DOI: 10.25675/10217/194271
title: Dataset associated with "Evaluation of ambient ammonia measurements from a research aircraft using a closed-path QC-TILDAS spectrometer operated with active continuous passivation"

description: Airborne measurements were collected aboard the NSF/NCAR C-130 research aircraft during the Western wildfire Experiment for Cloud chemistry, Aerosol absorption and Nitrogen (WE-CAN) field campaign in summer 2018 and during 16 test-flight hours prior to the WE-CAN deployment. The aircraft conducted seventeen research flights of roughly 6-8 hour duration between 20 July and 31 August in 2018, three test flights of 2-3 hour duration between 21 September and 29 September in 2017, and two test flights on 13 July and 17 July in 2018. Research flights were conducted in the northwestern U.S. with aircraft operations based out of Boise, Idaho; test flights were conducted in the northeastern Colorado Front Range based out of the National Center for Atmospheric Research (NCAR) Research Aviation Facility in Broomfield, Colorado. This repository contains data files associated with ground-based experiments and test/research flights aboard the C-130 aircraft utilized in this analysis. Data files are in ICARTT format (https://www-air.larc.nasa.gov/missions/etc/IcarttDataFormat.htm). File names are formatted as WECAN-NH3_Location_YYYYMMDD_R#, where "location" refers to 1) on the C-130 during a flight day, 2) on the C-130 during a ground day in the hangar at NCAR/RAF, or 3) on the ground in the lab at CSU, "YYYYMMDD" represents the date of collection and R# denotes final data for revision #. Ground-based and test flight data for NH3 include flags for time periods where the instrument was performing a calibration and/or zero. Data is reported at 1 Hz or 10 Hz depending on the experiment performed on that date.
description: A closed-path quantum cascade tunable infrared laser direct absorption spectrometer (QC-TILDAS) was outfitted with an inertial inlet for filter-less separation of particles, a custom-designed aircraft inlet, a custom-built vibration isolation mounting plate, and a custom-built system for optionally adding active continuous passivation for gas-phase measurements of ammonia (NH3) from a research aircraft. The flight-ready instrument was then deployed on the NSF/NCAR C-130 aircraft during research flights and test flights associated with the Western wildfire Experiment for Cloud chemistry, Aerosol absorption and Nitrogen (WE-CAN) field campaign. The flight-ready instrument was configured to measure large, rapid gradients in gas-phase NH3, over a range of altitudes, in smoke (e.g., ash and particles), in the boundary layer (e.g., during turbulence and turns), in clouds, and in a hot aircraft cabin. Important design goals were to minimize motion sensitivity, maintain a reasonable detection limit, and minimize NH3 "stickiness" on sampling surfaces to maintain fast time response in flight. The observations indicate that addition of a high frequency vibration to the laser objective in the QC-TILDAS and mounting the QC-TILDAS on a custom-designed vibration isolation plate were successful in minimizing motion sensitivity of the instrument during flight. Allan variance analyses indicate that the in-flight precision of the flight-ready instrument is 60 ppt at 1 Hz corresponding to a 3-sigma detection limit of 180 ppt. The option for active continuous passivation of the sample flow path with 1H,1H-perfluorooctylamine, a strong perfluorinated base, prevented adsorption of both water and basic species to instrument sampling surfaces. Characterization of the time response in flight and on the ground showed that adding passivant to a "clean" instrument system had little impact on the time response. In contrast, passivant addition greatly improved the time response when sampling surfaces became contaminated prior to a test flight. The observations further show that passivant addition can be a useful tool for maintaining a rapid response for in-situ NH3 measurements over the duration of an airborne field campaign (e.g., ~2 months for WE-CAN test and research flights) since passivant addition also helps to prevent future build-up of water and basic species on instrument sampling surfaces. Therefore, we recommend the use of active continuous passivation with closed-path NH3 instruments when rapid (&gt; 1 Hz) collection of NH3 is important for the scientific objective of a field campaign (e.g., measuring fluxes, sampling from aircraft or another mobile research platform). Passivant addition can be useful for maintaining optimum operation and data collection in NH3-rich/humid environments or when contamination of sampling surfaces is likely, yet frequent cleaning is not possible. Passivant addition may not be necessary for fast operation, even in polluted environments, if sampling surfaces can be cleaned when the time response has degraded.