**1. Introduction**

28 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

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(Cambridge Univ., UK, New York), Ch. 2, pp. 130–234 Isaev, A.A. (2001). *Ecological Climatology* (Naucka. Mir, Moscow, 2001)

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No. 1, pp. 34 – 46, ISSN 1068 – 3739

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IPCC, Climate Change (2001). Working Group I, *Contribution to the Intergovernmental Panel on Climate Change. 3rd Assessment Report Climate Change 2001: the PhysicalSciense Basis* 

IPCC, Climate Change (2007). Working Group I, *Contribution to the Intergovernmental Panel on ClimateChange. 4th Assessment Report of Climate Change: ThePhysical Science Basis* 

Jevrejeva, S., Moore, J., Grinsted, A. (2003). Influence of the Arctic Oscillation and El Nino-Southern Oscillation (ENSO) on ice conditions in the Baltic Sea: The wavelet approach,

Luts'ko, L.; Makhotkina, E.; Klevantsova, V. (2001). The Development of Actinometric Observations, *Current Studies of the Main Geophysical Observatory: A Jubilee Collection* ,

Makhotkina, E.; Plakhina, I.; Lukin, A. (2005). Some Feature of Atmospheric Turbidity Change over the Russian Territory in the Last Quarter of the 20th Century . *Russian* 

Makhotkina, E.; Lukin, A. Plakhina, I. ( 2007). Monitoring of Integral Atmosphere Transparency. *Proc. of the All-Russ. Conf. on Development of Monitoring System of* 

Makhotkina, E.; Plakhina, I.; Lukin, A. (2010). Changes in Integral and Aerosol Atmospheric Turbidity in Trans-Baikal and Central Siberia. *Russian Meteorology and Hydrology, Vol.35,* 

Ohmura, A. (2006). Observed Long-term Variations of Solar Irradiance at the Earth Surface*.* 

Plakhina, I.; Makhotkina, E.; Pankratova, N. (2007). Variations of Aerosol Optical Thickness of the Atmosphere in Russia in 1976-2003. *Russian Meteorology and Hydrology,* Vol. 32,

Plakhina, I.; Pankratova, N., Makhotkina, E. (2009). Variations in the Aerosol Optical Depth from the Data Obtained at the Russian Actinometric Network in 1976-2006. *Izvestiya,* 

Sitnov, S. (2010). The Results of Satellite Monitoring of the Content of Trace Gases in the Atmospheric and Optical Characteristics of Aerosol over the European Territory of Russia in April–September 2010, in AllRussia Meeting on the Problem of the State of the Air Basin in Moscow and European Part of Russia under the Extreme Weather

Conditions in Summer 2010 pp. 26–27, http://www.ifaran.ru/messaging/forum/

*Atmospheric and Oceanic Physics*, Vol. 45, No. 4, pp. 456 – 466, ISSN 0001 – 4338 Plakhina, I.; Pankratova, N., Makhotkina, E. (2011). Spatial Variations in the Air Turbidity Factor above the European part of Russia under Conditions of Abnormal Summer of 2010. *Izvestiya, Atmospheric and Oceanic Physics*, Vol. 47, No. 6, pp. 708 – 713, ISSN 0001 – Polycyclic aromatic hydrocarbons (PAHs) have been drawing attention as a major hazardous air pollutant due to their potential carcinogenicity and mutagenicity [1-2]. Polycyclic aromatic hydrocarbons are formed during the incomplete combustion of oil, coal, gas, wood and other organic substances. PAHs are initially generated in the gas phase, and they are adsorbed on pre-existing particles undergoing condensation during further cooling of the emission. Thus, most atmospheric PAHs exist in the particulate phase, while some higher volatility PAHs or low molecular weight PAHs remain partly in the gas phase (e.g., [3]). There are basically five major emission source components: domestic, mobile, industrial, agricultural and natural. The relative importance of these sources changes depending on the place or regulatory views; however, in the urban environment with heavy traffic, mobile source, that is vehicle exhaust is the main contributor to the atmospheric PAHs (e.g., [3-6]). Thus, health risk of the dense urban population by the exposure to those PAHs has been of concern both in developed and developing countries.

