Abstract
Abstract. Size-segregated (9 stages) n-alkanes, polycyclic aromatic hydrocarbons (PAHs) and hopanes in the urban (Baoji city in inland China), mountain (Mt. Tai in east coastal China) and marine (Okinawa Island, Japan) atmospheres over East Asia were studied using a GC/MS technique. Ambient concentrations of n-alkanes (1698±568 ng m−3 in winter and 487±145 ng m−3 in spring), PAHs (536±80 and 161±39 ng m−3), and hopanes (65±24 and 20±2.4 ng m−3) in the urban air are 1–2 orders of magnitude higher than those in the mountain aerosols and 2–3 orders of magnitude higher than those in the marine samples. Mass ratios of n-alkanes, PAHs and hopanes clearly demonstrate coal-burning emissions as their major source. Size distributions of fossil fuel derived n-alkane, PAHs and hopanes were found to be unimodal in most cases, peaking at 0.7–1.1 μm size. In contrast, plant wax derived n-alkanes presented a bimodal distribution with two peaks at the sizes of 0.7–1.1 μm and >4.7 μm in the summer mountain and spring marine samples. Among the three types of samples, geometric mean diameter (GMD) of the organics in fine mode (<2.1 μm) was found to be smallest (av. 0.63 μm in spring) for the urban samples and largest (1.01 μm) for the marine samples, whereas the GMD in coarse mode (≥2.1 μm) was found to be smallest (3.48 μm) for the marine aerosols and largest (4.04 μm) for the urban aerosols. The fine mode GMDs of the urban and mountain samples were larger in winter than in spring and summer. Moreover, GMDs of 3- and 4-ring PAHs were larger than those of 5- and 6-ring PAHs in the three types of atmospheres. Such differences in GMDs can be interpreted by the repartitioning of organic compounds and the coagulation and hygroscopic growth of particles during a long-range transport from the inland continent to the marine area, as well as the difference in their sources among the three regions.
Highlights
Atmospheric aerosols influence climate directly by scattering and absorbing radiation, and indirectly by modifying the optical properties and lifetime of clouds via acting as cloud condensation nuclei (Albrecht, 1989; Ramanathan, 2001)
The total suspended particle (TSP)-equivalent concentrations of the compounds determined in Baoji city are 1–2 orders of magnitude higher than those in the mountain samples and 2–3 orders of magnitude higher than those in the marine samples
Concentration ratios and compositions of the organics indicate that coal combustion in China is the major source of airborne particulate polycyclic aromatic hydrocarbons (PAHs) over East Asia
Summary
Atmospheric aerosols influence climate directly by scattering and absorbing radiation, and indirectly by modifying the optical properties and lifetime of clouds via acting as cloud condensation nuclei (Albrecht, 1989; Ramanathan, 2001). Few studies on size distributions of organic aerosols were sparsely conducted for n-alkanes, PAHs and carboxylic acids in economically developed coastal cities in China such as Hong Kong (Yu et al, 2004; Huang et al, 2006; Zheng et al, 2008), Guangzhou (Bi et al, 2005; Duan et al, 2007) and Beijing (Yao et al, 2003). In order to investigate the similarity and differences in the chemical compositions and size distributions of aerosols from different atmospheric environments in East Asia, we have characterized size-segregated atmospheric particles from Baoji (an inland Chinese city), Mt. Tai (China) and Okinawa Island (Japan). In the current paper we first present concentrations, compositions, and sources of particulate organic compounds (i.e. n-alkanes, PAHs and hopanes) in the three types of atmospheric environments, and characterize their detailed size distributions on a molecular level
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