Microwave Limb Sounder (MLS) observations of biomass burning products in the stratosphere from Canadian forest fires in August 2017

Abstract

Abstract. Forest fires in British Columbia in August 2017 caused a pyrocumulonimbus event that injected a polluted air mass into the lower stratosphere. The Microwave Limb Sounder (MLS) on the Aura satellite first observed the polluted air mass on 14 August 2017 and continued to observe it for 60 d (100 d in water vapour). We estimate the mass of CO injected into the stratosphere to be 2400 Gg. Events in which a fire injects its burning products directly into the stratosphere 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. The other three events occurred in Australia in December 2006, February 2009 and from December 2019 to January 2020. Unlike the 2006 and 2009 events, but like the 2019–2020 event, the polluted air mass described here had a clearly elevated water vapour content: between 2.5 and 5 times greater than that in the surrounding atmosphere. We describe the evolution of the polluted air mass, showing that it rose to an altitude of about 24 km (31 hPa) and divided into several identifiable parts. In addition to CO and H2O, we observe enhanced amounts of HCN, CH3CN, CH3Cl and CH3OH with mixing ratios in the range to be expected from a variety of measurements in other biomass burning plumes. We use back trajectories and plume-dispersion modelling to demonstrate that the pollutants observed by MLS originated in the British Columbia fires, the likeliest source being at 53.2∘ N, 121.8∘ W at 05:20 UTC on 13 August 2017.

The Hunga Tonga‐Hunga Ha'apai Hydration of the Stratosphere

“…The total injected mass of stratospheric SO 2 (calculated as described by Pumphrey et al. ( 2021 )) was 0.41 ± 0.02 Tg, which pales in comparison to that from previous eruptions measured by MLS, such as the 2008 Kasatochi, the 2009 Sarychev, or the 2019 Raikoke eruptions, which each emitted ∼1 Tg (de Leeuw et al., 2021 ; Pumphrey et al., 2015 ). The mass of SO 2 injected by HT‐HH is even less noteworthy in the context of the 17 Tg injected by the 1991 Pinatubo eruption (Read et al., 1993 ).…”

“…The previous stratospheric H 2 O record measured by MLS was 26.3 ppmv at 100 hPa associated with an overshooting convective event in August 2019 that spanned thousands of square kilometers and persisted for several hours (Werner et al., 2020 ). Two pyroCbs stand out in the MLS H 2 O record: the 2017 Pacific Northwest (Pumphrey et al., 2021 ) and the 2019/2020 Australian New Year's (Kablick et al., 2020 ; Khaykin et al., 2020 ; Schwartz et al., 2020 ) events. Only the Australian pyroCbs injected enough H 2 O to allow an accurate estimate of mass (19 ± 3 Tg).…”

Prolonged and Pervasive Perturbations in the Composition of the Southern Hemisphere Midlatitude Lower Stratosphere From the Australian New Year's Fires

“…The Aura Microwave Limb Sounder (MLS) provides profiles of a suite of atmospheric trace gases, including ozone, water vapor, reservoir and reactive chlorine species, and several markers of biomass burning pollution. Although MLS had observed significant composition anomalies caused by pyroCbs in the upper troposphere and lower stratosphere in the past (e.g., Pumphrey et al., 2011, 2021), the stratospheric impacts of previous events were eclipsed by those from the Australian bush fires of late 2019/early 2020, known as the Australian New Year's pyroCb complex (ANY). MLS measurements were used to track the injection and subsequent ascent of multiple ANY plumes, the most dense of which contained exceptional enhancements in water vapor and biomass–burning products (CO, HCN, CH 3 Cl, CH 3 CN, and CH 3 OH) in the lower and middle stratosphere, accompanied by values of stratospheric species (O 3 and HNO 3 ) more typical of tropospheric air (Kablick et al., 2020; Khaykin et al., 2020; Schwartz et al., 2020).…”

Australian wildfire smoke in the stratosphere: the decay phase in 2020/21 and impact on ozone depletion

“…The PNE smoke was mostly confined between 14 and 20 km height and thus could be removed quite efficiently (from the stratosphere above 13 km). Furthermore, complex horizontal dispersion features in the Northern Hemisphere have been reported in the case of the Canadian smoke event (Kloss et al, 2019;Pumphrey et al, 2021). The smoke became efficiently distributed towards the tropics as well as towards the North Pole within a few weeks.…”