Currently, PM10 or finer particles are major air pollutants in many urban areas. In the atmosphere, PAHs are partitioned between gaseous and particulate phases as explained earlier. Especially, PAHs of higher molecular weight species, which are often of higher carcinogenic potential, are mostly associated with fine particulate matter (e.g., [2, 7]). However, atmospheric behavior of particulate matter is known to be highly complicated in terms of its chemical compositions, size distributions, physical behavior, reactions, and so on. Accordingly, atmospheric behavior of PAHs associated with particulate matter is subjected to uncertainties and still poorly explained, including their temporal and spatial variations.

© 2012 Hoshiko et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Hoshiko et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Thailand's capital city, Bangkok was selected as the field of this study, where traffic air pollution and its health effects have long been a serious problem due to the heavy traffic and the chronic state of traffic congestion. It was reported that about 88% of PAH emission is attributed to motor vehicles, and a minor contributions are from biomass burning and oil combustion [6]. In Bangkok, road traffic is the main transport. Diesel buses have been the primary public transport, and ownership of passenger cars- both gasoline and diesel- and motorcycles has been increasing. The mass rapid transit network is still insufficient to meet the dramatically increased travel demand, which arose concurrently with the rapid economic development and rise in population in the last several decades. Thus, road traffic is heavily congested. At present, overall air quality in Bangkok has been significantly improved owing to several effective policies taken in the last decade, and the initiation and ongoing extension of railways and reinforcement of vehicle emission controls are quite promising for the further improvement. This is recognized as a successful case of urban air quality improvement in Southeast Asia, where many cities are still suffering from serious air pollution. In spite of the improvement, the present roadside PM10 levels in Bangkok have still been constantly exceeding the standard values; 24 hour standard 120 μg/m3 and annual standard 50μg/m3 [8]. Given the situation, carcinogenic PAHs associated with particulate matter are suspected to contribute to an increased health risk for the people living in the city.

Temporal Variation of Particle Size Distribution of Polycyclic Aromatic Hydrocarbons at Different Roadside Air Environments in Bangkok, Thailand 31

cool (November - February). In terms of their characteristics, the hot season is hot and dry, the wet season is hot and wet, and the cool season is cool and dry. Field measurements were conducted in March and April, 2006, in the hot season. Concentrations of particulate phase PAHs were measured on the roadside in Bangkok. Diurnal variations of PAH concentrations were investigated by comparing two roadside sites with different road configurations. The measurement sites were Rama6 (R6) and Chockchai4 (CC). The R6 site is located in the area of government offices in the Bangkok city center, where one of the main roads, R6, carries heavy traffic. The R6 road is covered by an elevated highway (Figure 1a), and this configuration, together with large roadside buildings, is likely to cause a stagnant air mass within the road space. By contrast, the CC site has an ordinary open-space configuration along the Ladphrao road, with low-rise small buildings (Figure 1b). The measurement points were approximately three meters distance from the roads at both sites, 1.5 meters height from the ground at R6 (Figure 2a) and three meters height at CC in a Pollution Control Department's (PCD) air monitoring station, where the rooftop space of the

station was provided to install measurement equipment for this study (Figure 2b).

Particle mass was collected using a 10-stage Micro Orifice Uniform Deposit Impactor (MOUDI, Model 110, MSP Corporation, U.S.A.) [18] (Figure 3). The principle operation of the MOUDI is the same as any inertial cascade impactor with multiple nozzles. At each stage, jets of particle-laden air impinge upon an impaction plate, and particles larger than the cut-size of that stage cross the air stream lines and are collected upon the impaction plate. The smaller particles with less inertia do not cross the streamline and proceed to the next stage where the nozzles are smaller and where the air velocity through the nozzle is higher, and there, the finer particles are collected. This continues through the cascade impactor until the smallest particles are collected by the after-filter [19]. Figure 4 shows a schematic diagram of one stage

(a) (b)

of the MOUDI, showing its relation to the above and below stages [19].

