Time-resolved growth behavior of acid aerosols in ethanol vapor with a tandem-DMA technique

We have studied the growth behavior of citric acid, tartaric acid, adipic acid and ammonium bisulfate particles in ethanol vapor with an organic tandem differential mobility analyzer technique (OTDMA). Time dependence of the change in the particle size due to interaction with ethanol vapor was determined. The results show that adipic acid particles have normal deliquescence-hysteresis type of growth behavior, whereas the growth of the other particle types is strongly time dependent due to chemical reactions with timescales on the order of seconds. Citric acid and tartaric acid obviously undergo auto-protonation catalyzed esterification due to their favorable molecular structure, whereas adipic acid has unfavorable structure for intramolecular catalysis. As a rather strong acid, ammonium bisulfate can transfer a proton to ethanol and hence a sulfate esterification reaction takes place. We suggest that time dependent growth behavior can be used for detection of acidic species in atmospheric aerosols.