See some pictures from our latest field campaign!
Here’s a panorama shot of Fulizi and Victor Nhliziyo (Tuskegee University) from on top of a trailer.
Professor Shepson flying ALAR around the SOAS site. Check out that great new paint job!
Check back soon for more pictures!
Congratulations to recent Purdue graduates Cyrus Baker, Eric Boone, Chase Miller, and Alyssa Hendricks! Cyrus and Eric earned Bachelor’s Degrees in Chemistry, and Chase and Alyssa earned Bachelor’s Degrees in Atmospheric Sciences.
Photochemical production of molecular bromine in Arctic surface snowpacks
Kerri A. Pratt1*, Kyle D. Custard1, Paul B. Shepson1,2, Thomas A. Douglas3, Denis Pöhler4, Stephan General4, Johannes Zielcke4,William R. Simpson5, Ulrich Platt4, David J. Tanner6, L. Gregory Huey6, Mark Carlsen1 and Brian H. Stirm7
Following the springtime polar sunrise, ozone concentrations in the lower troposphere episodically decline to near-zero levels1. These ozone depletion events are initiated by an increase in reactive bromine levels in the atmosphere2-5. Under these conditions, the oxidative capacity of the Arctic troposphere is altered, leading to the removal of numerous transported trace gas pollutants, including mercury6. However, the sources and mechanisms leading to increased atmospheric reactive bromine levels have remained uncertain, limiting simulations of Arctic atmospheric chemistry with the rapidly transforming sea-ice landscape7,8. Here, we examine the potential for molecular bromine production in various samples of saline snow and sea ice, in the presence and absence of sunlight and ozone, in an outdoor snow chamber in Alaska. Molecular bromine was detected only on exposure of surface snow (collected above tundra and first-year sea ice) to sunlight. This suggests that the oxidation of bromide is facilitated by a photochemical mechanism, which was most efficient for more acidic samples characterized by enhanced bromide to chloride ratios. Molecular bromine concentrations increased significantly when the snow was exposed to ozone, consistent with an interstitial air amplification mechanism. Aircraft-based observations confirm that bromine oxide levels were enhanced near the snow surface. We suggest that the photochemical production of molecular bromine in surface snow serves as a major source of reactive bromine, which leads to the episodic depletion of tropospheric ozone in the Arctic springtime.
Read complete article (PDF).
Jon Abbatt
Sea ice and snow help to shape climate at the poles. These surfaces reflect incoming solar radiation, diminishing its ability to warm the planet. Icy surfaces also mediate chemical reactions that affect the composition of the atmosphere1,2. The formation and proliferation of gaseous halogens in polar, snowy environments in spring is one example of such ice-mediated interactions, whereby chemical reactions in the ice facilitate the conversion of halogen-containing compounds to more volatile, reactive species2,3. These halogens — particularly bromine — chew up pollutants such as ozone and mercury, leading to the rapid depletion of tropospheric ozone during polar spring, and the deposition of biologically sensitive mercury to the surface. However, the exact source of these chemically reactive halogens has remained uncertain. Writing in Nature Geoscience, Pratt and colleagues4 show that surface snow can serve as a source of bromine to the Arctic atmosphere.
Read complete article (PDF).
Together with researchers from across the country, the Shepson Group will be participating in the Southern Oxidant and Aerosol Study (SOAS) in Centreville, Alabama from June 1-July 15, 2013. Our goal is to study the interactions of trace gases emitted from forests (biogenic volatile organic compounds, or BVOCs) with urban pollution transported from cities. In the southeastern U.S., the formation of secondary organic aerosol (SOA) formed from the oxidation of BVOCs is known to form a climate-relevant cooling haze (see Goldstein et al. 2009). The Shepson Group is funded by the EPA to study BVOC oxidation, focusing on organic nitrate formation, using a recently-developed (with NSF funding) two-dimensional gas chromatograph (2D-GC), chemical ionization mass spectrometer (CIMS), off-line filter sampling with subsequent electrospray ionization mass spectrometry (ESI-MS) analysis, and box modeling (see Pratt et al. 2012). In addition, the Shepson Group is funded by the NSF for aircraft-based measurements of CO2, CH4, atmospheric turbulence, ozone, particles, and cloud water using the Purdue University Airborne Laboratory for Atmospheric Research (ALAR). Graduate students Kevin McAvey, Fulizi Xiong, Chris Wirth, and Chris Groff are currently preparing for this fantastic campaign!
Photographs of our 2D-GC and CIMS to be deployed to Alabama:
For more information about SOAS, check out:
Collaborators on Shepson SOAS deployment: