Ozonolysis of α-pinene: parameterization of secondary organic aerosol mass fraction

Abstract

Existing parameterizations tend to underpredict the α-pinene aerosol mass fraction (AMF) or yield by a factor of 2–5 at low organic aerosol concentrations (<5 µg m^−3). A wide range of smog chamber results obtained at various conditions (low/high NO_x, presence/absence of UV radiation, dry/humid conditions, and temperatures ranging from 15–40°C) collected by various research teams during the last decade are used to derive new parameterizations of the SOA formation from α-pinene ozonolysis. Parameterizations are developed by fitting experimental data to a basis set of saturation concentrations (from 10^−2 to 10⁴ µg m^−3) using an absorptive equilibrium partitioning model. Separate parameterizations for α-pinene SOA mass fractions are developed for: 1) Low NO_x, dark, and dry conditions, 2) Low NO_x, UV, and dry conditions, 3) Low NO_x, dark, and high RH conditions, 4) High NO_x, dark, and dry conditions, 5) High NO_x, UV, and dry conditions. According to the proposed parameterizations the α-pinene SOA mass fractions in an atmosphere with 5 µg m^−3 of organic aerosol range from 0.032 to 0.1 for reacted α-pinene concentrations in the 1 ppt to 5 ppb range.