Size-distributions of n-hydrocarbons, PAHs and hopanes and their sources in the urban, mountain and marine atmospheres over East Asia
1State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China
2Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan
3School of the Environment, State Key Laboratory of Pollution Control and Resources Reuse, Nanjing University, Nanjing 210093, China
4Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
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. 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 the major source of the determined organic aerosols. Size distributions of fossil fuel derived n-alkane, PAHs and hopanes were found as a unimodal in most cases, peaking at 0.7–1.1 μm size. In contrast, plant wax derived n-alkanes present 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 determined organics in fine mode (<2.1 μm) was the smallest (av. 0.63 μm in spring) in the urban samples and the largest (1.01 μm) in the marine samples, whereas the GMD in coarse mode (≥2.1 μm) was smallest (3.48 μm) in the marine aerosols and largest (4.04 μm) in the urban aerosols. The fine mode of GMDs in 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 5- and 6-ring PAHs in the three types of atmospheres. Such differences in GMDs may be interpreted by coagulation and repartitioning of organic compound during a long range transport from the inland continent to the marine site, suggesting that the size changes arising from these physical processes must be included in climate models in relevant to organic aerosols.