Comparison of airborne measurements of NO, NO₂, HONO, NO_<i>y</i>, and CO during FIREX-AQ

Abstract. We present a comparison of fast-response instruments installed onboard the NASA DC-8 aircraft that measured nitrogen oxides (NO and NO2), nitrous acid (HONO), total reactive odd (measured both as (NOy) from sum individually species (ΣNOy)), carbon monoxide (CO) in troposphere during 2019 Fire Influence on Regional to Global Environments Air Quality (FIREX-AQ) campaign. By targeting smoke summertime wildfires, prescribed fires, agricultural burns across continental United States, FIREX-AQ provided unique opportunity investigate measurement accuracy concentrated plumes where hundreds coexist. Here, we compare NO measurements by chemiluminescence (CL) laser-induced fluorescence (LIF); NO2 CL, LIF, cavity-enhanced spectroscopy (CES); HONO CES iodide-adduct chemical ionization mass spectrometry (CIMS); CO tunable diode laser absorption (TDLAS) integrated cavity output (ICOS). Additionally, NOy using CL instrument were compared with ΣNOy (= + nitric (HNO3) acyl peroxy nitrates (APNs) submicrometer particulate nitrate (pNO3)). Other not included they either contributed minimally it (e.g., C1–C5 alkyl nitrates, nitryl chloride (ClNO2), dinitrogen pentoxide (N2O5)) or higher oxidized (NO3), non-acyl peroxynitrates, coarse-mode aerosol nitrate). The intercomparisons demonstrate following points: (1) LIF agreed well within uncertainties but potentially reduced time response for instrument; (2) uncertainties, was average 10 % higher; (3) CIMS highly correlated each fire plume transect, correlation slope vs. all 1 Hz data 1.8, which attribute reduction sensitivity high-temperature environments; (4) budget closure demonstrated flights combined 25 %. However, used fluid dynamic flow model estimate pNO3 sampling fraction through inlet variable one flight another ranged between 0.36 0.99, meaning approximately 0 %–24 may have been unaccounted be due unmeasured such organic nitrates; (5) ICOS TDLAS systematic offset averaged 2.87 ppbv; (6) integrating followed fitting values improved independent measurements.