An alternative semi-quantitative GC/MS method to estimate levels of airborne intermediate volatile organic compounds (IVOCs) in ambient air

Abstract

Abstract Intermediate volatile organic compounds (IVOCs) have attracted much attention due to their contributions to the formation of secondary organic aerosol (SOA) in ambient air. Determination of total IVOCs in ambient air is therefore important for assessing their roles in air pollution. Currently, concentrations of IVOCs are estimated using a previously published semi-quantitative method. In this paper we propose an alternative method for the determination of IVOCs concentrations, in which speciated IVOCs of n-alkanes, polycyclic aromatic hydrocarbons (PAHs) and phthalates are treated as speciated IVOCs and quantified using their respective standards. The ion signal attributed to the speciated IVOCs is then subtracted from the total ion chromatogram (TIC) and the remaining peak area is used to semi-quantitatively estimate the remaining mass regarded as unspeciated complex mixture (UCM) IVOCs. The TIC peak area of speciated IVOCs in ambient air samples is reconstructed based on the peak area ratio of extracted ion chromatogram (EIC) of the quantifying ion and the TIC from their respective standards. The total IVOCs is then calculated as the sum of the speciated IVOCs and the UCM IVOCs. Twenty-one ambient air samples, collected from November 7 to December 12, 2018 in the urban area of Shanghai, were used to compare our method with the previously published method. Although the overall differences in UCM IVOCs and total IVOCs values were small between the two methods, different values of UCM IVOCs and total IVOCs in several sections of the chromatogram that contain phthalates were observed. Analysis of the ambient air samples also revealed that levels of IVOCs were significantly correlated with atmospheric PM2.5. Our method has the advantage that more accurate results in the determination of total IVOCs can be achieved when more compounds are identified and added to the list of speciated IVOCs.