Atmospheric polycyclic aromatic hydrocarbons (PAHs) in Asia: A review from 1999 to 2004

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are present in both gaseous and particulate phases. These compounds are considered to be atmospheric contaminants and are human carcinogens. Many studies have monitored atmospheric particulate and gaseous phases of PAH in Asia over the past 5 years. This work compares and discusses different sample collection, pretreatment and analytical methods. The main PAH sources are traffic exhausts (AcPy, FL, Flu, PA, Pyr, CHR, BeP) and industrial emissions (BaP, BaA, PER, BeP, COR, CYC). PAH concentrations are highest in areas of traffic, followed by the urban sites, and lowest in rural sites. Meteorological conditions, such as temperature, wind speed and humidity, strongly affect PAH concentrations at all sampling sites. This work elucidates the characteristics, sources and distribution, and the healthy impacts of atmospheric PAH species in Asia.

Introduction

This review study summarizes the emission characteristics, sources, sampling and analysis methods of polycyclic aromatic hydrocarbons (PAHs) in the Asian countries Thailand, Malaysia, China, Korea, Japan and Taiwan. Although these countries have similar atmospheric conditions—quite sunny and mild—the intensity of traffic, energy consumption and energy generation vary widely (Mastral et al., 2003).

PAHs are formed from the incomplete combustion or pyrolysis of organic material such as oil, petroleum gas, coal, and wood, which are usually used in energy production. Tobacco smoking also increases the ambient levels of PAHs in air, and the use of heating devices can increase the concentrations of PAHs indoors (WHO, 1987). PAHs have attracted much attention in the studies on air pollution recently because some of them are highly carcinogenic or mutagenic. In particular, benzo[a]pyrene (BaP) has been identified as a highly carcinogenic compound. Reliable sampling and analytical methods are necessary to measure the extent of human exposure to Bap and other PAHs (US EPA, 1999). Although atmospheric PAHs can be present in particulate or gaseous matters, they are associated predominantly with particulate matters. Particle-bond PAHs (p-PAHs) are considered to be the most hazardous substances to human health. From the view of this health concern, monitoring the levels of p-PAHs in urban areas is very important (Chetwittachan et al., 2002). The highest concentrations of atmospheric PAHs are usually found in urban areas due to the increasing vehicular traffic and the scarce dispersions of atmospheric pollutants. The risk associated with human exposure to atmospheric PAHs is highest in the urban because of the density of population (Caricchia et al., 1999). Despite the drastic reduction of urban particulate pollution in cities caused by the burning of coal and a shift toward other fossil fuels (oil or natural gas) for domestic heating, the increasing population and traffic have all contributed to the gradually more serious particulate pollution in the cities. In addition, particles produced by cars are much smaller than coal particles and are found in the breathable size fraction (Manoli et al., 2002). Most studies have provided more information on the multi-ringed heavier PAHs rather than the lighter ones. These lighter PAH compounds have less carcinogenic or mutagenic properties; however, they are most abundant in the urban atmosphere and react with other pollutants to form more toxic derivatives (Park et al., 2002).

The concentrations of the following PAHs were studied and their elution orders in GC/MS analyses follow the sequences of naphthalene (Nap, m/z 128), acenaphthylene (AcPy, m/z 152), acenaphthene (Acp, m/z 154), fluorene (Flu, m/z 166), phenanthrene (PA, m/z 178), anthracene (Ant, m/z 178), fluoranthene (FL, m/z 202), pyrene (Pyr, m/z 202), cyclopenta[c,d]pyrene (CYC, m/z 226), benzo[a]anthracene (BaA, m/z 228), chrysene (CHR, m/z 228), benzo[b]fluoranthene (BbF, m/z 252), benzo[k]fluoranthene (BkF, m/z 252), benzo[e]pyrene (BeP, m/z 252), benzo[a]pyrene (BaP, m/z 252), perylene (PER, m/z 252), indeno[1,2,3,-cd]pyrene (IND, m/z 276), dibenzo[a,h]anthracene (DBA, m/z 278), benzo[b]chrycene (BbC, m/z 278), benzo[g,h,i]perylene (BghiP, m/z 276) and coronene (COR, m/z 300) (Fang et al., 2004a, Fang et al., 2004b).

In the past, chimney sweeps suffered from skin cancers and scrotal cancers due to higher dermal exposure in the PAH compounds. Epidemiological studies have been conducted among workers exposed at coke ovens in coal coking, coal gasification, asphalt, foundries, and aluminum production plants. Workers who are exposed to diesel exhaust have also been investigated (Partanen and Boffetta, 1994, Costantino et al., 1995). People in all listed occupations are also exposed to other chemicals, making a direct correlation between increased levels of PAHs and lung cancer problematic. Only a few animal tests have addressed the ingestions of PAHs. BaA, BaP, DBA, and mixtures of PAHs (coal tar) were carcinogenic (WHO, 1998). Some of the PAH species are known to be animal and/or human carcinogens, so evaluating the healthy risk that is associated with the exposure to both particulate PAHs and gaseous PAHs is important. Gaseous PAHs usually contain more fractions of less carcinogenicity and lower molecular weights, while particulate PAHs contain more fractions of higher carcinogenicity and higher molecular weights. In principle, PAHs with high molecular weights are often more carcinogenic than those with low molecular weights (Park et al., 2002, Tsai et al., 2002). With these biochemical and carcinogenic properties of PAHs, the PAHs present in surrounding air have direct impacts on human population. For example, mortality due to lung cancer is increasing in developed countries. Thus, a survey of PAHs levels in indoor and outdoor air is an important as a part of risk assessment and management associated with these chemicals (Liu et al., 2001).

In 1987, the U.S. Environmental Protection Agency (EPA) promulgated a new size-specific air quality standard for environmental particulate matter (US EPA, 1999). This new standard applies only to particles with aerodynamic diameters of smaller than or equal to 10 μm (PM₁₀) and replaces the original standard for the total suspended particles (TSP). PM_2.5 and aerosols with a diameter of 1.0 μm or less are now being taken into consideration because these particles can be inhaled into the deeper respiratory tract regions. Moreover, PAHs are concentrated in the submicron particulate matter by the condensations of gaseous PAHs. Many problems affect the samplings and measurements of atmospheric PAHs:

• PAHs are emitted in a very complex matrix;

• Many studies cannot be compared because different analytic techniques caused different results. PAHs with very low concentrations can only be detected using highly sensitive analytical methods which are not suitable for larger quantities and vice versa;

• Most approaches to atmospheric PAHs sampling use filters and adsorbents to catch particular and gaseous PAHs, which are not suitable for the other volatile species; also, other species cannot be completely extracted once adsorbed;

• PAHs deposition with the PM greater than 3–5 μm and/or gaseous PAHs re-volatilization may follow deposited;

• strong influences of the meteorological conditions;

• strong influences of the ambient contaminants;

• others.

This work attempts to discuss the atmospheric PAH data from Asia to help understand the sources, distributions of PAH species and the impact of atmospheric PAH on health in Asian countries.