Stratospheric pollution from Canadian forest fires

Abstract

Abstract. Forest fires in British Columbia in August 2017 caused a pyrocumulonimbus event that injected a polluted airmass into the lower stratosphere. The Microwave Limb Sounder (MLS) on the Aura satellite first observed the polluted airmass on 14 August 2017 and continued to observe it for 60 days (100 days in water vapour). We estimate the mass of CO injected into the stratosphere to be 2–3 Tg. Events such as this are rare: this is the third of four such events in the 16 years since the launch of Aura, the second-largest of the four events, and the only one in the Northern Hemisphere. Unlike the preceding two events, but like the most recent event, the polluted airmass described here had an unusually high water vapour content.

Australian New Year's PyroCb Impact on Stratospheric Composition

“…Stratospheric CO mixing ratios in the BS plume were unprecedented in the first 13 years of the MLS record, exceeding 200 ppbv at 46.4 hPa. The 2017 PNE plume had similar maxima but was observable in MLS data for a much longer period and is estimated to have injected twice as much CO above 215 hPa as did BS (Pumphrey et al, 2020). Using the same approach, we estimate that the total CO injected by ANY is another ∼4× larger than that by the PNE, both above 215 hPa and above 100 hPa, with observed maxima at 46.4 hPa reaching 700 ppbv, against typical background abundances of ∼20 ± 10 ppbv.…”

“…The PNE was a singular occurrence in the first 15+ years of the MLS stratospheric H 2 O record, with 46.4 hPa H 2 O mixing ratios as high as 14 ppmv persisting for over 65 days after the event ( d pne ) (Figure 1u). At 31.6 hPa (not shown), the plume can be tracked with mixing ratios exceeding 6.5 ppmv until ∼105 d pne (Pumphrey et al, 2020). Outliers over 80–105 d pne at 21.5 hPa (Figure 1t) are correlated with the plume, but beyond 100 d pne , they become increasingly difficult to distinguish from the beginnings of seasonally descending high H 2 O anomalies as the plume moves to higher latitudes.…”

“…Resulting long‐lived perturbations of stratospheric composition were observable by satellite‐based atmospheric sensors, including the Aura Microwave Limb Sounder (MLS). The 2009 Australian “Black Saturday” pyroCb event (BS) (Pumphrey et al, 2011), the 2017 Pacific Northwest Event (PNE) (Peterson et al, 2018; Pumphrey et al, 2020), and the 2019–2020 Australian New Years pyroCb complex (ANY) (Kablick et al, 2020, hereinafter K20; Khaykin et al, 2020, hereinafter Kh20) successively rewrote the record books for stratospheric perturbations of biomass burning products and plume ascent rate in the 16‐year MLS data set. The ANY event was an outbreak of at least 18 pyroCbs (K20) at the peak of Australia's historic 2019–2020 “Black Summer” fire season between 29 December 2019 and 4 January 2020 that produced a stratospheric plume with MLS mixing ratios of CO, H 2 O, HCN, CH 3 CN, CH 3 Cl, and CH 3 OH that far exceeded records set by the PNE in the lower‐middle stratosphere.…”

Pollution trace gases C<sub>2</sub>H<sub>6</sub>, C<sub>2</sub>H<sub>2</sub>, HCOOH, and PAN in the North Atlantic UTLS: observations and simulations

“…9l). This potential source region is located well within the Asian summer monsoon pollution pump (Lelieveld et al, 2018;Randel et al, 2010). The trajectory calculations show that the air parcels with enhanced PAN are slowly uplifted by diabatic heating superimposed on the anticyclonic motion within about 40 d, which Vogel et al (2019) referred to as an "upward spiralling range".…”