An online method for monitoring atmospheric intermediate volatile organic compounds with a thermal desorption-gas chromatography/mass spectrometry.

As one of important precursors of secondary organic aerosol (SOA), intermediate volatile organic compounds (IVOCs) have attracted much attention in recent years. Most of the previous studies however largely focused on characteristics of IVOCs from different emission sources, while data from field observations to study their temporal variations was limited for lacking the sufficient time resolution monitoring data. In this study, an online thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) method was developed to generate monitor data with a three-hour time resolution for gaseous atmospheric IVOCs. The method used two multi-sorbent traps that alternated for conducting sample collection and sample analysis. Compounds of CC n-alkanes and 2-4 ring PAHs were chosen as surrogates to evaluate the performance of this method. Regression coefficients of external calibration curves were greater than 0.93 and 0.96 for all individual n-alkanes and PAHs, respectively. Average relative standard deviation (RSD) values among replicate samples spiked at 3 ng for each individual standard were 9% ± 5%. The detection limits of this method for individual n-alkanes and PAHs were 3.1-16.2 ng/m and 1.0-2.7 ng/m, respectively. Atmospheric IVOCs were continuously monitored from September 28 to 30 and October 22 to November 9 in 2018, in an urban area of Shanghai. Besides targeted n-alkanes and PAHs, unspeciated complex mixtures (UCM) of IVOCs as well as total-IVOCs concentrations in the atmosphere were also determined. Measured concentrations and compositions of gaseous IVOCs in the atmosphere in this study were comparable to other similar studies.