5977a gas chromatograph

Prior to analysis, isotopically labeled internal standards (Table S4) were added to QFF extract aliquots. Identification and quantification was performed using an Agilent J&W 30 m X 0.25 mm i.d. (0.25μm film thickness) DB-5 capillary column on an Agilent 5977A Gas Chromatograph, coupled to a quadrupole Mass Spectrometry (GC-MS) operated in 70 Volt electron impact ionization mode. Detailed GC-MS methods can be found in supplementary information (SI). Extracts were analyzed using both selected ion monitoring (SIM) mode, to look for and quantify PAHs and PAH-OPs with available analytical standards, and full scan mode (with and without derivatization) to identify unknown peaks that might be associated with other PAH-OPs without available analytical standards. To measure hydroxy substituted PAHs (OHPAHs), derivatization using MTBSTFA for mono-hydroxylated OHPAHs, and BSTFA for poly-hydroxylated OHPAHs, was performed. This process required incubation at 65°C for 25 minutes (MTBSTFA) or 70°C for 45 minutes (BSTFA) and is described in the SI. Mass spectra of GC-MS fragmentation were interpreted using Mass Hunter software. Lab blank PAH or PAH-OP concentrations were subtracted from their measured concentrations, and divided by the total SOA mass collected, to give the weight percent (wt%) of PAH or PAH-OP. We report the mean weight percent ± one standard error (SE).