Secondary aerosol formation from the oxidation of toluene by chlorine atoms

Oxidation of toluene by chlorine atoms (Cl) was studied in a chamber. Secondary organic aerosol (SOA) yields ranged from 3.0 to 7.9% for aerosol concentrations up to 12.0 μg m−3. SOA yields from toluene/Cl reactions and model parameters related to aerosol growth depend on the initial ratio of molecular chlorine to toluene. Data from an Aerodyne quadrupole Aerosol Mass Spectrometer (Q-AMS) indicate that a small fraction of the generated aerosol mass is inorganic chloride (approximately 4%), that inorganic chloride aerosol growth ceases contemporaneously with that of SOA, and that particles are mixed internally. Analysis of Q-AMS spectra indicates predominance of species that traditionally are thought to be representative of SOA but with increased importance of aromatic/ring-retaining products. Mechanistic modeling of the toluene system indicates that final SOA products likely result from the oxidation of quinone type compounds derived via oxidation of the first-generation product benzaldehyde. Zero-dimensional calculations indicate Cl-initiated oxidation could be as important as hydroxyl-radical-initiated oxidation in SOA formation from toluene in early morning in certain coastal or industrialized areas.