Cavity ring-down spectroscopy sensor for detection of hydrogen chloride

C L Hagen,J M Roberts,T C Vandenboer,J L Rath,S S Brown,A P Yalin,B C Lee,I S Franka

doi:10.5194/amt-7-345-2014

Abstract

Abstract. A laser-based cavity ring-down spectroscopy (CRDS) sensor for measurement of hydrogen chloride (HCl) has been developed and characterized. The instrument uses light from a distributed-feedback diode laser at 1742 nm coupled to a high finesse optical cavity to make sensitive and quantifiable concentration measurements of HCl based on optical absorption. The instrument has a (1σ) limit of detection of <20 pptv in 1 min and has high specificity to HCl. The measurement response time to changes in input HCl concentration is <15 s. Validation studies with a previously calibrated permeation tube setup show an accuracy of better than 10%. The CRDS sensor was preliminarily tested in the field with two other HCl instruments (mist chamber and chemical ionization mass spectrometry), all of which were in broad agreement. The mist chamber and CRDS sensors both showed a 400 pptv plume within 50 pptv agreement. The sensor also allows simultaneous sensitive measurements of water and methane, and minimal hardware modification would allow detection of other near-infrared absorbers.

Highlights

1.1 Role of hydrogen chloride (HCl) in the atmosphereChemical reactions involving halogen radical species, such as chlorine and bromine atoms and their oxides, significantly influence the composition of the Earth’s atmosphere
The principal source of HCl in the lower atmosphere is thought to be from acid displacement chemistry on sea spray aerosols in the marine boundary layer, though the extent of the contribution from anthropogenic activity, such as coal burning, is not well understood (McCulloch et al, 1999)
There remains a strong need for improved measurement techniques for HCl, as we address in the present contribution

Summary

Role of HCl in the atmosphere

Chemical reactions involving halogen radical species, such as chlorine and bromine atoms and their oxides, significantly influence the composition of the Earth’s atmosphere. These species play important roles in many atmospheric processes including the formation and destruction of ozone. In polluted marine boundary layers and in populated coastal regions, halogen species can contribute to ozone formation (Tanaka et al, 2000; Knipping and Dabdub, 2003). The principal source of HCl in the lower atmosphere is thought to be from acid displacement chemistry on sea spray aerosols in the marine boundary layer, though the extent of the contribution from anthropogenic activity, such as coal burning, is not well understood (McCulloch et al, 1999).

Methods for HCl detection

Sensor performance

Instrument improvements

Findings

Conclusions