Source Diversity of Intermediate Volatility n -Alkanes Revealed by Compound-Specific δ 13 C-δD Isotopes.

Intermediate volatility organic compounds (IVOCs) are important precursors of secondary organic aerosols, and their sources remain poorly defined. N -alkanes represent a considerable portion of IVOCs in atmosphere, which can be well identified and quantified out of the complex IVOC pool. To investigate the potential source diversity of intermediate volatility n -alkanes (IVnAs, n C 12 - n C 20 ), we apportioned the sources of IVnAs in the atmosphere of four North China cities, based on their compound-specific δ 13 C-δD isotope compositions and Bayesian model analysis. The concentration level of IVnAs reached 1195 ± 594 ng/m 3 . The δ 13 C values of IVnAs ranged -32.3 to -27.6‰ and δD values -161 to -90‰. The δD values showed a general increasing trend toward higher carbon number alkanes, albeit a zigzag odd-even prevalence. Bayesian MixSIAR model using δ 13 C and δD compositions revealed that the source patterns of individual IVnAs were inconsistent; the relative contributions of liquid fossil combustion were higher for lighter IVnAs ( e.g., n C 12 - n C 13 ), while those of coal combustion were higher for heavier IVnAs ( e.g., n C 17 - n C 20 ). This result agrees with principal component analysis of the dual isotope data. Overall, coal combustion, liquid fossil fuel combustion, and biomass burning contributed about 47.8 ± 0.1, 35.7 ± 4.0, and 16.3 ± 4.2% to the total IVnAs, respectively, highlighting the importance of coal combustion as an IVnA source in North China. Our study demonstrates that the dual-isotope approach is a powerful tool for source apportionment of atmospheric IVOCs.