Supplementary material to "Composition and Reactivity of Volatile Organic Compounds in the South Coast Air Basin and San Joaquin Valley of California"

MethodsThis section presents the details of the measurements used in this study. O3 and NOx measured by chemiluminescenceO3 and NOx were measured by chemiluminescence (CL) (Bourgeois et al., 2022;Bourgeois et al., 2021).Ambient O3 was reacted with pure NO, and the resulting CL signal was detected, amplified, and converted to ambient levels based on ground and in-flight calibrations by standard additions of O3 generated on board the aircraft.Ambient NO was reacted with onboard-generated O3 and the resulting CL signal was converted to ambient levels in a similar method as for O3, but calibrated with standard additions from an NO standard.NO2 was converted to NO by UV photolysis at 385 nm, and detected similarly to NO. O3 , NO, and NO2 were reported at 1-Hz with an uncertainty and precision of ±(2% + 15 pptv), ±(4% + 6 pptv), and ±(7% + 20 pptv) for O3, NO, and NO2, respectively. CO and CH4 measured by laser absorption spectroscopyCO and CH4 were measured using the Differential Absorption Carbon monOxide Measurement DACOM instrument (Sachse et al., 1987).This instrument utilizes three single-mode tunable diode lasers, with CO measured using a quantum cascade laser (QCL) at approximately 4.7 µm and CH4 with an interband cascade laser (ICL) at ~3.3 µm.The DACOM instrument was calibrated, using gases supplied by NOAA ESRL, nominally on a 4-minute clock, but often advanced or delayed in time to avoid calibrating during fire plume encounters.Calibrations provided both slope and intercept values tying signals to species concentrations.Post-campaign analysis of the DACOM CO data indicated that measurement precision (1σ) was approximately 0.1% at 1 Hz and 0.14% at 5 Hz.CO