Abstract
Abstract. Brown carbon (BrC) consists of particulate organic species that preferentially absorb light at visible and ultraviolet wavelengths. Ambient studies show that as a component of aerosol particles, BrC affects photochemical reaction rates and regional to global climate. Some organic chromophores are especially toxic, linking BrC to adverse health effects. The lack of direct measurements of BrC has limited our understanding of its prevalence, sources, evolution, and impacts. We describe the first direct, online measurements of water-soluble BrC on research aircraft by three separate instruments. Each instrument measured light absorption over a broad wavelength range using a liquid waveguide capillary cell (LWCC) and grating spectrometer, with particles collected into water by a particle-into-liquid sampler (CSU PILS-LWCC and NOAA PILS-LWCC) or a mist chamber (MC-LWCC). 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 (3σ) 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 R2=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.
Highlights
1.1 Importance of brown carbonOrganic compounds are a major component of ambient aerosol that affect atmospheric visibility, Earth’s radiation balance and human health
We present a comparison of three WS brown carbon (BrC) measuring systems, including two particle-into-liquid sampler (PILS)-liquid waveguide capillary cell (LWCC) systems and a newly developed mist chamber (MC)-LWCC
The new system was deployed during the NASA FIREX-AQ and contrasted with the performance of the PILS-LWCC systems for measuring water-soluble BrC (WS BrC) on the NSF C-130 aircraft as part of WE-CAN and on the NOAA Twin Otter during FIREX-AQ
Summary
1.1 Importance of brown carbonOrganic compounds are a major component of ambient aerosol that affect atmospheric visibility, Earth’s radiation balance and human health. L. Zeng et al.: Methods for online airborne measurements of BrC ponents are referred to as brown carbon (BrC) because they have a brown or yellow appearance when concentrated, resulting from higher absorption at shorter visible and ultraviolet (UV) wavelengths. Zeng et al.: Methods for online airborne measurements of BrC ponents are referred to as brown carbon (BrC) because they have a brown or yellow appearance when concentrated, resulting from higher absorption at shorter visible and ultraviolet (UV) wavelengths This absorption offsets some portion of the scattering by OA. One can subtract the measured absorption at all wavelengths, including (Abs365 nm) by Abs700 nm (BrC, or corrected Abs365 nm = Abs365 nm − Abs700 nm) This simplified method results in 25 % overestimation of BrC for the MC data compared to estimating the contribution of BC as a function of wavelength (BC AAE = 1). As noted above, the correction would be small (< 5 %)
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