Arctic climate change is resulting in rising temperatures and decreasing sea ice extent. Interactions between sea ice and the atmosphere lead to unique halogen chemistry, resulting in significant losses of atmospheric ozone and mercury. However, significant uncertainty remains in our understanding of the spatial distribution and conditions associated with Arctic ozone depletion events, due to measurement challenges. This research project involves analysis of in-situ ozone and BrO data from long-term O-buoy measurements across the Arctic Ocean, as well as field campaign measurements in Barrow, Alaska. O-buoy data will enable development and evaluation of both simple (zero- and one-dimensional) air-sea ice models, as well as regional atmospheric chemistry models to examine the oxidation pathways in the Arctic. This will improve our ability to predict the impacts of future climate and sea ice changes on the Arctic atmosphere. This integrated understanding is essential to better inform decision-makers about future Arctic system changes. Given the importance of educating the public about science, and climate change in particular, public outreach activities will be integrated into this research in the form of elementary school activities and through the Purdue Climate Change Research Center.
The Arctic is characterized by unique chemical reactions between the air and snow surface. In particular, following springtime polar sunrise, ozone concentrations near the frozen surface decline to near-zero levels. These ozone depletion events are initiated by an increase in reactive bromine levels in the atmosphere. Under these conditions, numerous transported trace gas pollutants, including mercury, are removed from the atmosphere. With the rapid transformation and loss of sea ice in the Arctic, there is an urgent need to understand these chemical interactions and how they impact atmospheric composition to improve models of climate change. This NSF Postdoctoral Fellowship in Polar Regions Research focused on the study of ozone and halogen chemistry through field measurements, snow sampling, and atmospheric modeling. Through analysis of ozone and meteorological data collected on several "O-buoys" across the Arctic Ocean, we gained further information about the durations and characteristics of atmospheric ozone depletion events, unique to the Arctic, which had previously been studied primarily from coastal locations. During the NASA BRomine, Ozone, and Mercury EXperiment (BROMEX), we utilized chemical ionization mass spectrometry to measure the near-surface temporal variability of a variety of species (e.g., Br2, BrO, HOBr, Cl2, ClO, HO2NO2) characterized by unique photochemistry in the Arctic. In addition, outdoor chamber experiments showed that surface snow, collected above both tundra and sea ice, efficiently produced Br2 when exposed to sunlight. Br2 production via the surface snowpack explains observations of BrO enhancements above sea ice, as well as inland tundra, as measured during BROMEX. These findings indicate that atmospherically processed snow is likely a major source of Arctic bromine release, which impacts the distribution and occurrence of ozone depletion events and BrO. Additionally, during BROMEX, size-resolved aerosol number concentrations were measured aboard the Purdue University Airborne Laboratory for Atmospheric Research (ALAR) to examine the role of halogen reactions on aerosol particles. To probe the roles of ozone, bromine, chlorine, and nitrogen chemistry during BROMEX, we are using the one-dimensional model MISTRA with vertical mixing and aerosols described based on profiles measured aboard the Purdue aircraft. In addition, through collaboration with researcher at the University of Washington, we have obtained snow samples from across the Arctic Ocean so that we can measure bulk snow pH and bromide content to predict bromine activation across the Arctic region. Results associated with this postdoctoral fellowship have been published in peer-reviewed literature, including a first-author manuscript in Nature Geoscience. During BROMEX, a class of 3rd graders from the Fred Ipalook Elementary School (Barrow, AK) visited the tundra field site to learn about snow, meteorology, and air sampling. Dr. Pratt was featured on the Climate Central research website (www.climatecentral.org/news/chilling-out-in-alaska-a-scientists-dream-come-true/) during BROMEX. Dr. Pratt also hosted a field campaign blog (http://shepsonbromex.blogspot.com), which has received >13,000 hits; the blog was used for research highlights, elementary and high school student questions, and advertisement of research results to the public after the campaign. Videographers with Green River Pictures created a video about the tundra air sampling, which included an interview with Dr. Pratt (http://vimeo.com/67918840). Associated with this project, Dr. Pratt mentored 2 graduate and 2 undergraduate students (one with the Summer Research Opportunity Program) at Purdue Univ., as well as 2 graduate and 2 undergraduate students (one with the University Research Opportunity Program) at the University of Michigan. Dr. Pratt and her students have presented this work in 10 talks/posters at conferences and 13 university seminars.
