Purdue University: Shepson Atmospheric Chemistry Group: Oasis

Oasis 2009

Oasis One

OASIS (Ocean-Atmosphere-Sea Ice-Snowpack) was a large collaborative field campaign aimed at studying the chemical and physical interactions that occur between the atmosphere and cryosphere after polar sunrise.  Scientists from many institutions, including Purdue University, Georgia Institute of Technology, Villanova University, Environment Canada, National Center for Atmospheric Research, Laboratoire de Glaciologie et Geophysique, and the University of Heidelberg, traveled to Barrow, AK, for the two month study.

Atmosphere-cryosphere interactions are complex and have large impacts on the chemistry and composition of the lower troposphere.  The snowpack itself can act as a large photochemical reaction chamber, oxidizing and transforming some chemical species, while producing and emitting others.  Many of these were measured during OASIS, including reactive and molecular halogens, and elemental and reactive mercury, ozone, OH and HOx, NOx, and numerous VOCs.

Halogens are a critical factor in the chemistry of the Arctic troposphere.  Because the water content of the air is so low, OH radicals (primary atmospheric oxidant) are also low, and Cl and Br atoms derived from sea salt become the primary oxidants.  After polar sunrise, photochemically driven reactions involving mostly bromine, initiate so-called “ozone depletion events” (ODEs), the episodic destruction of ground-level ozone from ~40 ppbv to near zero.  Analogous depletions in gaseous elemental mercury are also attributed to this bromine reactivity.  Chlorine is especially important for oxidizing VOCs in this environment and potentially for perpetuating the bromine cycle via production of HOx

One of the roles of the Shepson Group during OASIS was to conduct measurements of BrO and ClO radicals using a flowing chemical reaction method developed in-house (see details here).  Former group members Chelsea Stephens, Phil Tackett, and Adam Keil, set up instrumentation at the KBRW radio tower site, approximately 14 km south of Point Barrow.  The flowtube was housed inside of a heated wooden box mounted to the roof of the building and a heated sample line carried the reaction products inside the building to the GC-ECD.  The measurement system was automated for this field study, allowing continuous sampling through the day and night.

ClO was successfully measured via this method throughout the campaign.  This was the first time that in-situ chemical measurements of this species had ever been achieved.  Peaks up to 12 pptv were measured, with average mixing ratios between 2-4 pptv.  The chemistry at Barrow proved to be highly active in regard to chlorine, which came as a surprise.  Previous estimates of chlorine concentrations given in the literature were very low, and chlorine was believed to be only a minor player in ODE-related chemistry.  One of the major successes of this campaign was that we have first-time measurements of both molecular chlorine (by Georgia Institute of Technology) and chlorine monoxide radicals.  Cl2 concentrations reached as high as 400 pptv!  This has forced us to take a new look at the role of chlorine in Arctic chemistry.

Dr. Paul Shepson

Former Shepson Group member Travis Knepp also participated in the OASIS campaign as a part of the O-Buoy project.  The O-Buoys are a collaborative project between Purdue, the University of Alaska Fairbanks, Bigelow Laboratories, and the US Army Cold Regions Research and Engineering Lab. 

Because the Arctic polar ice cap is a remote and unforgiving environment, constant atmospheric monitoring at manned stations is precluded. As a result, there has been no ground-level data from within the Arctic Basin.  The O-Buoys were designed to be a system of autonomous, ice-tethered buoys that measure ozone, halogens, CO2, and a suite of meteorological parameters.  These data are sent back via iridium satellite.

During OASIS, the first O-Buoy was installed in the sea ice at Elson Lagoon for proof-of-concept testing.  After this successful test, two more buoys were deployed into the Arctic Ocean and one more in the Hudson Bay. 

The O-Buoy project was funded in 2010 to build 12 more buoys through 2015.  The goal is to create an Arctic Ocean wide network to continuously monitor the chemistry and meteorology associated with ODEs.

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