Chromatographic differentiation in SOA fingerprint identification: A study on naphthalene and α-pinene oxidation

The evolution of precursors to form secondary organic aerosol (SOA) is still a challenge in atmospheric chemistry. Chamber experiments were conducted to simulate the ambient OH oxidation of naphthalene and α-pinene, which are typical markers of anthropogenic and biogenic emissions. Particulate matters were sampled by quartz filters and were analyzed by comprehensive two-dimensional gas chromatography (GC×GC) coupled with a thermal desorption system (TD) and a mass spectrometer (MS). A four-step procedure is proposed based on chromatographic differentiation in SOA fingerprint identification, including initial resolving, translation and alignment, pixel-based differentiation, and marker identification. Data processing begins by creating a 65-organic consensus template from peak identification results. Peaks are screened with matching factors >700. Retention time shifts of Naphthalene and α-pinene oxidation products are 0.5 min and 0.1 min respectively. A reverse matching factor >800 is used to define high-confidence compound recognition, and the ±50 retention index tolerance assists structure ID for SOA study. Two new markers are found for the first time, i.e., phthalimide in naphthalene-OH oxidation with the occurrence of NO_x, and citronellol epoxide from α-pinene-OH oxidation. Our finding offers fresh insights into the complex chemical pathways of these precursors and improving our understanding of SOA formation mechanisms. Our workflow works well for fingerprint identification and could be utilized in finding SOA intermediates and source appointments.