Ozone depletion in the Arctic and Antarctic stratosphere induced by wildfire smoke

Abstract

Abstract. A record-breaking stratospheric ozone loss was observed over the Arctic and Antarctica in 2020. Strong ozone depletion occurred over Antarctica in 2021 as well. The ozone holes developed in smoke-polluted air. In this article, the impact of Siberian and Australian wildfire smoke (dominated by organic aerosol) on the extraordinarily strong ozone reduction is discussed. The study is based on aerosol lidar observations in the North Pole region (October 2019–May 2020) and over Punta Arenas in southern Chile at 53.2∘ S (January 2020–November 2021) as well as on respective NDACC (Network for the Detection of Atmospheric Composition Change) ozone profile observations in the Arctic (Ny-Ålesund) and Antarctica (Neumayer and South Pole stations) in 2020 and 2021. We present a conceptual approach on how the smoke may have influenced the formation of polar stratospheric clouds (PSCs), which are of key importance in the ozone-depleting processes. The main results are as follows: (a) the direct impact of wildfire smoke below the PSC height range (at 10–12 km) on ozone reduction seems to be similar to well-known volcanic sulfate aerosol effects. At heights of 10–12 km, smoke particle surface area (SA) concentrations of 5–7 µm2 cm−3 (Antarctica, spring 2021) and 6–10 µm2 cm−3 (Arctic, spring 2020) were correlated with an ozone reduction in terms of ozone partial pressure of 0.4–1.2 mPa (about 30 % further ozone reduction over Antarctica) and of 2–3.5 mPa (Arctic, 20 %–30 % reduction with respect to the long-term springtime mean). (b) Within the PSC height range, we found indications that smoke was able to slightly increase the PSC particle number and surface area concentration. In particular, a smoke-related additional ozone loss of 1–2 mPa (10 %–20 % contribution to the total ozone loss over Antarctica) was observed in the 14–23 km PSC height range in September–October 2020 and 2021. Smoke particle number concentrations ranged from 10 to 100 cm−3 and were about a factor of 10 (in 2020) and 5 (in 2021) above the stratospheric aerosol background level. Satellite observations indicated an additional mean column ozone loss (deviation from the long-term mean) of 26–30 Dobson units (9 %–10 %, September 2020, 2021) and 52–57 Dobson units (17 %–20 %, October 2020, 2021) in the smoke-polluted latitudinal Antarctic belt from 70–80∘ S.

Comment on ``Stratospheric Aerosol Composition Observed by the Atmospheric Chemistry Experiment Following the 2019 Raikoke Eruption' by Boone et al.

“…According to Ohneiser et al (2021) and Ansmann et al (2022), the contribution of Raikoke sulfate aerosol was of the order of 10-20% to the measured overall aerosol optical thickness (AOT) at 532 nm. Knepp et al (2022) The particles were definitely not larger than expected after moderate volcanic eruptions, at least over the Arctic, and thus not too large for a proper SAGE III aerosol typing as hypothesized by Knepp et al (2022).…”

“…In the same way as we checked the fractional contribution of the Raikoke sulfate aerosol to the observed 532 nm AOT over the polar region (Ohneiser et al, 2021;Ansmann et al, 2022), we analyzed the Raikoke-related AOT fraction by using the 1020 nm extinction profiles measured with a near infrared imager on the ACE satellite and presented by Boone et al (2022). The imager collected four images per second of the Sun.…”

“…As discussed in Ansmann et al (2022), sulfate aerosol originating from the Raikoke volcanic emission of 1.5-1.8 Tg SO 2 (Gorkavyi et al, 2021;Cai et al, 2022) point to maximum AOTs of around 0.025 at 500-550 nm at high northern latitudes in mid-August 2019 and around 0.008 at 1020 nm according to the well accepted relationship between SO 2 mass, sulfate mass (after completing the conversion of SO 2 into sulfuric acid), and the resulting maximum AOT (observable at mid to high northern or southern latitudes).…”

14 years of lidar measurements of polar stratospheric clouds at the French Antarctic station Dumont d'Urville

“…However, some PSC particle formation pathways are still debated (Tritscher et al, 2021) and the adequate model parametrization of PSCs is still challenging. Besides, the recent stratospheric injections of aerosols caused by volcanic eruptions and wildfires also raise questions on the potential interaction with PSC formation processes and subsequent stratospheric ozone depletion (Tencé et al, 2022;Ansmann et al, 2022;Rieger et al, 2021;Stone et al, 2021).…”

Stratospheric chlorine processing after the 2020 Australian wildfires derived from satellite data

“…Model simulations (which assumed wildfire-released aerosols behave like sulfuric acid and water particles) ( 4 ), satellite observations ( 5 – 7 ), and in situ measurements ( 8 ) all found significant ozone decreases in the lower stratosphere at southern hemisphere midlatitudes in 2020 after the wildfire. Unusually low ozone abundances even continued into 2021 ( 6 , 9 ). While there is evidence for some dynamical contributions to the ozone variations observed in that year ( 6 , 10 ), averaged midlatitude values presented in ref.…”