Ethylene oxide monitor with part-per-trillion precision for in situ measurements

Abstract

An Aerodyne tunable infrared laser direct absorption spectrometer with a multipass cell with a 413m pathlength for the detection of ethylene oxide (EtO) is presented (TILDAS-FD-EtO). This monitor achieves precisions of <75ppt or <0.075ppbs-1 and <20ppt in 100s (1σ). We demonstrate precisions averaging down to 4ppth-1 (1σ precision) when operated with frequent humidity-matched zeroes. A months-long record of 2022 ambient concentrations at a site in the eastern United States is presented. Average ambient EtO concentration is on the order of 18ppt (22ppt standard deviation, SD). Enhancement events of EtO lasting a few hours are observed, with peaks as high as 600ppt. Back-trajectory simulations suggest an EtO source nearly 35km away. This source along with another are confirmed as emitters through mobile near-source measurements, with downwind concentrations in the 0.5 to 700ppb range depending on source identity and distance downwind.