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SUMMARY: Stratospheric Heterogeneous Chemistry after the 2019–2020 Austr
 alian Wildfires - Dr.  Kane Stone\,  Research Scientist\, Department of Ea
 rth Atmospheric and Planetary Sciences\, Massachusetts Institute of Techno
 logy
DTSTART:20241105T150000Z
DTEND:20241105T160000Z
UID:TALK222400@talks.cam.ac.uk
CONTACT:Dr Megan Brown
DESCRIPTION:The 2019–2020 Australian wildfires injected an estimated 1 T
 g of smoke into the Southern Hemisphere stratosphere\, significantly incre
 asing aerosol surface area for heterogeneous chemistry to occur. Unlike a 
 volcanic eruption which typically only enhances N2O5 hydrolysis in the mid
 latitudes\, the Australian wildfires also caused large perturbations in ch
 lorine containing species. Large decreases of HCl\, large increases in ClO
 NO2\, and enhanced activated chlorine were observed in both the Southern H
 emisphere midlatitude and polar regions. This is indicative of HCl based h
 eterogeneous chemistry occurring at a faster rate. Previous work has shown
  that heightened HCl solubility in aerosols with elevated organic content 
 is a likely driver of the enhanced heterogeneous chemistry. In this semina
 r\, we will discuss how we modelled this enhanced heterogeneous chemistry 
 in CESM-CARMA for both 2020\, when very large amounts of wildfire organics
  are present\, and 2021\, when most of the wildfire aerosols have been rem
 oved from the stratosphere. A clear seasonality in the perturbations of ch
 lorine species and ozone is observed. This seasonality is captured very we
 ll in our model simulations and is photochemically driven. Similarly to th
 e midlatitudes\, very unusual perturbations in HCl and ClONO2 occurred in 
 the Antarctic polar region in both 2020 and 2021 before the polar night. F
 or a normal year without wildfire smoke\, models cannot adequately replica
 te the observed rapid HCl decline that occurs in early austral winter. The
  current cause of this is unknown. However\, in both 2020 and 2021\, total
  HCl loss occurred months earlier than normal due the presence of wildfire
  organic aerosols. Our model simulations replicated the early onset of HCl
  loss seen in the observations very well. In addition to wildfire organics
 \, the lower stratosphere typically has a large amount of “background”
  organics originating from non-pyrocumulonimbus biomass burning. Both the 
 background and Australian wildfire aerosols are expected to be in mixed ae
 rosol with sulfate. Based on our model simulations\, the expected phases o
 f organic-nonorganic mixtures will be discussed\, including any potential 
 differences between the background and Australian wildfire organics. Final
 ly\, we will discuss how unique we think the 2019–2020 Australian wildfi
 re event was regarding both its effects on stratospheric chemistry and its
  size in comparison to other past pyroCB injections of wildfire smoke and 
 what this could mean for the future.\n\n\nJoin Zoom Meeting\nhttps://us02w
 eb.zoom.us/j/88001984520?pwd=g6lFa4Z4Lh7iBh57SY7UF1wfbn1QNS.1
LOCATION:Chemistry Dept\, Unilever Lecture Theatre and Zoom
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