Comment on "Semiempirical model for organic aerosol growth by acid-catalyzed heterogeneous reactions of carbonyls".

Jang et al. (1) report measurements of organic particulate matter (OPM) formed in the presence of acidic seed aerosols using both a flow reactor and a Teflon chamber and examine their data using two modeling approaches. The study is a continuation of work by Jang et al. (2) on whether acidity in atmospheric PM can promote the formation of OPM by “heterogeneous” reaction of a variety of relatively volatile (C5-C10) aldehydes and ketones. Jang et al. (1) state that (a) “no predictivity power was achieved” for their experimental systems when using the absorptive partitioning model of Pankow (3) and (b) “These results suggest that semiempirical approaches can vastly improve our ability to predict the organic aerosol growth of a variety of different carbonyls in the presence of inorganic acid. For equilibrium conditions in the atmosphere this approach can be applied directly.” In our view, (a) Jang et al. (1) misapplied the Pankow (3) model and (b) their proposed “semiempirical model” is inherently a characterization of the kinetics of OPM formation (see their eqs 5-12) under specific conditions and so is not easily applicable to the prediction of how much OPM will form under other kinetic conditions and certainly not at equilibrium in the atmosphere. Organic aerosol formation yield Y is typically defined as (e.g., see ref 4)