Wildfire smoke in the lower stratosphere identified by in situ CO observations
<p>Wildfires emit large quantities of aerosols and trace gases, which occasionally reach the lower stratosphere. In August 2017, several pyro-cumulonimbus events injected a large amount of smoke into the stratosphere, observed by lidar and satellites. Satellite observations are in general the...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-11-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/20/13985/2020/acp-20-13985-2020.pdf |
| Summary: | <p>Wildfires emit large quantities of aerosols and trace gases, which occasionally reach the lower stratosphere. In August 2017, several pyro-cumulonimbus events injected a large amount of smoke into the stratosphere, observed by lidar and satellites. Satellite observations are in general the main method of detecting these events since in situ aircraft- or balloon-based measurements of atmospheric composition at higher altitudes are not made frequently enough. This work presents accidental balloon-borne trace gas observations of wildfire smoke in the lower stratosphere, identified by enhanced <span class="inline-formula">CO</span> mole fractions at approximately 13.6 <span class="inline-formula">km</span>. In addition to <span class="inline-formula">CO</span> mole fractions, <span class="inline-formula">CO<sub>2</sub></span> mole fractions and isotopic composition of <span class="inline-formula">CO</span> (<span class="inline-formula"><i>δ</i><sup>13</sup></span>C and <span class="inline-formula"><i>δ</i><sup>18</sup></span>O) have been measured in air samples, from both the wildfire plume and background, collected using an AirCore and a lightweight stratospheric air sampler (LISA) flown on a weather balloon from Sodankylä (4–7 September 2017; 67.37<span class="inline-formula"><sup>∘</sup></span> N, 26.63<span class="inline-formula"><sup>∘</sup></span> E; 179 m a.m.s.l.), Finland. The greenhouse gas enhancement ratio (<span class="inline-formula">ΔCO:ΔCO<sub>2</sub></span>) and the isotopic signature based on <span class="inline-formula"><i>δ</i><sup>13</sup>C(CO)</span> and <span class="inline-formula"><i>δ</i><sup>18</sup>O(CO)</span> independently identify wildfire emissions as the source of the stratospheric <span class="inline-formula">CO</span> enhancement. Back-trajectory analysis was performed with the Chemical Lagrangian Model of the Stratosphere (CLaMS), tracing the smoke's origin to wildfires in British Columbia with an injection date of 12 August 2017. The trajectories are corrected for vertical displacement due to heating of the wildfire aerosols, by observations made by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument. Knowledge of the age of the smoke allowed for a correction of the enhancement ratio, <span class="inline-formula">ΔCO:ΔCO<sub>2</sub></span>, for the chemical removal of <span class="inline-formula">CO</span> by <span class="inline-formula">OH</span>. The stable isotope observations were used to estimate the amount of tropospheric air in the plume at the time of observation to be about <span class="inline-formula">45±21</span> <span class="inline-formula">%</span>. Finally, the plume extended over 1 km in altitude, as inferred from the observations.</p> |
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| ISSN: | 1680-7316 1680-7324 |