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

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 < 75 ppt or < 0 :075 ppb s(-1) and < 20 ppt in 100s (1 sigma). We demonstrate precisions averaging down to 4 ppt h(-1) (1 sigma 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 18 ppt (22 ppt standard deviation, SD). Enhancement events of EtO lasting a few hours are observed, with peaks as high as 600 ppt. Back-trajectory simulations suggest an EtO source nearly 35 km away. This source along with another are confirmed as emitters through mobile near-source measurements, with downwind concentrations in the 0.5 to 700 ppb range depending on source identity and distance downwind.

Automated summary

We present an Aerodyne tunable infrared laser direct absorption spectrometer with a multipass cell for the detection of ethylene oxide (EtO). The monitor achieves high precisions and demonstrates enhancement events of EtO lasting a few hours with peaks as high as 600 ppt. The source of EtO emission is confirmed through mobile near-source measurements.