Addressing Unresolved Complex Mixture of I/SVOCs Emitted From Incomplete Combustion of Solid Fuels by Nontarget Analysis

The major fraction of intermediate and semi-volatility organic compounds (I/SVOCs) is still unresolved by traditional analyses, leaving large unresolved complex mixture (UCM) and limiting the estimation of secondary organic aerosol (SOA). This study addressed the UCM by employing two-dimensional gas chromatography-time-of-flight mass spectrometry. The ratios of UCM in I/SVOCs emitted from household burning of biomass and coal were reduced to 1.0 +/- 0.3% and 2.1 +/- 2.0%, respectively, and these levels are one order of magnitude less than those reported in previous studies. Phenols, polycyclic aromatic hydrocarbons, and ketones made the major contribution to I/SVOCs emission factors (EFs) (65.9 +/- 9.6%) for biomass burning, while amides, acids, and esters constituted the majority of EFs (56.5 +/- 45.0%) for coal burning. Furthermore, SOA production can be predicted via the highly identified I/SVOCs compounds based on volatility distributions of each speciated species. These majority compounds contribute the predicted SOA production with 76.0 +/- 12.7% and 82.0 +/- 60.3% for biomass and coal burning, respectively. Underestimated SOA production with the ratio of 62.5 +/- 25.2% to 80.9 +/- 2.8% via previous Bins method has been well addressed. The obtained results suggest that the nontarget analysis can significantly improve the accuracy of I/SVOCs estimation and environmental impacts by addressing chemical components at the molecular level.