Multi-generation chemical aging of α-pinene ozonolysis products by reactions with OH

Secondary organic aerosol (SOA) formation from volatile organic compounds (VOCs) in the atmosphere can be thought of as a succession of oxidation steps. The production of later-generation SOA via continued oxidation of the first-generation products is defined as chemical aging. This study investigates aging in the alpha-pinene ozonolysis system with hydroxyl radicals (OH) through smog chamber experiments. The first- generation alpha-pinene ozonolysis products were allowed to react further with OH formed via HONO photolysis. After an equivalent of 2-4 days of typical atmospheric oxidation conditions, homogeneous OH oxidation of the alpha-pinene ozonolysis products resulted in a 20-40% net increase in the SOA for the experimental conditions used in this work. A more oxygenated product distribution was observed after aging based on the increase in aerosol atomic oxygen-to-carbon ratio (O : C) by up to 0.04. Experiments performed at intermediate relative humidity (RH) of 50% showed no significant difference in additional SOA formation during aging compared to those performed at a low RH of less than 20 %.