An overview of the 2010 Carbonaceous Aerosol and Radiative Effects Study (CARES) field campaign

The primary objective of the Carbonaceous Aerosol and Radiative Effects Study (CARES) in June 2010 was to investigate the evolution of carbonaceous aerosols of different types and their optical and hygroscopic properties in central California, with a focus on the Sacramento urban plume. Carbonaceous aerosol components, which include black carbon (BC), urban primary organic aerosols (POA), biomass burning aerosols, and secondary organic aerosols (SOA) from both urban and biogenic precursors, have been shown to play a major role in the direct and indirect radiative forcing of climate. However, significant knowledge gaps and uncertainties still exist in the process-level understanding of: 1) SOA formation, 2) BC mixing state evolution, and 3) the optical and hygroscopic properties of fresh and aged carbonaceous aerosols. The CARES 2010 field study was designed to address several specific science questions under these three topics.

During summer the Sacramento-Blodgett Forest corridor effectively serves as a mesoscale daytime flow reactor in which the urban aerosols undergo significant aging as they are transported to the northeast by upslope flow. The CARES campaign observation strategy consisted of the DOE G-1 aircraft sampling upwind, within, and outside of the evolving Sacramento urban plume in the morning and again in the afternoon. The G-1 payload consisted of a suite of instruments to measure trace gases, aerosol size distribution, composition, and optical properties. The NASA B-200 aircraft carrying a High Spectral Resolution Lidar (HSRL) and a Research Scanning Polarimeter (RSP) was also deployed to characterize the vertical and horizontal distribution of aerosols and aerosol optical properties. The aircraft measurements were complemented by heavily-instrumented ground sites within the Sacramento urban area and at a downwind site in Cool, California, to characterize the diurnal evolution of meteorological variables, trace gases, aerosol precursors, aerosol size, composition, and optical and Cloud activation properties in freshly polluted and aged urban air. The CARES campaign overlapped with the CalNex 2010 field campaign led by NOAA and CARB.

This paper will present an overview of the campaign, preliminary results, and an outline of various planned model evaluation exercises, which will facilitate the integration of new knowledge and data from the field campaign into regional and global climate-chemistry models.