Friday, September 27, 2019 - 12:00pm to 1:00pm
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100F Pierce Hall, 29 Oxford St., Cambridge

Atmospheric & Environmental Chemistry Seminar

"Cloud and Chemistry Processes Affecting Atmospheric Composition" with Mary C. Barth, National Center for Atmospheric Research.

Clouds cover much of the Earth’s surface at any given time. They are the primary means by which trace gases and aerosols from the boundary layer are lofted to the free troposphere, yet can remove soluble trace gases and aerosols via precipitation. Clouds play an important role on tropospheric composition by altering photolysis rates and supporting oxidation reactions that yield lower volatility products adding to aerosol mass when the cloud drops evaporate. In thunderstorms, lightning generates nitrogen oxides (NOx) promoting the production of ozone in the upper troposphere. This talk will give a summary of findings from the 2012 DC3 (Deep Convective Clouds and Chemistry) field experiment, present some recent analysis of DC3 and SEAC4RS convection, and discuss the acidity of clouds.

Briefly, convective transport and scavenging in regional scale modeling successfully represents observations, however interesting phenomenon such as high methyl hydrogen peroxide scavenging and varying effects of retention of soluble trace gases in ice during cloud drop freezing are still being investigated. Lightning flash rates and lightning-NOx production predictions are still a major uncertainty in regional-scale models due to the complexity of these processes. Up to 20 ppbv ozone was observed to be produced in convective outflows during the course of a day, however stratospheric ozone is also a major contributor to upper troposphere ozone due to the turbulent exchange caused by the thunderstorms.

Cloud water acidity is an important metric for aqueous-phase chemistry, especially of sulfate and organic acid production, yet the cloud water pH is rarely evaluated with observations. Comparisons of a regional model simulation (WRF-Chem) and a global model simulation (CAM-Chem) with observations show reasonable agreement with observations, except near deserts where cloud water pH is often much less acidic than predicted.    

Contact Name: 

Yang Li

Research Areas: 

Harvard University
Center for the Environment

Address: 26 Oxford Street, 4th Floor, Cambridge
Phone: (617) 495-0368

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