**Figure 1.** Figure 1. Study sites. a) Rama6; b) Chockchai4

**2.2. Air sampling** 

Previous studies on roadside measurements reported much higher levels of PAHs than those at ambient sites, which has been the case for Bangkok as well [6,9-13]. It is stressed that environmental monitoring of PAHs is needed in more comprehensive ways with higher resolutions of time and space, especially at roadside areas, which are possible hot spots of high levels of exposure. In PAH monitoring, temporal variations of concentrations are an important aspect, for example, seasonal and diurnal changes. As for seasonal variations, monitoring data in developed countries in the temperate regions, such as Western Europe and the USA, are relatively abundant, whereas in developing countries in the tropical regions including Thailand, data are limited. For diurnal variations, there have not been many cases reported because PAH concentrations are usually reported as daily average. However, some previous reports showed remarkable diurnal changes in PAH concentrations, with morning and evening peaks in parallel with traffic rush hours (e.g., [5,12,14-17]). If we further look into the behavior of PAHs, information on diurnal variations of particle size-fractioned PAH concentrations become of interest, because particulate matter of different sizes is known to exert different levels of adverse health effects in the human body and finer particles penetrate into deeper parts of the human body and cause respiratory or cardiovascular disorders. However, studies concerning such information have been quite limited. Therefore, the specific objective of this study is to investigate diurnal variations of particle size distribution of PAHs by conducting field measurements.

## **2. Methodology**

## **2.1. Study sites and time**

Bangkok has a population of more than eight million people. Its climate is classified as tropical savanna with three seasons: hot (March – mid May), wet (mid-May - October) and cool (November - February). In terms of their characteristics, the hot season is hot and dry, the wet season is hot and wet, and the cool season is cool and dry. Field measurements were conducted in March and April, 2006, in the hot season. Concentrations of particulate phase PAHs were measured on the roadside in Bangkok. Diurnal variations of PAH concentrations were investigated by comparing two roadside sites with different road configurations. The measurement sites were Rama6 (R6) and Chockchai4 (CC). The R6 site is located in the area of government offices in the Bangkok city center, where one of the main roads, R6, carries heavy traffic. The R6 road is covered by an elevated highway (Figure 1a), and this configuration, together with large roadside buildings, is likely to cause a stagnant air mass within the road space. By contrast, the CC site has an ordinary open-space configuration along the Ladphrao road, with low-rise small buildings (Figure 1b). The measurement points were approximately three meters distance from the roads at both sites, 1.5 meters height from the ground at R6 (Figure 2a) and three meters height at CC in a Pollution Control Department's (PCD) air monitoring station, where the rooftop space of the station was provided to install measurement equipment for this study (Figure 2b).

**Figure 1.** Figure 1. Study sites. a) Rama6; b) Chockchai4

## **2.2. Air sampling**

30 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

Thailand's capital city, Bangkok was selected as the field of this study, where traffic air pollution and its health effects have long been a serious problem due to the heavy traffic and the chronic state of traffic congestion. It was reported that about 88% of PAH emission is attributed to motor vehicles, and a minor contributions are from biomass burning and oil combustion [6]. In Bangkok, road traffic is the main transport. Diesel buses have been the primary public transport, and ownership of passenger cars- both gasoline and diesel- and motorcycles has been increasing. The mass rapid transit network is still insufficient to meet the dramatically increased travel demand, which arose concurrently with the rapid economic development and rise in population in the last several decades. Thus, road traffic is heavily congested. At present, overall air quality in Bangkok has been significantly improved owing to several effective policies taken in the last decade, and the initiation and ongoing extension of railways and reinforcement of vehicle emission controls are quite promising for the further improvement. This is recognized as a successful case of urban air quality improvement in Southeast Asia, where many cities are still suffering from serious air pollution. In spite of the improvement, the present roadside PM10 levels in Bangkok have still been constantly exceeding the standard values; 24 hour standard 120 μg/m3 and annual standard 50μg/m3 [8]. Given the situation, carcinogenic PAHs associated with particulate matter are suspected to contribute to an increased health risk for the people living in the city. Previous studies on roadside measurements reported much higher levels of PAHs than those at ambient sites, which has been the case for Bangkok as well [6,9-13]. It is stressed that environmental monitoring of PAHs is needed in more comprehensive ways with higher resolutions of time and space, especially at roadside areas, which are possible hot spots of high levels of exposure. In PAH monitoring, temporal variations of concentrations are an important aspect, for example, seasonal and diurnal changes. As for seasonal variations, monitoring data in developed countries in the temperate regions, such as Western Europe and the USA, are relatively abundant, whereas in developing countries in the tropical regions including Thailand, data are limited. For diurnal variations, there have not been many cases reported because PAH concentrations are usually reported as daily average. However, some previous reports showed remarkable diurnal changes in PAH concentrations, with morning and evening peaks in parallel with traffic rush hours (e.g., [5,12,14-17]). If we further look into the behavior of PAHs, information on diurnal variations of particle size-fractioned PAH concentrations become of interest, because particulate matter of different sizes is known to exert different levels of adverse health effects in the human body and finer particles penetrate into deeper parts of the human body and cause respiratory or cardiovascular disorders. However, studies concerning such information have been quite limited. Therefore, the specific objective of this study is to investigate diurnal

variations of particle size distribution of PAHs by conducting field measurements.

Bangkok has a population of more than eight million people. Its climate is classified as tropical savanna with three seasons: hot (March – mid May), wet (mid-May - October) and

**2. Methodology** 

**2.1. Study sites and time** 

Particle mass was collected using a 10-stage Micro Orifice Uniform Deposit Impactor (MOUDI, Model 110, MSP Corporation, U.S.A.) [18] (Figure 3). The principle operation of the MOUDI is the same as any inertial cascade impactor with multiple nozzles. At each stage, jets of particle-laden air impinge upon an impaction plate, and particles larger than the cut-size of that stage cross the air stream lines and are collected upon the impaction plate. The smaller particles with less inertia do not cross the streamline and proceed to the next stage where the nozzles are smaller and where the air velocity through the nozzle is higher, and there, the finer particles are collected. This continues through the cascade impactor until the smallest particles are collected by the after-filter [19]. Figure 4 shows a schematic diagram of one stage of the MOUDI, showing its relation to the above and below stages [19].

Temporal Variation of Particle Size Distribution of Polycyclic Aromatic Hydrocarbons at Different Roadside Air Environments in Bangkok, Thailand 33

> Vapor pressure (Pa at 25 ºC)

Solubility in water

(μg/L at 25 ºC)

**Figure 4.** Schematic diagram of a MOUDI stage showing its relation to the above and below stages [19]

No. of aromatic rings

Molecular weight

Phenanthrene Phe C14H10 178 3 1.6×10-2 1.3×103 Anthracene Ant C14H10 178 3 8.0×10-4 73 Fluoranthene Fluo C16H10 202 4 1.2×10-3 260 Pyrene Pyr C16H10 202 4 6.0×10-4 135 Benzo(a)anthracene BaA C18H12 228 4 2.8×10-5 5.6 Chrysene Chr C18H12 228 4 8.4×10-5 \* 2.0 Benzo(b)fluoranthene BbF C20H12 252 5 6.7×10-5 \* 0.80 Benzo(k)fluoranthene BkF C20H12 252 5 1.3×10-8 \* 0.76 Benzo(e)pyrene BeP C20H12 252 5 7.6×10-7 6.3 Benzo(a)pyrene BaP C20H12 252 5 7.4×10-7 3.8

cd)pyrene IP C22H12 276 6 1.3×10-8 \* 62 Dibenz(a,h)anthracene DahA C22H14 278 5 1.3×10-8 \* 1.0 Benzo(g,h,i)perylene BghiP C20H12 276 6 1.4×10-8 0.26

