Preprints
https://doi.org/10.5194/acp-2021-1015
https://doi.org/10.5194/acp-2021-1015

  17 Dec 2021

17 Dec 2021

Review status: this preprint is currently under review for the journal ACP.

Five satellite sensor study of the rapid decline of wildfire smoke in the stratosphere

Bengt G. Martinsson, Johan Friberg, Oscar S. Sandvik, and Moa K. Sporre Bengt G. Martinsson et al.
  • Department of Physics, Lund University, Lund, Sweden

Abstract. Smoke from Western North American wildfires reached the stratosphere in large amounts in August 2017. Limb-oriented satellite-based sensors are commonly used for studies of wildfire aerosol injected into the stratosphere (OMPS-LP (Ozone Mapping and Profiler Suite Limb Profiler) and SAGE III/ISS (Stratospheric Aerosol and Gas Experiment III on the International Space Station)). We find that these methods are inadequate for studies the first 1–2 months after such a strong fire event due to event termination (“saturation”). The nadir-viewing lidar CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) is less affected due to shorter path in the smoke, and, further, provides means that we could use to develop a method to correct for strong attenuation of the signal. After the initial phase, the aerosol optical depth (AOD) from OMPS-LP and CALOP show very good agreement above the 380 K isentrope, whereas the OMPS-LP tends to produce higher AOD than CALIOP in the lowermost stratosphere (LMS), probably due to reduced sensitivity at altitudes below 17 km. Time series from CALIOP of attenuation-corrected stratospheric AOD of wildfire smoke show an exponential decline during the first month after the fire, which coincides with highly significant changes in the wildfire aerosol optical properties. The AOD decline is verified by the evolution of the smoke layer composition, comparing the aerosol scattering ratio (CALIOP) to the water vapor concentration from MLS (Microwave Limb Sounder). Initially the stratospheric wildfire smoke AOD is comparable with the most important volcanic eruptions during the last 25 years. Wildfire aerosol declines much faster, 80–90 % of the AOD is removed with a half-life of approximately 10 days. We hypothesize that this dramatic decline is caused by photolytic loss. This process is rarely observed in the atmosphere. However, in the stratosphere this process can be studied with practically no influence from wet deposition, in contrast to the troposphere where this is the main removal path of sub-micron aerosol particles. Despite the loss, the aerosol particles from wildfire smoke in the stratosphere are relevant for the climate.

Bengt G. Martinsson et al.

Status: open (until 04 Feb 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2021-1015', Hugh C. Pumphrey, 05 Jan 2022 reply
  • CC1: 'Comment on acp-2021-1015', Albert Ansmann, 06 Jan 2022 reply

Bengt G. Martinsson et al.

Bengt G. Martinsson et al.

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Short summary
Large amounts of wildfire smoke reached the stratosphere in 2017. The literature on stratospheric aerosol is mainly based on horizontally viewing sensors that saturates in dense smoke. Using also a vertically viewing sensor with orders of magnitude shorter path in the smoke, we show that the horizontally-viewing sensors misses a dramatic exponential decline of the aerosol load with a half-life of 10 days, where 80–90 % smoke is lost. We attribute the decline to photolytic loss of organic aerosol.
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