Evaluation of inlets used for the airborne measurement of formaldehyde

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The performance of three aircraft inlets used for sampling gas-phase formaldehyde (CH2O) was evaluated. These 1.5 m long inlets were operated with the National Center for Atmospheric Research Tunable Diode Laser Absorption Spectrometer (TOLAS) at flow rates between 7 and 9 standard liters per minute. Laboratory tests were performed on the 1997 North Atlantic Regional Experiment (NARE 97) TOLAS inlet, involving a wide range of sample temperatures (-40° to 25°C), pressures (250-625 torr), relative humidities (≤1 to 85%), and CH2O concentrations (0-25 ppbv). Standard additions on ambient air were performed in the field with another inlet. Sampling artifacts were not observed in either case at CH2O levels less than about 10 ppbv to within the measurement precision (25-120 parts per trillion by volume (1 min, 1σ)) and/or accuracy of standard generation (±6%). Desorption associated with the Herriott Cell was measured under highly polluted conditions, and was largely corrected for by subtracting a frequently acquired instrument background. Inlet shielding and heating minimized error due to liquid water collection. Common inlet materials such as PFA Teflon and silica-coated steel efficiently transmitted CH2O. Copyright 2002 by the American Geophysical Union.

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