To monitor the temporal variations of total concentrations of particulate PAHs, photoelectric aerosol sensors (model PAS2000CE, EcoChem Analytics, Germany) [20] were used for realtime monitoring (Figure 5). Photoelectric aerosol sensors (PAS) work on the basis of photoelectric ionization of PAHs adsorbed onto particles [21]. The measurement techniques of this instrument have been described in detail elsewhere [22]. Briefly, a vacuum pump is used to draw ambient air through a quartz tube around which a UV lamp is mounted. Irradiation with UV light causes particles to emit electrons, which are then captured by surrounding gas molecules. Negatively charged particles are removed from the air stream,

Compound Abbr. Molecular

Indeno(1,2,3-

\*Pa at 20 ºC

formula

**Table 1.** Physico-chemical properties of 13 PAHs measured in this study [2]

**Figure 2.** Measurement locations. a) Rama6; b) Chockchai4 (a) (b)

**Figure 3.** Micro Orifice Uniform Deposit Impactors (MOUDI)

Polytetrafluoroethylene (PTFE) membrane filters of 47-mm diameters (ADVANTEC, Japan) were used as the impaction substrates, and 37-mm glass filters (ADVANTEC, Japan) were used as the after-filter. The aerodynamic diameter size cut points with 50% collection efficiency were 0.18, 0.31, 0.56, 1.0, 1.8, 3.2, 5.6, 10, and 18 μm. The MOUDI operated at 30 L/min, and the particle mass in the filters was determined gravimetrically. Before each weighing, the filters were conditioned in a desiccator with silica gel for about three days to eliminate humidity. Afterward, the filters were wrapped in aluminum foil and stored at 4 °C until the extraction was performed. After ultrasonic extraction, 13 kinds of PAHs with three to six aromatic rings (Table 1 and Figure 4) were determined by Gas Chromatography / Mass Spectrometry (GC/MS) analysis. Among the 13 PAHs, 12 of them, not including Benzo(e)pyrene (BeP), have been included in the priority pollutant list of the Clean Water Act of the United States Environmental Protection Agency (US EPA) since the 1970s.

Temporal Variation of Particle Size Distribution of Polycyclic Aromatic Hydrocarbons at Different Roadside Air Environments in Bangkok, Thailand 33

**Figure 4.** Schematic diagram of a MOUDI stage showing its relation to the above and below stages [19]


#### \*Pa at 20 ºC

32 Atmospheric Aerosols – Regional Characteristics – Chemistry and Physics

**Figure 2.** Measurement locations. a) Rama6; b) Chockchai4

**Figure 3.** Micro Orifice Uniform Deposit Impactors (MOUDI)

Polytetrafluoroethylene (PTFE) membrane filters of 47-mm diameters (ADVANTEC, Japan) were used as the impaction substrates, and 37-mm glass filters (ADVANTEC, Japan) were used as the after-filter. The aerodynamic diameter size cut points with 50% collection efficiency were 0.18, 0.31, 0.56, 1.0, 1.8, 3.2, 5.6, 10, and 18 μm. The MOUDI operated at 30 L/min, and the particle mass in the filters was determined gravimetrically. Before each weighing, the filters were conditioned in a desiccator with silica gel for about three days to eliminate humidity. Afterward, the filters were wrapped in aluminum foil and stored at 4 °C until the extraction was performed. After ultrasonic extraction, 13 kinds of PAHs with three to six aromatic rings (Table 1 and Figure 4) were determined by Gas Chromatography / Mass Spectrometry (GC/MS) analysis. Among the 13 PAHs, 12 of them, not including Benzo(e)pyrene (BeP), have been included in the priority pollutant list of the Clean Water

(a) (b)

Act of the United States Environmental Protection Agency (US EPA) since the 1970s.

