailand from 1988 to 1991 have shown that lung cancer is »Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡

the most common form of cancer in both sexes in areas where the air pollution levels are considered dangerous.15 On the other hand, many studies addressing carcinogenic substances in airborne particulate matter were performed worldwide over 20 years ago. However, most of them were conducted in temperate environments. Although the concentrations of PAH in urban environments have been extensively studied, there are very few reports from tropical areas and there is a notable paucity of data from the Association of Southeast Asian Nations (ASEAN) region. The levels and distributions of airborne PAH in a tropical environment are expected to be different from those obtained in the temperate ones due to differences in type and scale of emission sources as well as air temperature In Thailand, the first study of this type was done by Matsushita et al. (1987).16 Carcinogenic PAHs in airborne particulate in Bangkok, Chiang Mai and Tokyo were compared. At that time, only total suspended particulate matter was considered. The influences of the particle size and of the corresponding gas phase on the PAH composition were not documented. The objective of this study is to implement an appropriate sampling and analytical technique to investigate the amount of airborne PAH with respect to their particle size dependency and phase distribution in Bangkok. This aims to provide an understanding of the environmental fate and the extent of human exposure to these substances in a tropical environment.

2. Methods and Materials 2.1 Sampling Locations To measure PAH and to characterize PAH composition with respect to their gas-particle partitioning and size dependency in the Bangkok urban area, an urban residential site, the Office of Environmental §-47

Policy and Planning (OEPP), was selected from the National Air Quality Monitoring Network in Bangkok. It is located in the urban center and is surrounded by commercial buildings, government offices, houses, roads and expressways. Moreover, there are few industries within a 10 km radius of the sampling site. The sampler was placed about 20 meters from the ground on the top of a 7-story building.

2.2 Sampling System To investigate the gas-particle distribution and particle size dependency of PAH, a combination of an Andersen low volume cascade impactor (SIBATA model AN-200) followed by a glass tube containing XAD-2 polymer beads was used (Figure 1). The selection was made after considering the advantage of impactor sampling which provides minimal contact of collected particulate matter with the air stream so that

the particle blow-off effect can be kept to a minimum. Furthermore, cascade impactor sample provides particles over the inhalable size range. T60A20 Teflon-coated glass fiber filters were used to collect particles on each of the impactor stages as well as particles that were too small to be collected by the impactor. T60A20 appears to have superior filtering qualities because of its reduced surface activity.17 This may contribute to a reduced degradation of collected PAH during sampling and storage. XAD-2 (Styrenedivinylbenzene polymer beads) was used to adsorb gas-phase constituents. XAD-2 adsorbent has several advantages in terms of collection efficiency, good recovery of adsorbed compounds and minimal degradation during storage.18 In order to insure the proper aerodynamic cut-off diameter for 50% collection efficiency, it is necessary to operate the sampling system at a flow rate of 28.3 L/min. Under these conditions, the

Figure 1 Sampling system used in this study.

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»Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡

equivalent aerodynamic cut-off diameters at 50% collection efficiency for each stage of the impactor are given in Table 1. The XAD-2 adsorbent tube was designed in this study by referring to the level of pressure drop across the sampler in order to maintain constant flow rate during the sampling period. The design of the XAD-2 adsorbent tube is illustrated in Figure 1. The sampling system was calibrated according to the procedure described in the SIBATA model AN-200 Corporationûs manual.

2.3 Materials Teflon coated glass fiber filters (T60A20) with a diameter of 80 mm were purchased from the Pallflex Corp. SIBATA, Japan. The purity of the filters was checked before use by carrying out the same extraction and analysis procedure as that for the samples. The blank values of the target compounds in the extracts from these filters were generally below their detection limits, and therefore, no pre-treatment of the filters was necessary. The filters were conditioned at constant relative humidity (50 ± 2%) and temperature (24 ± 2 ÌC) in a dark desiccator for 24 hours prior to weighing. They were then wrapped with clean Aluminum foil and kept in a capped plastic bag until sampling.

