AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Evaluation of Sampling Artifacts in Phase Partitioning Measurements of Semi-Volatile Organic Compounds in Denuders
SUKRANT DHAWAN, Pratim Biswas, Washington University in St Louis
Abstract Number: 345 Working Group: Instrumentation and Methods
Abstract The partitioning of semi-volatile organic compounds (SVOCs) between gas and particle phase plays an important role in the formation of secondary organic aerosols (SOAs) in the atmosphere. However, it is not well understood due to the uncertainties and problems associated with the simultaneous sampling of both gas and particle phases. In the recent studies, semi-volatile thermal desorption aerosol gas chromatograph (SV-TAG) has been used for in situ measurements of organic compounds in both gas and particle phases. In SV-TAG, ambient air is sampled with and without the denuder installed at the sample inlet. The denuder removes gas phase from the sample stream and provides organic species in the particle phase. Whereas, the sample without denuder provides the total amounts of organic species present in inlet sample. However, there are potential artifacts associated with this sampling method. The removal of the gaseous species in the denuder distorts the gas-particle equilibrium and leads to dissociation of the particulate phase. This phenomenon is particularly true for volatile organic species and lead to significant error in determining gas-to-particle phase partitioning of organic aerosols due to underestimation of the particle phase.
In this study, a theoretical model for simultaneous gas diffusion and aerosol decomposition/evaporation in the parallel plate denuder1 is developed to investigate the effects of denuder sampling artifacts on gas–particle partitioning measurements of semi-volatile organic compounds. We further studied the effect of the denuder design parameters and organic species properties, which may influence the evaporation of the particulate phase. It is observed that the decomposition of pyrene’s (SVOC) particulate phase in the denuder results in the substantial reduction in size of the particles smaller than 0.2 µm and results in the significant error in the phase partitioning measurements of SVOCs.
1. Biswas, P., Lu, C. S., Xu, M., and Pratsinis, S. E., Design equations for gas sampling in diffusion denuders and the effects of particle dissociation, in Visibility and fine particles, C.V. Mathai, Editor. 1990, AWMA Publication. p. 131-145, 1990.