コーティングされた煤粒子による光吸収の変化を測定することで、地球温暖化効果を確実に予測することができるようになった Measurements of variations in light absorption by coated soot particles lead to a reliable way to predict their global warming effect
2022-07-22 アメリカ・ロスアラモス国立研究所
研究は、黒色炭素が、プルームに存在する凝縮した有機エアロゾルのような他の物質とどのように混合されているかを考えると、煙中の黒色炭素による光の吸収量の観測とモデルによって予測される量の間の長年の食い違い矛盾を解決しています。
山火事が排出するすすや有機粒子は、それぞれ太陽光を吸収したり散乱したりして、混合煙の組成に応じて、大気を暖めたり冷やしたりします。この混合は、大規模火災の煙が地球規模で拡散するにつれて、時間の経過とともに変化します。研究チームは、有機コーティングの成長による経年変化で煤の光吸収効率が増加する系統的な関係を発見しました。
この発見は、現在モデルで近似されている煤の複雑なサイズと構造を正確に捉えている。
＜関連情報＞
- https://discover.lanl.gov/news/0721-wildfire-smoke-observation
- https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022GL099334
山火事の煙がブラックカーボンの光吸収を顕著に、かつ予測可能な形で促進することを示す Wildfire Smoke Demonstrates Significant and Predictable Black Carbon Light Absorption Enhancements
James E. Lee,Kyle Gorkowski,Aaron G. Meyer,Katherine B. Benedict,Allison C. Aiken,Manvendra K. Dubey
Geophysical Research Letters Published: 19 July 2022
DOI:https://doi.org/10.1029/2022GL099334
Abstract
Black carbon (BC) is estimated to have the second largest anthropogenic radiative forcing in earth-systems models (ESMs), but there is significant uncertainty in its impact due to complex mixing with organics. Laboratory-generated particles show that co-mixed non-absorbing material enhances absorption by BC by a factor of 2–3.5 as predicted by optical models. However, weak or no enhancements are often reported for field studies. The cause of lower-than-expected absorption is not well understood and implies a lower radiative impact of BC compared to how many ESMs currently treat aerosols. By analyzing BC aerosol particle-by-particle we reconcile observed and expected absorption for ambient smoke plumes varying in geographic origin, fuel types, burn conditions, atmospheric age and transport. Although particle-by-particle tracking is computationally prohibitive for sophisticated ESMs we show that realistic BC absorption is reliably estimated by bulk properties of the plume providing a suitable parameterization to constrain black carbon radiative forcing.
Key Points
- Ambient smoke plumes exhibited absorption enhancement of black carbon (BC) aerosol, which has not always been reported
- Plume BC absorption enhancement was accurately predicted with a particle-by-particle Mie model suggesting biases in other methods
- Parameterization of plume BC absorption enhancement is developed based on the ratio of coating volume to BC volume concentration
Plain Language Summary
Particles that contain a mix of black carbon and organic aerosol will absorb more light due to the presence of the organics. The increase in absorption due to mixing is uncertain in ambient smoke plumes. In this work, we show that models overestimate black carbon absorption due to particle-to-particle differences in black carbon size and amount of organic coating. When smoke plumes remain in the lower troposphere and don’t experience temperatures below freezing, black carbon absorption can be predicted by an empirical relationship related to the ratio of coating material to black carbon volume in the plume. This simple parameterization is suitable for incorporation into complex earth systems models to for determining the climate impact of black carbon.