XAD-2 was purchased from the ORGANO Company, Japan. Each XAD-2 was cleaned by first soaking in methanol followed by two Soxhlet extractions with a mixture of dichloromethane : acetonitrile (1:1, v/v) for 16 hours. It was then heated at 70 ÌC to dryness in a clean oven for about 30 min. The cleaned XAD-2 was placed in a clean polyethylene bottle with a screw cap. XAD-2 blanks were evaluated by the same analysis used for target gaseous samples. The cleaning procedure of XAD-2 was repeated until low blank values were obtained (each selected PAH < 10ng/12g XAD-2). The packing of the XAD-2 adsorbent tube was done in the laboratory. The two ends of the tube were closed with Teflon tape and polyethylene caps. The tube was, then, wrapped with Aluminum foil to protect it from light and kept in a capped plastic bag until sampling. All solvents were chromatographic grade (MERCK, Germany). Individual PAH standard reagents were purchased from Wako Pure Chemical Industries (Osaka, Japan) and Standard Reference Material (Urban Dust, SRM 1649c) was obtained from the National Institute of Standards and Technology (NIST), USA. The cleaning procedure for glassware was done according to the guideline of U.S.EPA method TO-13.19

Table 1 SIBATA, AN-200 low volume cascade impactor characteristics. Stage number

Equivalent aerodynamic cut-off diameters at 50% efficiency (µm.)

0 1 2 3 4 5 6 7 backup

> 11 7.0 - 11 4.7 - 7.0 3.3 - 4.7 2.1 - 3.3 1.1 - 2.1 0.65 - 1.1 0.43 - 0.65 < 0.43

»Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡

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2.4 Sample Collection and Analysis To avoid wet removal of airborne PAH , the study was done during the dry season when SPM pollution in Bangkok is the most serious. Sample collection was performed by drawing air at flow rate of 28.3 L/min. through the sampling unit. The particulate phase was defined as that trapped on the filters for all eight stages of the impactor and the backup filter in the particle size separation unit. The corresponding gas phase was defined as that associated with the two layers of XAD-2 packed in the adsorbent tube. PAH were sampled for 24 hours during 23-29 May 1996, resulting in 7 sets of samples. The exposed filters were folded in half and wrapped separately in Aluminum foil; then the set was kept together in a capped plastic bag, while the exposed XAD-2 adsorbent tube was capped and put into a capped plastic bag to reduce contamination. After collection, the samples were transferred back to the laboratory where the filters were dried in a dark desiccator for 24 hours and weighed 3 times on a 5 decimal place gram analytical balance. Weight differences were used to determine the particulate matter concentration in each particle size range. All samples were stored at -85 ÌC in the dark until extraction. 20

2.5 Chemical Analysis 2.5.1 Particle-bound PAH A very sensitive analytical method (Matsushita et al., 1994)21 was referred to determine particulate-PAH concentrations in this study. This method was developed to survey indoor PAH pollution. It was appropriate for this study because sample collection was performed with an Andersen low volume air sampler for only 24 hours, hence requiring high sensitivity. The description of analytical procedure is outlined as follows: §-50

Two or four circular samples, each of 25 mm diameter, were punched out from each stage of the Andersen sampler and cut into small pieces with ceramic scissors. All pieces were put into a screw cap centrifuge tube (20 mL) with a Teflon liner. 15 mL of dichloromethane was added to the tube. The tube was sealed and placed in an ultrasonic bath (38 Hz, 250 W) and sonicated twice for 20 min at 10 ÌC. The tube was then centrifuged at 3000 rpm for 10 min. 10 ml of supernatant was transferred to a small test tube, and 30 µL of DMSO (dimethylsulfoxide) was added to retain PAH. The test tube was then set in a dry thermostat unit (Taitec, Model DTU-1B) at about 30 ÌC and the dichloromethane was evaporated under a gentle nitrogen stream. The residue in the test tube was dissolved with 970 mL of acetonitrile. Finally, the extracted samples were filtered prior to separation analysis using a CAMEO II, filter assembly with a 0.22 µm pore Nylon filter. 2.5.2 Gas phase PAH Each exposed XAD-2 adsorbent (i.e. 12 g and 5 g) was extracted separately twice with a 100ml mixture of acetonitrile and dichloromethane 1:1 (v/v) in an ultrasonic bath for 20 min at 10 ÌC. The crude extracts were treated identically to the aerosol extracts.

