Significant secondary organic aerosol production from aqueous-phase processing of two intermediate volatility organic compounds

Intermediate volatility organic compounds (IVOCs) recently have been identified as an important group of air pollutants, and they can contribute significantly to the secondary organic aerosol (SOA) formation via gas-phase reactions. However, significance of the SOA from aqueous oxidation of IVOCs was largely unknown. Here, we investigated the aqueous aging of two model IVOCs of naphthoquinone (NAQ) and phenanthrene (PHE) at a staring concentration of 10 mu M. Both species were found to have high SOA yields (similar to 50%) against hydroxyl radical photochemical oxidation. PHE can be slowly oxidized under dark conditions (similar to 10% in 8 h) while NAQ cannot, but it can photo-degrade itself under simulated sunlight at a high rate (similar to 56% in 1 h). A group of oxygenated products were formed and its concentrations increased continuously throughout hydroxyl radical-mediated aging of both precursors. Aqueous aging led to enhancements of light absorption, especially for NAQ, and the oxygenated products were likely light chromophores. Our findings highlight the possible significance of SOA from aqueous oxidation of IVOCs. Future investigations on a broad spectrum of IVOCs and inclusion of such SOA formation pathway into climate and air quality models should be considered.