Size-distributions of n-alkanes, PAHs and hopanes and their sources in the urban, mountain and marine atmospheres over East Asia

摘要

Size-segregated (9 stages) -alkanes, polycyclic aromatichydrocarbons (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. Ambientconcentrations of -alkanes (1698±568 ng m in winter and487±145 ng m in spring), PAHs (536±80 and 161±39 ng m),and hopanes (65±24 and 20±2.4 ng m) in theurban air are 1–2 orders of magnitude higher than those in the mountainaerosols and 2–3 orders of magnitude higher than those in the marinesamples. Mass ratios of -alkanes, PAHs and hopanes clearly demonstratecoal-burning emissions as their major source. Size distributions of fossilfuel derived -alkane, PAHs and hopanes were found to be unimodal in mostcases, peaking at 0.7–1.1 μm size. In contrast, plant wax derived-alkanes presented a bimodal distribution with two peaks at the sizes of0.7–1.1 μm and 4.7 μm in the summer mountain and springmarine samples. Among the three types of samples, geometric mean diameter(GMD) of the organics in fine mode (2.1 μm) was found to besmallest (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 themarine aerosols and largest (4.04 μm) for the urban aerosols. The finemode GMDs of the urban and mountain samples were larger in winter than inspring and summer. Moreover, GMDs of 3- and 4-ring PAHs were larger thanthose of 5- and 6-ring PAHs in the three types of atmospheres. Suchdifferences in GMDs can be interpreted by the repartitioning of organiccompounds and the coagulation and hygroscopic growth of particles during along-range transport from the inland continent to the marine area, as wellas the difference in their sources among the three regions.