Dr. Timothy H. Bertram, Assistant Professor

Dr. Timothy H. Bertram

High sensitivity chemical ionization mass spectrometry for the direct measurement of exchange and reaction at the ocean surface

Dept. of Chemistry and Biochemistry, University of California, San Diego

*The organization and the title are those when awarded


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Chemical reactions at the air-sea interface have been shown to alter oxidant concentrations in the atmosphere.  To date, limitations in trace gas measurement technology have prohibited the direct in situ measurement of air-sea exchange for all but a select number of gases.  Here, we describe the application of high sensitivity chemical ionization mass spectrometry (CIMS) for the selective measurement of trace gas deposition via eddy covariance. We show that eddy covariance techniques, when coupled with high sensitivity CIMS measurements have the sensitivity to directly determine vertical fluxes of reactant and product pairs such as N2O5 and ClNO2[1].  The eddy covariance studies permit a direct assessment of the importance of the air-sea interface as a net source or sink for reactive trace gases in marine environments, while serving to connect mechanistic investigations conducted on the laboratory scale to ambient conditions.

[1] Kim, M., Farmer, D., Bertram, T.H., “A controlling role for the air-sea interface in the chemical processing of reactive nitrogen in the coastal marine boundary layer”, PNAS, 2014.

Research summary

It is very important for the prevention of air pollution to understand the production and reaction mechanisms of various pollutants in the air.

The chemistry at the ocean surface is becoming increasingly important to the overall understanding of our atmosphere. For on-site measurement of trace gases in air, quadrupole mass spectrometers (QMS) which ionize substances and separate them by their mass with AC and DC voltage are commonly used for their measurement. However, conventional QMS instruments lack the required mass resolution and sensitivity to study reaction mechanisms of nitrogen oxides at the ocean surface.

Dr. Bertram has worked on the development of a novel measurement technique for studying the reaction of nitrogen oxides at the sea surface. This system consists of chemical ionization time-of-flight mass spectrometer (CI-TOFMS) which ionize substances by chemical reaction, separates them by their flight time for accurate, fast measurement. Based on direct measurement with the system in the field he has suggested that the ocean surface plays a critical role in nitrogen oxides reactions

This study will enable us to understand the underlying mechanisms of phenomena in the air and lead to much improved understanding and more accurate predictions about the atmospheric environment.