PNNL

Abstract

A new ammonia (NH3) spectrometer was developed based on off-axis integrated cavity output spectroscopy. Its feasibility was demonstrated in airborne test flights in the troposphere on board of the Department of Energy (DOE) Gulfstream-1 (G-1) aircraft. This ammonia gas analyzer consists of an optical cell, a quantum-cascade laser, gas sampling system, electronics for control and data acquisition, and data-analysis software. The NH3 mixing ratio is determined from high-resolution NH3 absorption line shapes by tuning the laser wavelength over the sR(3,K) transition of the fundamental vibration band near 9.67 ?m. Excellent linearity is obtained in a wide range (0- 101 ppb) during calibration. The instrument is capable of collecting data at 2 Hz. Two research flights were conducted over Sunnyside, Washington. In the first test flight, the ammonia gas sensor was used to identify signatures of feedstock from local dairy farms with high vertical spatial resolution under low wind and stable atmospheric conditions. In the second flight, the NH3 spectrometer showed high sensitivity in capturing feedstock emission signals under windy and less stable conditions. Our results demonstrate that this new ammonia spectrometer is airborne feasible and that it has the capability to provide fast in situ observations of ammonia to advance our understanding of atmospheric compositions and aerosol formation.