This work provides a comprehensive sensitivity calibration of a chemical ionization instrument commonly used in field measurements for the measurement of the toxic isomers methyl isocyanate and hydroxyacetonitrile that are found in the atmosphere. The results from this work have demonstrated that the hydroyacetonitrile isomer was observed in previous field studies rather than the stated identification of methyl isocyanate.

We measured cyanogen bromide (BrCN) in the troposphere for the first time. BrCN is a product of the same active bromine chemistry that destroys ozone and removes mercury in polar surface environments and is a previously unrecognized sink for active Br compounds. BrCN has an apparent lifetime against heterogeneous loss in the range 1–10 d, so it serves as a cumulative marker of Br-radical chemistry. Accounting for BrCN chemistry is an important part of understanding polar Br cycling.

Iodide chemical ionization mass spectrometry (CIMS) is commonly used in atmospheric chemistry laboratory studies and field campaigns. Deployment of the NOAA iodide CIMS instrument in the summer of 2021 indicated a significant and overlooked temperature dependence of the instrument sensitivity. This work explores which analytes are influenced by this phenomena. Additionally, we recommend controls to reduce this effect for future field deployments.