Aircraft observations of refractory black carbon during CalNex 2010

Refractory black carbon (rBC) aerosol, resulting from incomplete combustion processes, is a globally important aerosol absorber of solar radiation and a significant component of positive anthropogenic radiative forcing. Measurements of rBC mass concentration were made in California during May and June of 2010 using a Single Particle Soot Photometer (SP2) aboard the NOAA WP-3 aircraft. Observations were made in both the LA Basin and the Central Valley at altitudes ranging from 500-6000ft. These flights provide a unique opportunity to investigate the spatial distribution and impacts of rBC in California. Surface concentrations were typically 50 to several hundred ng/kg and peaked at several thousand ng/kg. A strong correlation (typically r2 >0.8) is observed between rBC and CO and the enhancement ratio is on the low end of those seen in other urban environments. In addition, the dry-particle mass size distributions of rBC are centered at substantially smaller diameters than reported in most previous studies. The implications of these observations for emissions inventories and aerosol radiative forcing are explored.