Frontier review on comprehensive two-dimensional gas chromatography for measuring organic aerosol

Organic aerosol (OA) is a key component of atmospheric fine particles and can be composed of thousands of organic species, creating an analytical challenge to separate and identify such highly complex mixtures. Traditional offline one-dimensional gas chromatography, mostly separating molecules based on volatility, provides valuable information on the composition of OA, but is limited by insufficient separation and low peak capacity. Since its introduction in 1990s, comprehensive two-dimensional gas chromatography (GC × GC), which separates molecules by both volatility and polarity, has become an effective tool to determine the OA composition through its high molecular separation resolution and high peak capacity. Both online and offline GC × GC analyses have been applied to study OA, which extended the identification of unknown compounds and the quantification of a larger range of target compounds. Here, we review the studies using GC × GC for analyzing OA from both the ambient environment and source emissions. GC × GC coupled with mass spectrometry provides a variety of novel analysis methods, demonstrating the power of GC × GC analyzing complex aerosol samples. The development of online technologies in recent years helps to capture the dynamic temporal variations of atmospheric OA due to changes in source emissions as well as atmospheric secondary formation and meteorology.