Modeling study of the impact of SO 2 volcanic passive emissions on the tropospheric sulfur budget

Abstract. The contribution of volcanic emissions is argued as non-linear on the sulfur species burden. Thus, well constraining volcanic emissions inventories is necessary to better study the impacts induced by these pollution sources on the troposheric sulfur composition, as well as on sulfur species concentrations and depositions at the global surface. In this paper, the changes induced by the update of the volcanic sulfur emissions inventory on the global chemistry-transport model MOCAGE (MOdele de Chimie Atmospherique a Grande Echelle) are studied. Unlike the current inventory [Andres and Kasgnoc (1998)], the new inventory [Carn et al. (2016, 2017)] includes contributions from both passive degassing and eruptive emissions with more accu- rate information. Eruptions are provided as daily total amounts of sulfur dioxide (SO2) emitted by volcanoes, while degassing are provided as annual averages with annual uncertainties by volcanoes. Information on plumes altitudes is also available and has been used in the model. The choice is made to look at the year 2013, when a neglieable amount of eruptive volcanic SO2 emissions is referenced, allowing us to focus the study on the impact of passive degassing emissions on the tropospheric sulfur budget. A validation against GOME-2 SO2 total column and MODIS AOD observations shows the improvements of the model results with the new inventory. Because the global volcanic SO2 flux changes from 13 Tg.yr−1 in the current inventory to 23.6 Tg.yr−1 in the new inventory, the updated inventory shows significant differences in the global sulfur budget, mainly in the free troposphere and in the tropics. Even though volcanic SO2 emissions represent 15 % of the total annual sulfur emissions, the volcanic contribution to the tropospheric sulfate aerosol burden is 27 %. Moreover, a sensitivity study on passive degassing emissions, using the annual uncertainties of emissions per volcanoes, also confirmed the non-linear link between tropospheric sulfur species and volcanic emissions. This study highlights the necessity of using accurate estimates of volcanic sources in chemistry-transport models in order to properly simulate tropospheric sulfur species.