CARBONAEROSOL

Carbonaceous Aerosol and Radiative Effects Study (CARES)

2 June 2010 - 28 June 2010

Lead Scientist: Rahul Zaveri

Observatory: AAF, MCC

The primary objective of the Carbonaceous Aerosol and Radiative Effects Study (CARES) in 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 (BBA), 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. Light absorption by organic aerosols in the near-UV spectrum was discovered to be a very important part of the radiation budget in a past DOE ASP field campaign, although many questions remain. Several specific science questions under these three topics were addressed during CARES 2010. In addition to obtaining new observation-based understanding from the anticipated field data, the CARES campaign strategy was centered on using the data in various focused model evaluation exercises, so that the resulting new knowledge could be integrated into regional and global climate chemistry models. The sampling strategy during CARES was coordinated, to the extent possible, with CalNex 2010, a major field campaign that was planned in California in 2010 by the California Air Resources Board (CARB), the National Oceanic and Atmospheric Administration (NOAA), and the California Energy Commission (CEC). During summer, the Sacramento urban plume transport is controlled by highly consistent, terrain-driven upslope winds that draw polluted air to the northeast over the oak and pine trees in the Blodgett Forest area by late afternoon. The Sacramento-Blodgett Forest corridor therefore effectively serves as a mesoscale (~100 km) daytime flow reactor in which the urban aerosols undergo significant aging due to coagulation, condensation, and photochemical processes. 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 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 a well-instrumented ground site within the Sacramento urban source area and a downwind receptor site near Cool, CA, to characterize the diurnal evolution of meteorological variables, trace gases/aerosol precursors, and aerosol composition and properties in freshly polluted and aged urban air. As opportunity allowed, one or more NOAA P-3 aircraft flights were carried out in the Sacramento plume in coordination with the G-1 flights to allow wing-tip to wing-tip inter-comparison and provide valuable additional measurements for CARES. The P-3 measurements throughout California provided a regional context for CARES. The resulting datasets lend themselves to focused model evaluation exercises, including local radiative and CCN closures; constrained Lagrangian modeling of SOA formation, aerosol size and composition evolution, and black carbon aging; and 3-D Eulerian modeling of radiative feedback of aerosols on meteorology and regional climate. The second objective during CARES was to take advantage of natural wildfires in the vicinity to study the evolution and properties of biomass burning aerosol. Occurrence of natural wildfires is very likely all over the Central Valley during June/July. Thus, the location and timing of the CARES 2010 campaign allowed us to target such an opportunity when it arose. For more information, see the Overview of the 2010 Carbonaceous Aerosols and Radiative Effects Study (CARES).