Environ. Sci. Technol. 1094, 28, 1307-131 1
Semicontinuous Method for Monitoring SO1 at Low Parts-per-Trillion Concentrations David E. Schorran,' Clarence Fought,t David F. Miller,t William 0. Coulombe, and Robert E. Keislar Desert Research Institute, P.O. Box 60220, Reno, Nevada 89506
Richard Benner University of Alaska, Fairbanks, Alaska 99775-0800
Donald Stedman University of Denver, Denver, Colorado 80208
A technique is described for low parts-per-trillion (ppt) detection of SO2 with high temporal resolution compared to current filter sampling methods. A sulfur chemiluminescence detector, equipped with aquartz burner chamber and a sample probe with a critical orifice, was used as a single detector to analyze SO2 in ambient air by alternately cycling the sample airstream through a SO2 denuder. The method provides one SO2 concentration reading every 10 min. The limits of detection and quantitation were found to be 20 and 70 pptv, respectively. Results from field measurements at a remote site on the south rim of the Grand Canyon during November 1991 are presented, and they indicate a highly variable distribution of SO2 from the limit of detection to near 2 ppbv.
Introduction Sulfur dioxide (SO2)is the key precursor to the formation of sulfate aerosols that cause visibility impairment in the Grand Canyon and other mandatory Class I areas protected by Section 169A of the Federal Clean Air Act. To investigate SO2 sources and transport, it is desirable to monitor SO2 with high sensitivity and high temporal resolution. SO2 concentrations in pristine regions (
