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Gas-Phase Ammonia (NH3)
Gas-Phase Ammonia (NH3)
Aerodyne (model TILDAS-CS) commercial, single-channel, Quantum Cascade Tunable Infrared Laser Direct Absorption Spectrometer (QC-TILDAS) outfitted with a heated inertial inlet for filter-less separation of particles larger than 300 nm and the option for active continuous passivation. The spectrometer is a compact (mini) model with 76 m path length and an infrared laser operating near 967 cm-1. A high sample flow rate (> 10 slpm) improves the instrument's time response by reducing the residence time in the optical cavity and aids in the separation of particles from the sample stream. Active continuous passivation with 1H,1H perfluorocylamine, a strong base that prevents the absorption of water and basic species to the instrument's sampling surfaces, has been shown to improve the instrument's time response to "sticky" molecules (like NH3) on the ground and in flight aboard research aircraft. The instrument can operate on the ground with a 1-Hz precision of 30 pptv (100 pptv detection limit) and in flight with a 1-Hz precision of 66 pptv (200 pptv detection limit). Instrument time response varies with "cleanliness" of the sampling surfaces (sub 1-sec to a few seconds). Passivant addition dramatically improves the time response for dirty or contaminated instrument sampling surfaces, and can prevent the build-up of water and basic species that can slow instrument time response.
Nitrogen Oxides (NO and NO2)
Nitrogen Oxides (NO and NO2)
Ecophysics (model CLD 780 TR) commercial NO analyzer paired with a home-built, inlet-mounted, 395 nm UV-LED converter. NO2 undergoes photolysis to NO in the converter as close as possible to the inlet tip before being detected by the analyzer. The NO analyzer employs the classic NO-O3 chemiluminescence detection technique.
Greenhouse Gas Analyzer (CO, CO2, CH4, H2O)
Greenhouse Gas Analyzer (CO, CO2, CH4, H2O)
The Picarro G2401 commercial greenhouse gas concentration analyzer operates via Cavity Ring-Down Spectroscopy (CRDS). This instrument allows for simultaneous measurements of CO2, CH4, CO with part-per-billion (ppb) sensitivity and negligible drift over months of operation. The Picarro CRDS system combines a 4-species measurement with high precision, ease of field deployability, and long-term reliability. The G2401 is compliant with performance requirements established by The World Meteorological Organization (WMO), and other international networks, such as the Integrated Carbon Observation System (ICOS) for atmospheric monitoring stations.
Peroxyacetyl Nitrates (PANs)
Peroxyacetyl Nitrates (PANs)
One method for measuring PANs is Gas Chromatography with Electron Capture Detection (GC-ECD). The Fischer Group is currently constructing a compact, home-built, GC-ECD instrument for atmospheric measurements of PAN species. The GC-ECD method has the advantage of high sensitivity (~ 1pptv), high specificity, a compact footprint, and the ability to simultaneously measure a suite of PAN species (e.g., MPAN, PPN) on a 5 to 10 minute (or less) timescale.
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