Model simulations of the chemical and aerosol microphysical evolution of the Sarychev Peak 2009 (SO2, HCl, Particles) eruption cloud compared to in situ and satellite observations

International audienceVolcanic eruptions impact climate through the injection of sulfur dioxide (SO2), which is oxidized to form sulfuric acid particles that enhance the stratospheric aerosol optical depth (SAOD). However, uncertainties remain in the atmospheric and climatic impacts due to limitations in model representations of particle microphysics and size, whilst biases have been identified in satellite estimates of post-eruption SAOD. In addition, some eruptions such as Sarychev Peak 2009 co-injected hydrogen chloride (HCl) alongside SO2, whose potential stratospheric chemistry impacts have not been investigated to date. Lurton et al. ACP (2018) present a study of the stratospheric SO2-particle-HCl processing and impacts from the Sarychev Peak eruption, using the CESM1-WACCM-CARMA sectional aerosol microphysics model (with no a priori assumption on particle size). The eruption injected 0.9 Tg of SO2 into the UTLS, enhancing the aerosol load in the Northern Hemisphere. The post-eruption volcanic SO2 is well reproduced by the model compared to IASI satellite data. Co-injection of 27 Gg HCl causes a lengthening of the SO2 lifetime and a slight delay in the formation of aerosols, and acts to enhance the destruction of stratospheric ozone and mono-nitrogen oxides (NOx) compared to the simulation with volcanic SO2 only. We highlight the need to account for volcanic halogen chemistry when simulating the chemistry-climate impacts of eruptions. The model-simulated evolution of effective radius reflects new particle formation followed by particle growth to reach up to 0.2 μm on zonal average. Comparison of the model-simulated particle number and size distributions to balloon-borne in situ stratospheric observations over Kiruna, Sweden (Aug-Sept 2009), and Laramie, USA, (June, Nov, 2009) show good agreement and quantitatively confirm the post-eruption particle enhancement. We show that the model-simulated SAOD is consistent with that derived from OSIRIS when both the saturation bias of OSIRIS and the fact that extinction profiles may terminate well above the tropopause are taken into account. Previous model studies (involving assumptions on particle size) that reported agreement with (biased) post-eruption estimates of SAOD derived from OSIRIS likely underestimated the climate impact of the 2009 Sarychev Peak eruption