2.6 Determination of PAH Separation analysis was performed on a Shimadzu LC9A High Performance Liquid Chromatograph (HPLC) with fluorescence detection. Excitation and emission wavelengths were 295 nm and 405 nm, respectively. A wide bore Octadecyl column (C18, 5 mm., Wakosil) 4.6 x 250 mm and an identical pre-column of 50 mm were used. The mobile phase flow was 1mL/min and the gradient conditions were: 50% acetonitrile in water (5 min) followed by, 50% to 85% (20 min, linear), 85% to 100% (20 min, linear), 100% (20 min). The temperature of the columns

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was maintained at 40 Ì C and a 50 mL injection volume was used. The two eluents, acetonitrile and water, were filtered through 0.22 µm filters before use. The nine PAH, classified as carcinogenic and co-carcinogenic compounds - Pyrene (PYR), Benz(a) Anthracene (BaA), Benzo(e)Pyrene (BeP), Dibenz(a,c)Anthracene (DBacA), Benzo(k) Fluoranthene (BkF), Benzo(a)Pyrene (BaP), Dibenz(a,h)Anthracene (DBahA), Benzo(ghi) Perylene (BghiP) and Trimethylcholanthrene (3MC) - were identified and their concentrations determined by comparison with a mixture of authentic standards.

3. Results and Discussion 3.1 Reliability of PAH Analysis In the study, nine PAH compounds were selected as indicators of atmospheric carcinogenicity and/or mutagenicity. Before the sampling program, the recovery of PAH on XAD2 and on the filters was determined. This involved spiking six separate XAD-2 adsorbent (12 grams) and six filters with a working standard containing all the PAH compounds. Generally, reasonable recovery was obtained for the selected PAHs as shown in Table 2. The minimum detectable concentration of

PAH in ng/m3 represented a value equivalent to a 40 m3 air sample and 50 µL HPLC injection, the normal operating conditions in this study. Table 3 indicates the detection limits of the PAH ranging from 0.01 to 0.04 ng/ m3. The relative standard deviations were l ess than 15%. The minimum detectable concentrations in the vapor phase were slightly higher than those in the particulate phase. This is probably due to the blank quality of the XAD-2: the extract from the blank XAD-2 presented high background peaks of different PAH of interest, especially BeP. Each PAH compound was quantified against a series of calibration standards made up from the stock solution. In order to verify the calibration, a confirmation working standard was run each time after 10 sample injections. For quality assurance, Standard Reference Material (SRM) 1649c Urban Dust was run for the selected PAH. The resulting values were in good agreement with certified values given for this material (see Table 4). Typical chromatograms of particulate and gaseous phase PAH are shown in Figure 2. The result showed that the target PAH in particulate and gas phase samples could be analyzed without any major interference from other coexisting PAH.

