Overview of the CHemistry in the Arctic: Clouds, Halogens, and Aerosols (CHACHA) Campaign Conducted Along the Coastal Alaskan North Slope

From mid-February to mid-April of 2022, the CHACHA teams from five lead universities (Stony Brook U., U. Michigan, Penn State U., U. at Albany, and U. Alaska Fairbanks) and the U. of Wyoming, and a team of other collaborators, conducted 61 aircraft-based research flights over the Chukchi and Beaufort Seas and along the North Slope of Alaska coastal tundra, including over the oil production and processing region of the North Slope of Alaska oil fields. The campaign aimed at producing observational data regarding halogen chemistry in the gas phase, and related particle-phase chemistry, and their connections to clouds in the changing Arctic environment. We flew the U. Wyoming King Air and the Purdue University Airborne Laboratory for Atmospheric Research (ALAR) over snow-covered and newly frozen sea ice, over open leads and polynyas, and over the snow-covered tundra along the North Slope. The King Air was instrumented with a drop-sonde system, aerosol sizing instrumentation, 2D-S and CDP for cloud particle sizing, CIMS for gas-phase halogen measurements, and PILS sampler and DRUM impactor for particle collection for off-line composition analysis, with aerosol instruments alternately sampling behind a CVI inlet when in-cloud or an aerosol inlet when in clear air. ALAR was equipped with an Airborne MAX-DOAS spectrometer for slant-column NO2 and BrO measurements, an LGR in-situ NO2 instrument, and a Picarro CO2/CH4/H2O instrument. Both aircraft were equipped with turbulence probes, and O3 instruments. In this presentation we will summarize and highlight some of the preliminary observations, which include a large number of vertical profiles from the near-surface layer through the top of the boundary layer that enable assessment of and comparison of conditions leading to ozone depletion events (ODEs). We find that stable sunlit boundary layers generally favor ODEs while higher wind speed conditions tend to oppose ODEs. We highlight and compare observations over the frozen ocean, over leads, in-cloud and in clear-air. We also show that leads influenced the formation of warm, moist, and convective boundary layers whose depth reached 400 to 500 m. In contrast, over the ice, statically stable boundary layers prevailed, with temperature inversions often exceeding 14K/km.