Examination of brown carbon absorption from wildfires in the western US during the WE-CAN study

Abstract

Abstract. Light absorbing organic carbon, or brown carbon (BrC), can be a significant contributor to the visible light absorption budget. However, the sources of BrC and the contributions of BrC to light absorption are not well understood. Biomass burning is thought to be a major source of BrC. Therefore, as part of the WE-CAN (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen) study, BrC absorption data were collected on board the National Science Foundation/National Center for Atmospheric Research (NSF/NCAR) C-130 aircraft as it intercepted smoke from wildfires in the western US in July–August 2018. BrC absorption measurements were obtained in near real-time using two techniques. The first coupled a particle-into-liquid sampler (PILS) with a liquid waveguide capillary cell and a total organic carbon analyzer for measurements of water-soluble BrC absorption and WSOC (water-soluble organic carbon). The second employed a custom-built photoacoustic aerosol absorption spectrometer (PAS) to measure total absorption at 405 and 660 nm. The PAS BrC absorption at 405 nm (PAS total Abs 405 BrC) was calculated by assuming the absorption determined by the PAS at 660 nm was equivalent to the black carbon (BC) absorption and the BC aerosol absorption Ångström exponent was 1. Data from the PILS and PAS were combined to investigate the water-soluble vs. total BrC absorption at 405 nm in the various wildfire plumes sampled during WE-CAN. WSOC, PILS water-soluble Abs 405, and PAS total Abs 405 tracked each other in and out of the smoke plumes. BrC absorption was correlated with WSOC (R2 value for PAS =0.42 and PILS =0.60) and CO (carbon monoxide) (R2 value for PAS =0.76 and PILS =0.55) for all wildfires sampled. The PILS water-soluble Abs 405 was corrected for the non-water-soluble fraction of the aerosol using the calculated UHSAS (ultra-high-sensitivity aerosol spectrometer) aerosol mass. The corrected PILS water-soluble Abs 405 showed good closure with the PAS total Abs 405 BrC with a factor of ∼1.5 to 2 difference. This difference was explained by particle vs. bulk solution absorption measured by the PAS vs. PILS, respectively, and confirmed by Mie theory calculations. During WE-CAN, ∼ 45 % (ranging from 31 % to 65 %) of the BrC absorption was observed to be due to water-soluble species. The ratio of BrC absorption to WSOC or ΔCO showed no clear dependence on fire dynamics or the time since emission over 9 h.

Brown carbon absorptivity in fresh wildfire smoke: associations with volatility and chemical compound groups

“…75 Numerous previous studies have observed correlations between levoglucosan and BrC from biomass combustion. [76][77][78] A growing number of studies show that levoglucosan may not be stable in the atmosphere for long periods of time [79][80][81] which further suggests that we sampled BB plumes that had undergone minimal atmospheric processing. The quan-tied terpene concentrations were comparable to the sugar concentrations and were likely formed from heat-induced volatilization of unburnt biomass in the wildres.…”

Summertime Airborne Measurements of Ammonia Emissions From Cattle Feedlots and Dairies in Northeastern Colorado

“…The liquid sample from the PILS was sent to a Brechtel Fraction Collector to collect samples for offline analysis (Sorooshian et al., 2006). The PILS liquid flowrates were set and the fraction collector operated similarly to the approach used during WE‐CAN (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen) to obtain ∼1.2 mL of liquid sample every 2 min (Sullivan et al., 2022). Pre‐loaded carousels were manually switched during flight.…”

Relative Humidity Modulates the Physicochemical Processing of Secondary Brown Carbon Formation from Nighttime Oxidation of Furan and Pyrrole

“…On the other hand, higher RH decreased the MAC of secondary BrC derived from α-pinene, suggesting that the effect of RH on MAC may differ depending on the type of VOCs. It is noted that a rise in RH may result in increased liquid water content in wildfire aerosols, where water-soluble organics can contribute to a large portion (e.g., ∼45% at 405 nm) of BrC light absorption . Despite the extensive investigations, the effect of RH on secondary BrC formation remains inconclusive.…”