Californian Wildfire Smoke Over Europe: A First Example of the Aerosol Observing Capabilities of Aeolus Compared to Ground‐Based Lidar

Abstract

In September 2020, extremely strong wildfires in the western United States of America (i.e., mainly in California) produced large amounts of smoke, which was lifted into the free troposphere. These biomass-burning-aerosol (BBA) layers were transported from the US west coast towards central Europe within 3-4 days turning the sky milky and receiving high media attention. The present study characterises this pronounced smoke plume above Leipzig, Germany, using a ground-based multiwavelength-Raman-polarization lidar and the aerosol/cloud product of ESA's wind lidar mission Aeolus. An exceptional high smoke-AOT > 0.4 was measured, yielding to a mean mass concentration of 8 µg m −3 .The 355 nm lidar ratio was moderate at around 40-50 sr. The Aeolus-derived backscatter, extinction and lidar ratio profiles agree well with the observations of the ground-based lidar PollyXT considering the fact that Aeolus aerosol and cloud products are still preliminary and subject to ongoing algorithm improvements.

Tropospheric and stratospheric wildfire smoke profiling with lidar: mass, surface area, CCN, and INP retrieval

“…Although, recent studies suggest that deposition ice nucleation can be the result of pore condensation freezing, where homogeneous ice nucleation occurs at lower supersaturation in nanometersized pores (David et al, 2019;Marcolli, 2014). When the supercooled smoke particle takes up water or its shell deliquesces, immersion freezing can proceed, where the INP immersed in an aqueous solution can initiate freezing (Knopf et al, 2018;Berkemeier et al, 2014). Finally, if the smoke particle becomes completely liquid (and no insoluble part within the particle is left), homogeneous freezing will take place at temperatures below 235 K (Koop et al, 2000).…”

“…However, in reality, at given air mass lifting conditions, the ice nucleation process can be very complex. The time that solid OM needs for transition to a more liquid state, termed as humidity-induced amorphous deliquescence, can range from several minutes to days at temperatures low enough for ice formation (Mikhailov et al, 2009;Berkemeier et al, 2014;Knopf et al, 2018). Thus the phase change (as function of T and RH) can be longer than typical cloud activation time periods (governed by the updraft velocity), potentially inhibiting full deliquescence and allowing the OA or the organic coating to serve as INP.…”

“…(2) During partial deliquescence, a residual solid core is coated by an aqueous shell, and immersion freezing may proceed. (3) At full deliquescence RH, where the particles are completely liquid (and contain no solid soot fragments), homogeneous freezing will occur at temperatures below about 238 K. (4) The presence of a glassy phase in disequilibrium with surrounding water vapor (e.g., cloud activation at fast updrafts as discussed below) may suppress or initiate ice nucleation beyond the homogeneous ice nucleation limit (Berkemeier et al, 2014;Knopf et al, 2018). A slower updraft velocity allows for more time for deliquescence to proceed, potentially resulting in full deliquescence of the OA particle at warmer and drier conditions compared to when a faster updraft is active.…”

Smoke from 2020 United States wildfires responsible for substantial solar energy forecast errors

“…Particulate matter measurements from ground stations stations in the Western U.S. registered extended exceedances during the 9 d period (figure S3(A)), leading to extreme exposures over Oregon and Washington (figure S3(B)) for several vulnerable populations (supplementary information). The smoke plumes were observed as far away as Leipzig, Germany on 11 September, where co-located ground-based and spaceborne lidars sampled the biomass burning aerosol that were lofted into the free troposphere [5], likely due to intense convection associated with cumulonimbus flammagenitus, or pyrocumulonimbus [21]. Moreover, the High-Resolution Rapid Refresh (HRRR) Smoke modeling system (https://rapidrefresh.noaa.gov/hrrr/HRRRsmoke/) predicted smoke plume transport within the U.S. reasonably well during this period (not shown).…”

Aeolus L2A aerosol optical properties product: standard correct algorithm and Mie correct algorithm

“…The Aeolus optical properties product started to be used in validation studies (e.g. Baars et al, 2021), which showed it could provide valuable data. Finally, assimilation of the Aeolus backscatter coefficient into atmospheric chemistry and transport models is being studied and first results are encouraging (Letertre-Danczak et al, 2021).…”