RESEARCH ARTICLE


Theoretical Analyses of Aerosol Aging on a Substrate without Wall-Effects by a Cross-Flow



James P. Cowin, 1, Xin Yang, 1, Xiao-Ying Yu*, 2, Martin J. Iedema3
1 Chemical and Materials Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99354, USA
2 Atmospheric Sciences and Global Climate Change Division, Pacific Northwest National Laboratory, Richland, WA 99354, USA
3 Scientific Resources Division, W. R. Wiley Environmental Molecular Science Laboratory, Richland, WA 99354, USA


© 2011 Cowinetet al. ;

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: https://creativecommons.org/licenses/by/4.0/legalcode. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Pacific Northwest National Laboratory, Atmospheric Sciences and Global Change Division, 902 Battelle Boulevard, P.O. Box 999, MSIN K9-30, Richland, WA 99354, USA; Tel: (509)3724524; Fax: (509)3726168; E-mail: xiaoying.yu@pnl.gov
Temporary Address: Cowin In-Situ Science, LLC, Richland, WA 99354, USA
Temporary Address: Fudan University, Shanghai, People’s Republic of China


Abstract

Long time (~1day) aging or reactions of aerosol is typically studied using either large aerosol chambers (>10 m3) or particles supported on a substrate to minimize wall effects. To avoid wall effects in the latter, it is often essential that the wall reactivity be extremely small (<10-5 reactions per encounter) and that the particle loadings be very small (<1 pg/cm2) to eliminate transport-limited trace gas depletion near the particles and substrate. We evaluate here a cross-flow approach, which greatly reduces these constraints. Particles are to be supported on a micromesh (~50% or more open area) through which the reactive gas is drawn at around a few hundred cm/s. The analysis shows how the competitions between flow and diffusion establishes a “zone of isolation” several microns wide around each reactive particle, outside of which the reactivity of other particles or the substrate is irrelevant to the local reactions. This cross-flow approach reduces the effects of substrate and collective particle reactivity typically orders of magnitude, and will facilitate aging studies of supported aerosols.

Keywords:: Aerosol Aging, Transport, Diffusion, Substrate, Wall Effect, Cross-Flow.