These data represent continuous measurements of tropospheric nitryl chloride (ClNO2), dinitrogen pentoxide (N2O5), and nitric acid (HNO3) using chemical ionization mass spectrometry, and ozone (O3) using a chemiluminescence O3 monitor. The study was conducted from February 1 to March 10, 2016, at the University of Michigan in Ann Arbor, MI, USA. All measurements were conducted at 12 m above ground level.

CIMS-specific parameters (Mc Namara et al, 2019):- Average CIMS sensitivity to Cl2 (as I(Cl2)- at m/z 197): 3.0 ± 0.4 Hz/ppt (note a)- Relative sensitivity factors used (all relative to I(Cl2)- sensitivity at m/z 197): I(35ClNO2)- (m/z 208): 3.7 ± 0.4 (note b), I(N2O5)- (m/z 235): 0.85 ± 0.08 (note c), I(HNO3)- (m/z 190): 2.3 ± 0.5 (note d)- Detection limits (corresponding to 2 min background periods), campaign average: ClNO2: 0.9 ppt, N2O5: 4 ppt, HNO3: 34 ppt- Sampling line loss correction, to account for wall losses of ClNO2, N2O5, and HNO3 within the sampling line, was applied to the ambient CIMS data as follows: ClNO2: +20%, N2O5: +14%, HNO3: +3%Calibration:- Note a: Cl2 calibrations were performed every 2 h during the campaign by adding Cl2 from a permeation source (VICI Metronics), in N2, to the CIMS inlet air flow. Characterization of the permeation source was completed via the absorption method described by Liao et al (2011). All other species were calibrated offline relative to Cl2 (noted above).- Note b: ClNO2 was synthesized similarly to Thaler et al (2011) and quantified by thermal dissociation to NO2. - Note c: N2O5 was synthesized similarly to Bertram et al (2009) and quantified via measurement of NO2.- Note d: HNO3 was obtained using a permeation source (VICI Metronics) and quantified via measurement of NO3- using ion chromatography (McNamara et al, 2019).Background measurements were performed every 15 min by passing the air flow through a scrubber containing glass wool and stainless steel wool, heated to 120°C (McNamara et al, 2019).