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Abstract. As wildfires intensify and fire seasons lengthen across the western US, the development of models that can predict smoke plume concentrations and track wildfire-induced air pollution exposures has become critical. Wildfire smoke plume height is a key indicator of the vertical placement of plume mass emitted from wildfire-related aerosol sources in climate and air quality models. With advancements in Earth observation (EO) satellites, spaceborne products for aerosol layer height or plume injection height have recently emerged with increased global-scale spatiotemporal resolution. However, to evaluate column radiative effects and refine satellite algorithms, vertical profiles of regionally representative aerosol properties from wildfires need to be measured directly. In this study, we conducted the first comprehensive evaluation of four passive satellite remote-sensing techniques specifically designed for retrieving plume height. We compared these satellite products with the airborne Wyoming Cloud Lidar (WCL) measurements during the 2018 Biomass Burning Flux Measurements of Trace Gases and Aerosols (BB-FLUX) field campaign in the western US. Two definitions, namely, “plume top” and “extinction-weighted mean plume height”, were used to derive the representative heights of wildfire smoke plumes, based on the WCL-derived vertical aerosol extinction coefficient profiles. Using these two definitions, we performed a comparative analysis of multisource satellite-derived plume height products for wildfire smoke. We provide a discussion related to which satellite product is most appropriate for determining plume height characteristics near a fire event or estimating downwind plume rise equivalent height, under multiple aerosol loadings. Our findings highlight the importance of understanding the sensitivity of different passive remote-sensing techniques on space-based wildfire smoke plume height observations, in order to resolve ambiguity surrounding the concept of “effective smoke plume height”. As additional aerosol-observing satellites are planned in the coming years, our results will inform future remote-sensing missions and EO satellite algorithm development. This bridges the gap between satellite observations and plume rise modeling to further investigate the vertical distribution of wildfire smoke aerosols.
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Rapid evolution of aerosol particles and their optical properties downwind of wildfires in the western US
Abstract. During the first phase of the Biomass Burn Operational Project (BBOP) fieldcampaign, conducted in the Pacific Northwest, the DOE G-1 aircraft was usedto follow the time evolution of wildfire smoke from near the point ofemission to locations 2–3.5 h downwind. In nine flights we maderepeated transects of wildfire plumes at varying downwind distances andcould thereby follow the plume's time evolution. On average there was littlechange in dilution-normalized aerosol mass concentration as a function ofdownwind distance. This consistency hides a dynamic system in which primaryaerosol particles are evaporating and secondary ones condensing. Organicaerosol is oxidized as a result. On all transects more than 90 % ofaerosol is organic. In freshly emitted smoke aerosol, NH4+ isapproximately equivalent to NO3. After 2 h of daytime aging, NH4+ increased and is approximately equivalent tothe sum of Cl, SO42, and NO3. Particle size increased with downwind distance,causing particles to be more efficient scatters. Averaged over nine flights,mass scattering efficiency (MSE) increased in ∼ 2 h by 56 % and doubled in one flight. Mechanisms for redistributing mass from small to large particles are discussed. Coagulation is effective at movingaerosol from the Aitken to accumulation modes but yields only a minor increase in MSE. As absorption remained nearly constant with age, the timeevolution of single scatter albedo was controlled by age-dependentscattering. Near-fire aerosol had a single scatter albedo (SSA) of 0.8–0.9. After 1 to 2 h of aging SSAs were typically 0.9 and greater. Assuming global-average surface and atmospheric conditions, the observedage dependence in SSA would change the direct radiative effect of a wildfire plume from near zero near the fire to a cooling effect downwind.
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- PAR ID:
- 10211174
- Date Published:
- Journal Name:
- Atmospheric Chemistry and Physics
- Volume:
- 20
- Issue:
- 21
- ISSN:
- 1680-7324
- Page Range / eLocation ID:
- 13319 to 13341
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/acp-20-13319-2020
