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.

Automated summary

This study utilized advanced analytical techniques to reduce the unresolved complex mixture (UCM) in intermediate and semi-volatile organic compounds (I/SVOCs) emitted from biomass and coal burning, which significantly impacts the secondary organic aerosol (SOA) formation. The identified major compounds in I/SVOCs contribute significantly to the predicted SOA production for both biomass and coal burning, highlighting the importance of targeting specific chemical components for accurate estimation of environmental impacts.