Table 2 Recovery of the selected PAH from the XAD-2 and the filter substrate PAH PYR BaA BeP DBacA BkF BaP DBahA BghiP 3MC

% recovery (RSD)*, average of 6 runs. XAD-2 Filters 75.3 (4.8) 89.4 (4.3) 78.5 (6.3) 83.3 (13) 91.7 (4.3) 89.6 (5.9) 72.8 (18) 93.6 (8.0) 92.7 (6.7)

95.1 (2.3) 93.4 (4.1) 89.3 (8.0) 76.8 (6.7) 90.5 (5.6) 90.6 (5.0) 85.3 (9.1) 88.5 (7.0) 89.5 (6.3)

* RSD = Relative Standard Deviation. »Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡

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Table 3 Minimum detectable concentration of the PAH in the particulate and vapor phases. Minimum detectable conc. of PAH, ng/m3 Particulate phase Vapor phase 0.04 0.05 0.01 0.03 0.02 0.05 0.01 0.03 0.02 0.03 0.02 0.05 0.02 0.03 0.03 0.03 0.03 0.03

PAH PYR BaA BeP DBacA BkF BaP DBahA BghiP 3MC

Table 4 Mean concentrations of PAH analyzed in Reference Urban Dust (SRM 1649c), average in 7 runs. PAH PYR BaA BeP DbacA BkF BaP DbahA BghiP 3MC

mg/g (SD) 7.08 (0.12) 2.60 (0.16) 4.30 (0.30) 0.32 (0.04) 2.00 (0.10) 2.50 (0.10) 0.65 (0.02) 3.81 (0.18) nd.

Certified Value 6.3 ± 0.4 2.8 ± 0.3 2.0 ± 0.1 2.6 ± 0.4 3.9 ± 0.8 -

SD = Standard Deviation, nd = not detected Table 5 Average PAH concentrations (ng/m3) of air samples collected at OEPP, number of observation; n = 7 PAH PYR BaA BeP DBacA BkF BaP DBahA BghiP 3MC

0 0.040 0.038 0.022 nd nd nd nd nd nd

1 0.143 0.047 0.042 nd nd nd nd nd nd

Andersen stage number 2 3 4 5 0.146 0.070 0.062 0.051 0.054 0.041 0.037 0.032 0.083 0.06 0.06 0.104 nd nd nd nd nd nd nd 0.024 nd nd nd 0.034 nd nd nd nd nd 0.030 0.042 0.111 nd nd nd nd

6 0.175 0.050 0.141 0.016b 0.059 0.083 0.026a 0.28 nd

7 Backup 0.221 0.352 0.070 0.136 0.151 0.357 nd 0.044b 0.067 0.248 0.137 0.413 nd 0.039d 0.363 1.281 nd 0.05c

Filter (P-PAH) 1.30 0.50 1.02 0.06 0.40 0.67 0.07 2.11 0.05

XAD-2* (G-PAH) 12.70 0.16 0.27 nd nd nd nd nd nd

Total** conc. 14.00 0.65 1.29 0.06 0.43 0.67 0.67 2.11 0.05

* **

Experiments with two XAD-2 layers inseries; none of the listed PAHs were traceable in the second layer. Total conc. = Particulate phase + Gaseous phase PAH. a,b,c,d Indicate the average value of n =1, n = 2, n = 3, n = 5, respecively. n = number of observations. P-PAH = particle bound PAH. G-PAH = gaseous PAH.

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»Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡

Figure 2 Typical chromatograms of airborne PAHs extract and PAH standard solution.

Figure 3 Relative proportion of airborne PAHs in gas and particulate phases at OEPP sampling site.

