Studies of tropospheric halogen radical chemistry during ozone and mercury depletion events in the Arctic volume I

Chelsea R Stephens, Purdue University

Abstract

The springtime episodic depletion of tropospheric ozone and gaseous elemental mercury in the Arctic has been a focus of intense research over recent years. It has been generally accepted that bromine is the primary driver of Arctic ozone depletion events (ODEs) through a photochemical reaction mechanism catalyzed by Br atoms. Due to the very close correlation between ODEs and atmospheric mercury depletion events (AMDEs) it has been proposed that reactive bromine species (i.e., Br and/or BrO) are the dominant reaction partners for gaseous elemental mercury. The source of the reactive bromine to the Arctic boundary layer is believed to be the saline snow and ice surfaces that are ubiquitous in the Arctic marine environment, however, the specific source and production mechanism of these species remain unknown. Ground-based and satellite observations of BrO in the Arctic have confirmed the presence of reactive bromine chemistry during polar spring. However, there remains significant debate regarding the importance of reactive chlorine on ODEs and AMDEs, as well as on the impact of chlorine on important tropospheric chemical cycles. This gap in our understanding of Arctic chemistry is due in part to a lack of analytical techniques suitable for detecting the very low concentrations of ClO radical species present in the Arctic boundary layer. This work describes a new method developed for the in-situ chemical detection of BrO and ClO radicals in ambient Arctic air using a dynamic chemical reaction system coupled to a gas chromatograph with electron capture detection. This method was used during the Ocean-Atmosphere-Sea Ice-Snowpack (OASIS) 2009 field campaign in Barrow, Alaska for the detection and quantification of ClO radicals. This data, along with the suite of measurements from the OASIS study, was used to analyze the role of reactive chlorine in ODEs and AMDEs by both kinetic analysis and computer model simulations. Additionally, modeling studies were performed to investigate the interactions of the bromine, chlorine, and iodine radical species during ozone depletion periods. Finally, this work discusses the development and testing of a mobile, sled-based version of the chemical reaction method for determining halogen levels directly over the sea ice in an effort to gain a better understanding of the sources of halogen species to the Arctic polar boundary layer.

Degree

Ph.D.

Advisors

Shepson, Purdue University.

Subject Area

Atmospheric Chemistry|Analytical chemistry|Atmospheric sciences

COinS