Atmospheric Sciences Division Seminar

Soot, formed during incomplete combustion, is composed of LAC and organic matter. LAC, also called black carbon (BC), is the dominant absorber of visible solar radiation and plays a major role in climate change as a warming agent second only to CO2 (RC2008). As LAC ages during atmospheric transport, organic and inorganic matter can deposit on these particles; the coating increases the mass absorption cross-section of LAC by as much as 50% (B2006). The mixing state of LAC also determines its atmospheric lifetime as well as its ability to nucleate ice/liquid droplets.

The SP2 is a laser-induced incandescence instrument developed to measure LAC at the single-particle level. The low (<1 fg-LAC) detection limit enables highly time-resolved data collection, as in airborne measurements. The SP2 is also equipped with a scattering detector that allows determination of LAC mixing state. Measurements over Mexico in 2006 (on the NCAR C-130) show a transition from thinly-coated LAC over Mexico City to more thickly-coated LAC after a day of atmospheric transport. Comparison of particulate light absorption measured with a particle soot absorption photometer (PSAP) and the SP2 LAC suggests a LAC absorption cross-section of 12.8 m2/g at 660 nm, apparently unaffected by aging.

The Ice in Clouds Experiment (ICE-L) was conducted over Colorado and Wyoming in November/December 2007. Here, the SP2 was operated downstream of a counterflow virtual impactor (CVI) onboard the NCAR C-130 aircraft, to look at LAC in cloud residual nuclei. Preliminary results from this study will also be presented.