**Table 1.** Physico-chemical properties of 13 PAHs measured in this study [2]

To monitor the temporal variations of total concentrations of particulate PAHs, photoelectric aerosol sensors (model PAS2000CE, EcoChem Analytics, Germany) [20] were used for realtime monitoring (Figure 5). Photoelectric aerosol sensors (PAS) work on the basis of photoelectric ionization of PAHs adsorbed onto particles [21]. The measurement techniques of this instrument have been described in detail elsewhere [22]. Briefly, a vacuum pump is used to draw ambient air through a quartz tube around which a UV lamp is mounted. Irradiation with UV light causes particles to emit electrons, which are then captured by surrounding gas molecules. Negatively charged particles are removed from the air stream,

Temporal Variation of Particle Size Distribution of Polycyclic Aromatic Hydrocarbons at Different Roadside Air Environments in Bangkok, Thailand 35

Particle sizes in the atmosphere are known to distribute with certain frequency modes, namely, nuclei mode, accumulation mode and coarse mode [23]. The nuclei mode, or ultrafine mode is mainly primary emission of vehicle exhaust and is carbonaceous particulate matter. The accumulation mode is responsible for formation of secondary organic aerosols especially through photochemical reactions with VOCs including gas phase PAHs and also for coagulation of particles. The coarse mode (>1.8 um) particles are mostly grown particles in the atmosphere and/or re-suspended road dust, which are reported to be subject to condensation of volatile materials including lighter PAHs. From previous studies, concentrations of PAHs are found to be highly dependent upon the size of particles. In view of association mechanisms and atmospheric processes of PAHs to urban aerosols, those particle size modes are applied to this study [7]. Based on previous studies on PAHs measurement using cascade air samplers (e.g., [24-25]) three particle size modes are defined for this study: ultrafine mode (< 0.18 μm), accumulation mode (0.18-1.8 μm) and coarse

Road traffic was recorded using a video camera for 24 hours or shorter during the air sampling. The traffic volume was counted manually for 10 minutes in every hour, then multiplied by six to estimate hourly average volumes. At the CC site, hourly meteorological data monitored by the PCD were obtained. The meteorological data included temperature, solar radiation, relative humidity, rain, wind speed and wind direction. At the R6 site, wind speed and wind directions were monitored at 10-minute intervals using KADEC wind monitors (Kona Systems, Japan), and temperature, solar radiation, relative humidity and rainfall were monitored at 5-minute intervals using an AutoMet meteorology monitor (MET

mode (1.8μm <) according to the particle cut sizes of the MOUDI.

**2.4. Traffic and meteorological data** 

ONE Instruments, USA).

**Figure 7.** Scheme of PAS2000CE [49]

**2.3. Particle size distribution** 

**Figure 5.** Structural formulas of the 13 PAHs

and the remaining positively charged particles are collected on a particle filter mounted in a Faraday cage. The particle filter converts the ion current to an electrical current, which is then amplified and measured with an electrometer (Figure 6). The electric current establishes signals that are proportional to the concentrations of total PAHs [20]. The target particle size is below 1 μm and the signals are recorded every 2 minutes. In the results of this study, PAS monitoring data are indicated as PAS signals without particular units, because the purpose of use of PAS is to know relative levels of temporal variations of total PAH concentrations, not to know absolute values of the total PAH concentrations, for which actual kinds of PAHs which compose the total concentrations cannot be identified by the PAS.

**Figure 6.** PAS2000CE

**Figure 7.** Scheme of PAS2000CE [49]

benzo[k]fluoranthene benzo[e]py rene

**Figure 5.** Structural formulas of the 13 PAHs

**Figure 6.** PAS2000CE

and the remaining positively charged particles are collected on a particle filter mounted in a Faraday cage. The particle filter converts the ion current to an electrical current, which is then amplified and measured with an electrometer (Figure 6). The electric current establishes signals that are proportional to the concentrations of total PAHs [20]. The target particle size is below 1 μm and the signals are recorded every 2 minutes. In the results of this study, PAS monitoring data are indicated as PAS signals without particular units, because the purpose of use of PAS is to know relative levels of temporal variations of total PAH concentrations, not to know absolute values of the total PAH concentrations, for which actual kinds of PAHs

indeno[1,2,3-cd]py rene benzo[ghi]perylene

Dibenz [a,h]anthracene

phenanthrene anthracene py rene

fluoranthene

benzo[a]anthracene benzo[b]fluoranthene

chrysene

benzo[a]py rene

which compose the total concentrations cannot be identified by the PAS.
