(Color online) Layout of the optical and inlet systems.
Ring-down trace with single exponential fit.
(a) Schematic of the instrument frame and optical table mounted in the P-3 fuselage. (b) Inlet fast flow system and winglet.
Schematic of the sealed, automated filter changer.
Measurement of the wall loss rate (upper trace, solid points) through PFA tubing from exponential fit to the ratio of the concentration measured in two channels against the mean residence time between them. Repeated measurements gave a net loss rate of . The lower trace (open circles) shows the additional loss due to insertion of the machined, PFA pistons that hold the filter in place. The loss rate is similar in this trace, but there is a constant offset indicating a point source loss for in the flow system.
(a) Measurement of the wall loss rate in the heated system at typical flows, converter, and measurement cell temperatures. (b, c) Measurement of the conversion efficiency as a function of heated channel flow rate and preconverter temperature in the field using two different CaRDS instruments sampling from the same manifold. The reference instrument had a flow of and a preconverter temperature of . Variation of the flow and temperature on the second instrument showed that the conversion is not a strong function of the conditions over a flow range of and preconverter temperature of .
Allan variance plots of the instrument baseline in the laboratory (plot A) and from the aircraft during a daylight flight on July 27, 2004 (plot B). The laboratory data have a sensitivity of at but average to a detection limit below at . The aircraft data are considerably noisier, with a sensitivity of and a detection limit at of averaging of .
Results from the test flight of the CaRDS instrument on the NOAA P-3 in March, 2004. Upper left: flight track. Lower: time series of , , and altitude. Upper right: variation of the instrument detection sensitivity (lower axis) and ring-down time constant (top axis) with altitude. The increase in sensitivity due to the increasing ring-down time constant and reduced turbulent flow noise approximately cancels the decrease in ambient number density, leading to a nearly altitude independent sensitivity.
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