Showing papers by "James Walega published in 2002"
TL;DR: The optical sensor architecture, performance characteristics of individual pump lasers and DFG, as well as its application to wavelength modulation spectroscopy employing an astigmatic Herriott multi-pass gas absorption cell are described.
Abstract: The development of a compact tunable mid-IR laser system at 3.5 μm for quantitative airborne spectroscopic trace gas absorption measurements is reported. The mid-IR laser system is based on difference frequency generation (DFG) in periodically poled LiNbO3 and utilizes optical fiber amplified near-IR diode and fiber lasers as pump sources operating at 1083 nm and 1562 nm, respectively. This paper describes the optical sensor architecture, performance characteristics of individual pump lasers and DFG, as well as its application to wavelength modulation spectroscopy employing an astigmatic Herriott multi-pass gas absorption cell. This compact system permits detection of formaldehyde with a minimal detectable concentration (1σ replicate precision) of 74 parts-per-trillion by volume (pptv) for 1 min of averaging time and was achieved using calibrated gas standards, zero air background and rapid dual-beam subtraction. This corresponds to a pathlength-normalized replicate fractional absorption sensitivity of 2.5×10-10 cm-1.
150 citations
TL;DR: In situ measurements of NO, NOy, HNO3, ClO, CO2, H2O and particles were made in the plume of an Athena II solid-fuel rocket motor (SRM) with instruments onboard the NASA WB-57F high-altitude aircraft as mentioned in this paper.
Abstract: [1] In situ measurements of NO, NOy, HNO3, ClO, CO2, H2O and particles were made in the plume of an Athena II solid-fuel rocket motor (SRM) with instruments onboard the NASA WB-57F high-altitude aircraft. By normalization to CO2, the NOy emission index was calculated to be 2.7±0.6 g NO2 (kg fuel)−1. HNO3 is a significant and evolving component plume NOy. The principal source of HNO3 is thought to be the heterogeneous reaction between ClONO2 and HCl on emitted alumina particles. These measurements provide the first experimental evidence for the production of HNO3 and the activation of chlorine on SRM-emitted alumina particles in the lower stratosphere.
17 citations
23 Sep 2002
TL;DR: In this article, an airborne tunable diode laser absorption spectrometer has been developed and refined over the past 6 years for such demanding measurements, and the results from a recent study will be presented.
Abstract: Formaldehyde (CH2O) is a ubiquitous component of both the remote atmosphere as well as the polluted urban atmosphere. This important gas-phase intermediate is a primary emission product from hydrocarbon combustion sources as well as from oxidation of natural hydrocarbons emitted by plants and trees. Through its subsequent decomposition, formaldehyde is a source of reactive hydrogen radicals, which control the oxidation capacity of the atmosphere. Because ambient CH2O concentrations attain levels as high as several tens of parts-per-billion (ppbv) in urban areas to levels as low as tens of parts-per-trillion (pptv) in the remote background atmosphere, ambient measurements become quite challenging, particularly on airborne platforms. The present paper discusses an airborne tunable diode laser absorption spectrometer, which has been developed and refined over the past 6 years, for such demanding measurements. The results from a recent study will be presented.
5 citations