Abstract

Sulfur dioxide (SO2) is an important precursor for formation of atmospheric sulfate aerosol and acid rain. We present an instrument using Broad Band Cavity Enhanced Absorption Spectroscopy (BBCEAS) for the measurement of SO2 with a minimum limit of detection of 0.6 ppbv using the spectral range 305.5–312 nm and an averaging time of 60 seconds. The instrument consists of high reflectivity mirrors (0.9984 at 310 nm) and a deep UV light source. The effective absorption path length of the instrument is 610 m in a 0.957 m base length. Published reference absorption cross-sections were used to fit and retrieve the SO2 concentrations and were compared to a diluted standard for SO2. The comparison was well correlated, R2 = 0.9985 with a correlation slope of 1.01.

Highlights

  • Sulfur dioxide (SO2) is a precursor to formation of atmospheric sulfate aerosol and acid rain (Schwartz, 1987)

  • We present an instrument using Broad Band Cavity Enhanced Absorption Spectroscopy (BBCEAS) for the measurement of SO2 with a minimum limit of detection of 0.6 ppbv using the spectral range 305.5 – 312 nm and an averaging time of 60 seconds

  • 20 There are several well-established measurement techniques for SO2 that have been used in routine air quality monitoring for decades including UV fluorescence (Parrish and Fehsenfeld, 2000) and the pararosaniline wet chemistry technique (West and Gaeke, 1956) which are the two Environmental Protection Agency (EPA) Federal Reference and Equivalent Methods (Gilliam and Hall, 2016)

Read more

Summary

Introduction

Sulfur dioxide (SO2) is a precursor to formation of atmospheric sulfate aerosol and acid rain (Schwartz, 1987). Broad Band Cavity Enhanced Spectroscopy (BBCEAS) leverages a high finesse optical cavity of a given wavelength to realize long path lengths, similar to LP- and MAX-DOAS but with in situ sampling. The measured concentrations were retrieved by non-linear least squares fitting of the cavity extinction as given by Fiedler et al (2003) and Washenfelder et al (2008):. The concentrations of the trace gases of interest was retrieved by non-linear least square fitting in IGOR (Wavemetrics) by minimizing the error of the following equation with a 3rd degree polynomial enabling a Differential Optical Absorption Spectroscopy retrieval (Platt and Stutz, 2008):. Because of the fitted polynomial, the retrieval is only sensitive to the structured (differential) cross-section and is insensitive to broad changes in the light source shape, 100 aerosol scatter (if no filter was used) and other broad-band absorbers (many organic compounds that interfere with fluorescence measurements). Fitting was carried out from 305.5 – 312 nm with a 3rd order polynomial and the retrieved concentration was converted to mixing ratio using the measured temperature and pressure

Comparison to SO2 standard
Noise Evaluation
Conclusions

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.