Sampling artifacts in denuders during phase partitioning measurements of semi-volatile organic compounds

The partitioning of semi-volatile organic compounds (SVOCs) between the gas and particle phase plays an important role in understanding the formation of secondary organic aerosols (SOAs) in the atmosphere. There are uncertainties and problems associated with measurements during the simultaneous sampling of both gas and particle phases. In recent studies, diffusion denuders have been used for separate sampling of gas and particle phases of organic compounds. The removal of the gaseous species in the denuder distorts the gas–particle equilibrium and leads to the dissociation of the particulate phase during the sampling. This phenomenon is particularly true for volatile organic species and leads to significant error in determining gas-to-particle phase partitioning of organic aerosols due to underestimation of the particle phase. In this study, a model for simultaneous gas diffusion and aerosol decomposition/evaporation in the parallel plate denuder was developed to investigate the effects of sampling artifacts on gas–particle partitioning measurements of SVOCs. The model equations were cast into dimensionless form for generalization, and the effects of governing dimensionless groups on the denuder sampling artifacts were evaluated by performing a sensitivity analysis. Also, regression correlations for denuder sampling artifacts as the function of governing dimensionless groups were obtained. It was observed that the sampling of SVOCs could result in substantial particulate phase loss due to evaporation in the denuder, resulting in significant errors in the phase partitioning measurements. Also, the operating conditions for the denuder, so that the denuder sampling artifacts lie within tolerable limits, were evaluated.

Copyright © 2018 American Association for Aerosol Research