David C. Rogers 1, Paul J. DeMott 1, Cindy Twohy 2, Al Cooper 2, Don Hagen 3
Air sample inlets were located on the fuselage. Four different kinds of commercially available CN counters were used. They are all butanol, single particle type instruments.
DC-8 figure and table describing CN instruments
Instrumentation from four investigator groups was used on NASA's DC-8 aircraft during the SUCCESS project April-May 1996 to measure condensation nuclei (CN). These independent CN measurements were in support of other research, and they provided an opportunity for an inter-comparison of this fundamental aerosol quantity.
Time periods were selected from different flights to see how CN measurements compared for a variety of different interesting features. Measurements were made at ambient pressures, or in some cases, boosted above ambient, but for these comparisons, concentrations are expressed at STP (0øC, 1 atm).
Flight data - May 8
4.5 hour flight Kansas to Wisconsin and return
Surface to stratosphere
Clear air and cirrus shield from thunderstorms
All CN showed similar traces, although values occasionally differed by factor of 3 to 100
CN maxima in boundary layer
Stratospheric CN minima (see O3 trace)
Non-volatile CN (stable below 175øC) are about 30% to 90% of total
In cirrus clouds (PVM trace), CN showed greater numbers and more variability than clear air. Since these clouds were debris from thunderstorm anvils, the CN may represent cloud-processed aerosols with boundary layer sources.
Flight data - April 18, T-39 Exhaust Plume
Five minute example from exhaust penetrations.
Exhaust plume structure is echoed in CN and NO traces.
Time offsets are probably due to differences of the time stamp in each data set.
CN measurements differ consistently between these 3 instruments, by factors of 3 to 10.
Ultra-Fine CN shows the highest concentrations, suggesting a predominance of very small particles in fresh aircraft exhaust.
Further analysis of the SUCCESS CN data will also address in-cloud (interstitial) versus out-of-cloud measurements.
Consistently higher concentrations were measured by the Ultra-Fine counters (TSI-3025) and by the TSI-3760.
All CN data showed very strong response in aircraft exhaust plumes. CN peaks were well correlated with NO and other tracers, such as contrail ice particles, although differences in data time stamps produced offsets in the locating the peaks.
CN instruments with the sampling inlet near the trailing edge of the wing (CSU and NCAR) showed a strong impact during rapid aircraft maneuvering. Locations near the aircraft nose and leading edge of the wing were not affected. Inlet placement and design are clearly important factors for aerosol measurement, even for CN, which are dominated by sub-micron particles.