Molecular distributions and compound-specific stable carbon isotopic compositions of lipids in wintertime aerosols from Beijing.

Lujie Ren,Jing Chen,Pingqing Fu,Juzhi Hou,Chandra Mouli Pavuluri,Yele Sun,Zifa Wang,Yue He

doi:10.1038/srep27481

Abstract

Molecular distributions and stable carbon isotopic compositions (δ13C) of n-alkanes, fatty acids and n-alcohols were investigated in urban aerosols from Beijing, northern China to better understand the sources and long-range atmospheric transport of terrestrial organic matter during polluted and clear days in winter. n-Alkanes (C19–C36), fatty acids (C8–C32) and n-alcohols (C16–C32) detected in Beijing aerosols are characterized by the predominance of C23, C16 and C28, respectively. Carbon preference index (CPI) values of n-alkanes, the ratios of the sum of odd-numbered n-alkanes to the sum of even-numbered n-alkanes, are close to 1, indicating a heavy influence of fossil fuel combustion. Relatively higher ratios of C(18:0+16:0)/C(18:n+16:1) (fatty acids) on clear days than polluted days indicate that long-distance transport and/or photochemical aging are more significant during clear days. δ13C values of n-alkanes and low molecular weight fatty acids (C16:0, C18:0) ranged from –34.1 to −24.7% and −26.9 to −24.6%, respectively, which are generally heavier on polluted days than those on clear days. Such a wide range suggests that atmospheric lipids in Beijing aerosols originate from multiple sources and encounter complicated atmospheric processes during long-range transport in North China.

Highlights

The resuspension of decaying plant leafs in soils into the atmosphere, or injected as smoke particles by biomass burning[2,20]
A previous study discriminated among the δ13C values from the rural versus agricultural soils, street dust, soot from vehicles and volcanic dust of PM2.5 and PM10, and the results indicate that δ13C values in particles of different size ranging from the same origin were essentially the same[30]
Kawamura et al.[31] evaluated the contributions of modern/fossil carbon and marine/terrestrial organic matter with the method of stable isotopes; the result suggested that low molecular weight (LMW) fatty acids are predominantly from algal sources whereas HMW fatty acids are mainly derived from terrestrial C3 higher plants

Summary

Results and Discussion

The C18:0/C16:0 ratios in our study showed average values of 0.84 in the daytime versus 0.83 in the nighttime (Table 1), implying a strong input from cooking, road dust, and/or vehicle emissions for both C16:0 and C18:0 in Beijing Both biogenic and anthropogenic emissions are main sources of fatty acids in the atmosphere. Normal fatty alcohols (C16–C32) were detected in the aerosol samples with a concentration range of 24.1–612 ng m−3 (109 ng m−3) in the daytime and 18.8–613 ng m−3 (190 ng m−3) in the nighttime (Tables 1 and S1), the diurnal variations did not show statistical significance (Table S2) Fatty acids Conc. (ng m−3) CPIa C18:0/C16:0 Csat/Cunsat LMW/HMW III. n-Alcohols Conc. (ng m−3) CPIa HMW/LMW

Mean SD

Ihigh Chigh

Materials and Methods

Additional Information