Speaker: Dr. Qianjie Chen
Reporting time: 15:00-16:30, December 30, 2019
Report location: Lecture Hall on the second floor
Inviter: Zhao Yue
The oxidation of dimethyl sulfide (DMS) emitted from the marine biosphere and subsequent formation of sulfur dioxide (SO2), sulfate, and methane sulfonic acid (MSA) are crucial for the formation and evolution of natural aerosols and clouds in the marine troposphere, but are highly simplified in large-scale models of the atmosphere. Reactive halogens, such as bromine oxide (BrO) and hypohalous acids (HOBr and HOCl), play an important role in the sulfur oxidation in the marine troposphere. The reaction of HOBr/HOCl with dissolved SO2 (S(IV)) in clouds also represents a sink of reactive halogens. In this work we investigated the interactions of sulfur and halogen chemistry in the marine troposphere. We measured oxygen isotopes of sulfate collected in the remote marine boundary layer using isotope-ratio mass spectrometry to quantify the contribution of HOBr/HOCl to sulfate aerosol formation. Then the GEOS-Chem global chemical transport model was used to simulate tropospheric sulfur and reactive halogen chemistry. Our laboratory measurements of sulfate oxygen isotopes suggest a large contribution (30-50%) of HOBr/HOCl to sulfate aerosol formation in the marine boundary layer. Implementing the HOBr + S(IV) reaction into the GEOS-Chem model reduces the annual mean tropospheric reactive bromine abundance by 50% globally. With the updated sulfur oxidation scheme, DMS was more efficiently (from 9% to 15%) converted to MSA and less efficiently (from 91% to 75%) converted to SO2 in the marine troposphere, with implications for sulfur aerosol radiative forcing calculations in climate models and using MSA in Antarctic ice cores as a proxy for sea ice extent. I will also briefly describe my recent work on wintertime and Arctic atmospheric chemistry.
Qianjie Chen received a B.Sc. in Atmospheric Sciences from Sun Yat-sen University (2011), a M.Sc. in Meteorology and Physical Oceanography from Utrecht University (2013), and a Ph.D.in Atmospheric Sciences from University of Washington, Seattle (2017), working with Professor Becky Alexander. He is currently a postdoctoral research fellow at University of Michigan, Ann Arbor (since 2018), working with Professor Kerri Pratt. He was the selected participant for the Atmospheric Chemistry Colloquium for Emerging Senior Scientists (ACCESS XV) in 2019. His current research interests include tropospheric sulfur, halogen, and nitrogen chemistry and blowing snow in the polar regions.