Particle wall-loss correction methods in smog chamber experiments
Abstract. The interaction of particles with the chamber walls has been a
significant source of uncertainty when analyzing results of secondary organic
aerosol (SOA) formation experiments performed in Teflon chambers. A number of
particle wall-loss correction methods have been proposed including the use of
a size-independent loss rate constant, the ratio of suspended organic mass to
that of a conserved tracer (e.g., sulfate seeds), and a size-dependent loss rate
constant, etc. For complex experiments such as the chemical aging of SOA, the
results of the SOA quantification analysis can be quite sensitive to the
adopted correction method due to the evolution of the particle size
distribution and the duration of these experiments. We evaluated the performance of several particle wall-loss correction methods
for aging experiments of α -pinene ozonolysis products. Determining
the loss rates from seed loss periods is necessary for this system because it
is not clear when chemical reactions have been completed. Results from the
OA  ∕  sulfate ratio and the size-independent
correction methods can be influenced significantly by the size dependence of
the particle wall-loss process. Coagulation can also affect the particle size
distribution, especially for particles with diameter less than 100 nm, thus
introducing errors in the results of the wall-loss correction. The
corresponding loss rate constants may vary from experiment to experiment, and
even during a specific experiment. Friction between the Teflon chamber walls
and non-conductive surfaces can significantly increase particle wall-loss
rates and the chamber may require weeks to recover to its original condition.
Experimental procedures are proposed for the characterization of particle
losses during different stages of these experiments and the evaluation of
corresponding particle wall-loss correction.