Developments in CAPS Extinction-Based Aerosol Measurements
Authors
Andrew Freedman — Aerodyne Research, Inc.
Timothy B Onasch — Aerodyne Research, Inc.
William Brown — Aerodyne Research, Inc.
Frank Hills — Aerodyne Research, Inc.
Fred Bacon — Aerodyne Research, Inc.
Category
Absorbing aerosol
Description
Top: Mass Absorption Coefficient (MAC) at 630 nm calculated from measurements of the absorption cross section of soot produced from an inverted methane diffusion flame versus per particle mass.
Bottom: Same data as above plotted as the per particle absorption cross section versus per particle mass. The slope of the line fit to the data is the derived MAC.
We present a summary of new developments in the use of CAPS optical extinction-based aerosol monitors. We describe a new multi-cell extinction monitor that houses up to 4 measurement cells in a rack-mountable enclosure of only 7U (12.25”) height. This monitor uses less than 75W of electrical power and weighs ~ 30 lbs. All 4 cells can be chosen to measure aerosol extinction at different wavelength (405, 450, 530, 630, 660 and 780 nm available), or as an alternative, one or two cells can be reserved to provide a correction for gas phase absorption in between baselines. We also present results of absorption measurements using the CAPS PMssa monitor. When subtracting scattering from extinction under conditions of low single scattering albedo (SSA<0.2), the PMssa monitor provides a more precise and accurate absorption measurement than can be obtained from a direct absorption measurement. Using the PMssa monitor, the mass absorption coefficient (MAC) of soot produced by an inverted methane flame was determined to be 6.45 ± 0.8 m2 g-1.
