Chlorine activation and enhanced ozone depletion induced by wildfire aerosol

Abstract

Extremes in stratospheric abundances of HCl (record low) 1,2 , ClONO2 2 (record high), and ozone (record low) 1 were observed over southern hemisphere mid-latitudes following the 2020 Australian wildfires by satellite records spanning 15-20 years. These unprecedented changes suggest that wildfire aerosols pose a challenge to stratospheric chlorine and ozone depletion chemistry. Here we propose a wildfire smoke chemical mechanism linking data from the field and the laboratory, and test it by comparison of these extraordinary observations to model simulations. Aged wildfire aerosols likely contain a mix of oxidized organics 3-6 . Laboratory data indicate that HCl is extremely soluble in such species at relatively warm stratospheric temperatures 7-10 in mid-latitudes and Antarctic autumn. We find that the HCl solubility in oxidized organics, and associated enhancements in heterogeneous reaction rates in/on the aerosols, yield remarkable modelled changes in 2020 HCl, ClONO2, and HOCl abundances, in good agreement with observations. Our results indicate that wildfire smoke does not explain the record duration of the 2020 Antarctic ozone hole, but does yield an increase in its area, as well as 3-5% depletion of southern mid-latitude total column ozone. These findings increase concern that more frequent and intense wildfires could delay ozone recovery in a warming world.Massive wildfires in Australia during austral summer of 2019-2020 (December-January) produced pyrocumulonimbus (pyroCb) towers that released about 0.9 Tg of wildfire smoke into the stratosphere 11,12 . Wildfires are also sometimes denoted as bushfires, wildland fires, and forest fires; here we refer to them as wildfires. Wildfire smoke can be expected to be primarily composed of organic material, but its stratospheric chemistry is virtually unknown.Airborne mass spectrometry data 13,14,15 showed that carbonaceous compounds were also frequently present in about 30-40% of individual particles in the background northern hemisphere tropopause and lowermost stratosphere region.The carbonaceous fraction was largely internally mixed with sulfate (i.e., both

The driving effects of common atmospheric molecules for formation of clusters: the case of sulfuric acid, formic acid, hydrochloric acid, ammonia, and dimethylamine

“…For these simulations, the top of the troposphere is dened as 217 K while the bottom of the troposphere is 298 K, and estimates for the monomer concentrations are taken from the literature for 298 K, and reduced by a factor of 1000 at 217 K. We used a water concentration of 7.7 × 10 17 cm −3 at 298 K and 9.9 × 10 14 cm −3 at 217 K, which corresponds to 100% humidity at the bottom and top of the troposphere. 120 Initial monomer concentrations from the literature 22,[120][121][122][123][124][125][126][127][128] at 298 K were reduced by three orders of magnitude at 217 K to compensate for the reduction of CCNforming particles in the upper troposphere. This is a rough estimate based on the three orders of magnitude decrease in concentration of water, and we resort to this approximation since experimental concentrations of these monomers in the upper troposphere are difficult to measure.…”

Summer precipitation and wildfire changes in Siberia induced by stratospheric ozone

“…These wildfires are speeding up permafrost thaw 42 and transforming crctic and boreal lands from carbon sinks to carbon sources 43 , 44 . In addition, wildfire aerosols are causing changes in stratospheric ozone 45 . Central Siberia (100° 130°E and 60° 65°N) is a primary region for summer wildfires (Fig.…”

The Antarctic ozone hole, ultraviolet radiation and bushfires

“…Solomon et al (2023) suggest that the Australian wildfire aerosols could have been responsible for 3-5% of the total ozone depletion at Southern Hemisphere mid-latitudes in 2020; by comparison, recovery of ozone in this region (due to the Montreal Protocol) is on the order of ∼1% per decade. Therefore, these findings increase concerns that wildfires, as well as volcanic eruptions, could delay ozone recovery (Solomon et al 2023). We cannot control volcanoes, and it is possible that the massive Hunga Tonga-Hunga Ha'apai volcanic eruption in 2022 will emerge as a driver of the large 2022 ozone hole (https://atmosphere.copernicus.eu/three-peculiar-antarcticozone-hole-seasons-row-what-we-know#:∼:text=The%20ozone%20depletion%20process%20causing,(PSCs)%20and %20solar%20radiation).…”

“…Research shows that the extensive Australian wildfires injected aerosols into the stratosphere that are capable of depleting ozone (Damany et al 2022; Yook et al 2022) and probably contributed to the larger ozone hole area in 2020 (Fig. 1b; Solomon et al 2023). Unlike the original causes of ozone depletion, which are largely restricted to the coldest polar regions, wildfire smoke could cause the breakdown of ozone across the globe.…”

“…Unlike the original causes of ozone depletion, which are largely restricted to the coldest polar regions, wildfire smoke could cause the breakdown of ozone across the globe. Solomon et al (2023) suggest that the Australian wildfire aerosols could have been responsible for 3–5% of the total ozone depletion at Southern Hemisphere mid-latitudes in 2020; by comparison, recovery of ozone in this region (due to the Montreal Protocol) is on the order of ~1% per decade. Therefore, these findings increase concerns that wildfires, as well as volcanic eruptions, could delay ozone recovery (Solomon et al 2023).…”