A prototype instrument for measuring SO2 using laser induced fluorescence

Andrew Rollins (1,2), Troy Thornberry (1,2), Richard McLaughlin (1,2), Laurel Watts (1,2), Steven Ciciora (2), and Ru-Shan Gao (2)

Abstract
Sulfur dioxide is an EPA criteria air pollutant, and a dominant precursor to particulate matter both in the troposphere and in the stratosphere. Intentional releases of SO2 in the stratosphere are being discussed as a potential climate mitigation strategy for the future. Measurements of SO2 at ambient levels are challenging. Commercial fluorescence instrumentation lacks the precision for use in locations other than those that are highly polluted. At the same time, in polluted regions this measurement technique is affected by interferences from nitric oxide and aromatic compounds. Chemical ionization mass spectrometer techniques have been used to measure SO2, but achieving the precision required for background measurements is still challenging. CIMS also has large space/weight/power requirements, and can be subject to complex ionization chemistry and chemical interferences (e.g. H2O). For of these reasons, development of new SO2 instrumentation with high precision and accuracy and capable of being operated on aircraft is desired. We have constructed a custom fiber based tunable UV (217 nm) laser and used it to sensitively detect SO2 using a prototype laser induced fluorescence instrument (LIF). The fiber laser approach has space/weight/power/complexity requirements that are all significant improvements over the previous dye laser approaches to the SO2 LIF measurement technique, and will yield an aircraft deployable instrument. Here we will describe the instrument, and present initial measurement results and plans for aircraft testing.