Impact of chamber wall loss of gaseous organic compounds on secondary organic aerosol formation: explicit modeling of SOA formation from alkane and alkene oxidation
Recent studies have shown that low volatility gas-phase species can be lost
onto the smog chamber wall surfaces. Although this loss of organic vapors to
walls could be substantial during experiments, its effect on secondary
organic aerosol (SOA) formation has not been well characterized and
quantified yet. Here the potential impact of chamber walls on the loss of
gaseous organic species and SOA formation has been explored using the
Generator for Explicit Chemistry and Kinetics of the Organics in the
Atmosphere (GECKO-A) modeling tool, which explicitly represents SOA formation
and gas–wall partitioning. The model was compared with 41 smog chamber
experiments of SOA formation under OH oxidation of alkane and alkene series
(linear, cyclic and C12-branched alkanes and terminal, internal and 2-methyl
alkenes with 7 to 17 carbon atoms) under high NOx conditions. Simulated
trends match observed trends within and between homologous series. The loss
of organic vapors to the chamber walls is found to affect SOA yields as well
as the composition of the gas and the particle phases. Simulated
distributions of the species in various phases suggest that nitrates,
hydroxynitrates and carbonylesters could substantially be lost onto walls.
The extent of this process depends on the rate of gas–wall mass transfer,
the vapor pressure of the species and the duration of the experiments. This
work suggests that SOA yields inferred from chamber experiments could be
underestimated up a factor of 2 due to the loss of organic vapors to chamber
walls