Humidity influence on gas-particle phase partitioning of α-pinene + O3 secondary organic aerosol

Water vapor uptake to particles could potentially affect organic-aerosol mass in three ways: first, water in the organic phase could reduce organic (equilibrium) partial pressures according to Raoult's law; second, an aqueous phase could attract water soluble organics according to Henry's law; finally, deliquescence of inorganic particle cores could mix the organic and inorganic particle phases, significantly diluting the organics and again reducing organic partial pressures according to Raoult's law. We present experiments using initially dry alpha-pinene + ozone secondary organic aerosol (SOA) on ammonium sulfate (AS) seeds at atmospheric concentrations in a smog chamber. After SOA formation, the chamber relative humidity is increased steadily by addition of steam to near 100%. Little subsequent SOA mass growth is observed, suggesting that none of these potential effects play a strong role in this system. Citation: Prisle, N. L., G. J. Engelhart, M. Bilde, and N. M. Donahue (2010), Humidity influence on gas-particle phase partitioning of alpha-pinene + O-3 secondary organic aerosol, Geophys. Res. Lett., 37, L01802, doi: 10.1029/2009GL041402.