Assessment of online water-soluble brown carbon measuring systems for aircraft sampling

The instruments were deployed on the NSF C-130 aircraft during WE-CAN 2018 as well as the NASA DC-8 and the NOAA Twin Otter aircraft during FIREX-AQ 2019, where they sampled fresh and moderately aged wildfire plumes. Here, we describe the instruments, calibrations, data analysis and corrections for baseline drift and hysteresis. Detection limits (3 sigma) at 365 nm were 1.53 Mm(-1) (MC-LWCC; 2.5 min sampling time), 0.89 Mm(-1) (CSU PILS-LWCC; 30 s sampling time), and 0.03 Mm(-1) (NOAA PILS-LWCC; 30 s sampling time).

Measurement uncertainties were 28 % (MC-LWCC), 12 % (CSU PILS-LWCC), and 11 % (NOAA PILS-LWCC). The MC-LWCC system agreed well with offline measurements from filter samples, with a slope of 0.91 and R-2=0.89. Overall, these instruments provide soluble BrC measurements with specificity and geographical coverage that is unavailable by other methods, but their sensitivity and time resolution can be challenging for aircraft studies where large and rapid changes in BrC concentrations may be encountered.