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3.2 PAH Concentrations Field sampling was conducted at the OEPP sampling site, a Bangkok urbanresidential area, during 7 days of the dry season (May 1996). The ambient temperatures ranged from 27 to 30 ÌC and relative humidity ranged from 73 to 85%. At this site, the prevailing wind direction during sampling was S/SE or S/SW and wind speeds ranging from 1.7 to 2.3 m/s. The concentration data of PAH in the different particle sizes and their distribution in vapor phase are shown in Table 5 and Figure 3. It is obvious that, PYR, BaA, BeP, BkF, BaP and BghiP were predominant in this area. Results showed that the fraction in the gas phase increased with increasing volatility. Pyrene was almost entirely in the gas phase, BaA and BeP were about 25% and 21% in the gas phase, respectively. All the other compounds had negligible gas-phase concentrations. Particulate-PAH were found mostly on particles less than 2.1 µ m in size. These results were consistent with other studies22-24 with the exception of BaA and BeP. Their relative proportion in the gas phase (25% and 21%, respectively) seemed to be lower than in other studies. This may due to the fact that PAH of four rings or less exist mainly in the gas phase under typical ambient conditions, enabling them to undergo atmospheric reactions with any one of several reactive substances such as hydroxyl radicals, ozone and nitrate radicals, which are present at low concentrations in the troposphere.25-27 Besides, sunlight intensity has the strongest influence on PAH decay.28 These reactions would thus result in relatively short atmospheric lifetimes for the gas-phase PAH. The strong sunlight in the tropical climate, poor air quality in Bangkok, and the significant time scales required to re-establish equilibrium after gas-phase photolysis and reaction with the pollutants 29 may thus explain the lower §-54

proportion of BaA and BeP in gas phase. It should be noted that in the temperate environment, the amount and range of PAH in the urban areas exhibit seasonal fluctuations. In most cases, higher levels are apparent in winter compared to summer. The reasons are not only due to changes in the contributions of the possible sources like residential heating and automobiles to the PAH levels, but they are also the results of a higher atmospheric reactivity of PAH during the summer months.26,28,30 The total concentrations of the individual PAH obtained in an urban residential area (Table 5) was generally consistent with summertime results in temperate environments reported by other authors using similar sampling techniques (Filter with adsorbent backup)22,24,31 when domestic heating was not in use, although higher atmospheric reactivity would be expected in the Bangkok urban air. Although 16 PAH species have recently been identified as hazardous air pollutants in the Title III of the U.S. Clean Air Act Amendments of 1990, there are still no air quality standards set for PAH. Only BaP, the most carcinogenic of the PAH, has been widely studied. According to WHO (World Health Organization) Guideline 1987, the estimated lung cancer risk, connected with exposure to 1 ng/m 3 of BaP for a lifetime, would be 9 x 10-5. The level of BaP obtained in this study, 0.67 ng/m3, was still within the WHO Guideline. However, more investigations are needed in terms of concentration and distribution of airborne PAH in this area.

4. Conclusion The results obtained in this study have shown that the experimental setting adapted from the literature is appropriate for investigating the characteristics and quantity of PAH content in Bangkok urban air. It is worth noting that the concept of an Andersen cascade low volume impactor in combination »Ÿπ¬å«‘®—¬·≈–Ωñ°Õ∫√¡¥â“π ‘Ëß·«¥≈âÕ¡ °√¡ àß‡ √‘¡§ÿ≥¿“æ ‘Ëß·«¥≈âÕ¡

with XAD-2 adsorbent tube represent a suitable alternative of obtaining results that takes into account the phase distribution and the particle size dependency of airborne PAH. The collection of the gas phase PAH by the XAD-2 adsorbent tube, specially designed in this study, was found to be a well-adapted tool for sampling in tropical climates where sunlight and temperature conditions are expected to strongly influence the gas-particle partitioning of certain PAH. In deed, we noted in this study that even at the sampling temperatures of ~ 35 ÌC during daytime, none of the listed PAH (with molecular weights of 202 and above) was detected in the backup layer of the XAD-2 adsorbent tube.

10.

5. Acknowledgements

11.

We gratefully acknowledge Environmental Research and Training Center, Thailand for the support of this study. The very helpful advices of Professor H. Matsushita and Dr. T. Amagai, University of Shizuoka, Japan for the establishment of the analytical method are greatly appreciated. We are extremely grateful to Professor R.M. Kamens and Dr. M. R. Strommen, University of North Carolina at Chapel Hill USA, for their very helpful comments. We also deeply appreciate Pollution Control Department, Thailand for the support of air quality monitoring data in Bangkok.

5. 6. 7. 8. 9.

12. 13.

14.

15.

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