Abstract
The rate of dry deposition of polycyclic aromatic hydrocarbons (PAHs) depends on the size of the particulate matter on which they are adsorbed. The distribution of PAHs on size-fractionated aerosol samples has been studied during winter and in the absence of precipitation to estimate the dry deposition flux of individual PAHs. Size-fractionated ambient particulate matter samples were collected during a 72-hour period, using an eight-stage cascade impactor. Filter paper samples were then extracted ultrasonically, and PAH characterization and quantification performed with a high-performance liquid chromatograph (HPLC) system with UV-visible detector. Total PAH concentrations associated with the size-segregated ambient particulate matters collected on different impactor stages were in the range of 18.3 to 66.6 ng/m3. The size distribution of atmospheric total PAHs was found to be bimodal. The modeled deposition velocity (Vd,i) at the sampling site for the particle size range of < 0.4 µm, 0.4-1.1 µm, 1.1-3.3 µm and 3.3-9.0 µm were found to be 0.004 cm/sec, 0.037 cm/sec, 0.283 cm/sec and 2.72 cm/sec, respectively. The dry deposition flux for individual PAHs at the sampling site was found to be in the range of 0.17 μg/m2/day-2.69 μg/m2/day. The results indicate that the dry deposition of PAHs is mainly due to gravitational settling of coarse particulates.
Highlights
Concentrations of particulate matter in the compounds found in ambient particulate matter and shown by several investigators to be carcinogenic and/or mutagenic (Horikawa et al, 1991; Larsen and Larsen, 1998)
The concentrations of perylene and benzo(ghi)perylene have not shown any dependence on particle size. These polycyclic aromatic hydrocarbons (PAHs) were mostly associated with fine particles, but the lower molecular weight PAH compounds (2-4 rings compounds) predominated in the aerosol fraction > 1.1 μm, whereas the higher molecular weight PAH compounds were predominant in the aerosol fractions < 1.1 μm
It was found that most of the PAHs were associated with fine particles
Summary
Concentrations of particulate matter in the compounds found in ambient particulate matter and shown by several investigators to be carcinogenic and/or mutagenic (Horikawa et al, 1991; Larsen and Larsen, 1998). It is well known that they are formed by pyrolysis of organic material arising mainly from anthropogenic emissions in urban areas, essentially by the combustion of fossil fuels (Benner et al, 1989; Baek et al, 1991). These compounds are usually emitted in the gas phase, but in the free atmosphere they are found, with the exception of naphthalene and tricyclic PAHs, mainly in particulate form. In the absence of precipitation, dry deposition determines the atmospheric residence time of PAHs. The rate of dry deposition depends on the size of the particulate matter on which the PAHs are adsorbed. Characterization and quantification of PAHs in size-segregated aerosol samples are important to evaluate, their residence time in the atmosphere (Sheu et al, 1996)
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