Subminute measurements of SO2 at low parts per trillion by volume mixing ratios in the atmosphere

The continuous sulfur dioxide detector (CSD) is a sensitive instrument for reliable measurements at high time resolution in the atmosphere. This new i nstrument is based on a SO2, measurement technique utilizing the sulfur che miluminescence detector, previously validated in a rigorously blind experim ent sponsored by the National Science Foundation. Simplified sample handlin g, denuder separation technology, and the intrinsic sensitivity and fast re sponse of the detector permit measurement at levels below 100 parts per tri llion by volume in tens of seconds with the CSD. The CSD provides a differe ntial measurement where response from ambient SO2 is determined by the diff erence between air containing SO2 and air scrubbed Of SO2, where both air s amples contain other detectable sulfur species. Digital signal post process ing with phase-locked amplification of the detector signal enhances the pre cision and temporal resolution of the CSD. Oversampling of the detector sig nal at 10 Hz permits subsequent data retrieval to be adapted to changing am bient levels by either enhancing signal to noise when sulfur dioxide levels are low or by maximizing temporal resolution of derived data when levels a re high. The instrument has advantages over existing instruments based on c hromatographic separation in that the CSD provides accurate and reliable me asurements at low parts per trillion by volume sulfur dioxide with high tim e resolution. The CSD is compact and automated and does not require cryogen ic materials, making this instrument suitable for remote field locations. T he high temporal resolution, specificity for SO2, and sensitivity of the CS D make it a good candidate for installation on an aircraft. Airborne studie s Of SO2 with a sensitive, fast time response instrument may offer new insi ght into the understanding of phenomena such as gas-to-particle conversion, long-range transport of pollutants, and the oxidation of biogenically prod uced sulfur gases.