Journal of Geophysical Research, Vol. 111, No. D5, D05S03The article of record as published may be located at http://dx.doi.org/10.1029/2005JD006056.In May 2003, the Department of Energy (DOE) Atmospheric Radiation Measurement
(ARM) Program sponsored the Aerosol Intensive Operating Period (AIOP) which was
conducted over the ARM Climate Research Facility (ACRF) in central Oklahoma. One
new instrument that flew in the AIOP, called Cadenza, employed a cavity ring-down
technique to measure extinction coefficient and a reciprocal nephelometer technique to
simultaneously measure scattering coefficient. This instrument is described in this paper,
and measurements are compared to those of conventional instrumentation. Agreement
between Cadenza extinction coefficient and that derived from combining nephelometer
scattering and PSAP absorption (Neph + PSAP) was excellent, about 2%. Agreement
between Cadenza scattering coefficient and TSI nephelometer scattering was also
excellent, about 2%, well within the uncertainty of the nephelometer and Cadenza
scattering measurements. Comparisons between these instruments, made for the special
case of plumes, showed that Cadenza measured extinction and scattering several percent
higher on average than the Neph + PSAP and nephelometer alone. This difference is
likely due to differences in the instrument response time: The response time for Cadenza
is 1 s while that for the nephelometer is a minimum of 8 s. Plumes, identified as
originating from Siberian biomass burning, are characterized. Composite size distributions
from wing-mounted probes showed that two of the plumes had significant large particle
modes that resulted in high values of the effective radius. The effect of the large
particle mode was not seen in the A ° ngstro¨m coefficient calculated from the in-cabin
scattering measurements because of the characteristics of the aircraft inlet
