Abstract View
Aqueous-phase Brown Carbon Formation from Limonene SOA: Effects of Drying Conditions and Gas-phase Precursors
NETHMI KASTHURIARACHCHI, Laura-Helena Rivellini, Alex Lee, National University of Singapore
Abstract Number: 288
Working Group: Aerosol Chemistry
Abstract
Aqueous-phase processing of secondary organic aerosols (SOA) can produce light absorbing organic species, commonly referred to as brown carbon (BrC), via reactions with reduced nitrogen species. While many previous studies have investigated BrC forming reactions of SOA from limonene ozonolysis (limonene SOA) with reduced nitrogen species in bulk solutions, little is known about their formation behaviour in aerosol droplets. This work shows that BrC formation is substantially accelerated upon drying of limonene SOA and ammonium sulfate/glycine mixed droplets. Although water evaporation has been shown to continuously enhance the absorptivity in aqueous bulk solutions, the results show that the mass absorption efficiency (MAE, m2/gC) of prominent absorbance peaks were highest at ~75% relative humidity (RH) and then decreased at lower RH conditions. Furthermore, absorbance at longer wavelengths (500-520nm), which are the strongest peaks in evaporated bulk solutions, were diminished in evaporated droplets. We hypothesise that rapid re-partitioning of semi-volatile BrC precursors in limonene SOA may occur upon drying, limiting the multi-step oligomerisation mechanism for producing BrC with longer wavelength absorption. Further investigation shows that generating limonene SOA in the presence of other anthropogenic or biogenic volatile organic compounds (VOC) can enhance BrC formation during subsequent drying of bulk SOA extracts mixed with ammonium suflate/glycine. These observations highlight the potential effects of anthropogenic-biogenic interactions on SOA compositions that can subsequently affect secondary BrC formation via aqueous-phase processing.