Title: Representing effects of aqueous phase reactions in shallow cumuli in global models

Abstract

Aqueous phase reactions are important, sometimes dominant (e.g., for SO₂), pathways for the oxidation of air pollutants at the local and/or global scale. In many current chemical transport models (CTMs), the transport and aqueous reactions of chemical species are treated as split processes, and the subgrid-scale heterogeneity between cloudy and environmental air is not considered. Here using large eddy simulation (LES) with idealized aqueous reactions mimicking the oxidation of surface-originated SO₂ by H₂O₂ in shallow cumuli, we show that the eddy diffusivity mass flux (EDMF) approach with a bulk plume can represent those processes quite well when entrainment/detrainment rates and eddy diffusivity are diagnosed using a conservative thermodynamic variable such as total water content. The reason is that a typical aqueous reaction such as SO₂ aqueous oxidation is relatively slow compared to the in-cloud residence time of air parcels in shallow cumuli. As a result, the surface-originated SO₂ is well correlated with and behaves like conservative thermodynamic variables that also have sources at the surface. Experiments with various reaction rate constants and relative abundances of SO₂ and H₂O₂ indicate that when the reaction timescale approaches the in-cloud residence time of air parcels, the errors of the bulk plume approach startmore » to increase. Finally, treating chemical tracer transport and aqueous reaction as split processes leads to significant errors, especially when the reaction is fast compared to the in-cloud residence time. Overall, the EDMF approach shows large improvement over the CTM-like treatments in matching the LES results.« less

Authors:

Nie, Ji ^[1]; Kuang, Zhiming ^[2]; Jacob, Daniel J. ^[3]; Guo, Jiahua ^[3]

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+ Show Author Affiliations

1. Columbia Univ., New York, NY (United States). Lamont-Doherty Earth Observatory
2. Harvard Univ., Cambridge, MA (United States). Dept. of Earth and Planetary Sciences and John A. Paulson School of Engineering and Applied Sciences
3. Harvard Univ., Cambridge, MA (United States). John A. Paulson School of Engineering and Applied Sciences

Publication Date:

Tue May 17 00:00:00 EDT 2016

Research Org.:

Harvard Univ., Cambridge, MA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER)

OSTI Identifier:

1469111

Grant/Contract Number:  

SC0008679

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research: Atmospheres

Additional Journal Information:

Journal Volume: 121; Journal Issue: 10; Journal ID: ISSN 2169-897X

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES