09:55 〜 10:15
[PPS05-09] Experimental Study of SO2 Reactive Uptake in Sulfuric Acid Droplets under Venus-analogous Condition
★Invited Papers
キーワード：金星、硫酸、二酸化硫黄、取り込み、電気力学天秤
Sulfur dioxide (SO2) is the primary sulfur-bearing gas on Venus and plays a pivotal role in its atmospheric chemistry. Observations show that SO2 concentration decreases by three orders of magnitude from the bottom to the top of the cloud layers. However, this SO2 depletion cannot be explained by gas-phase chemistry alone, suggesting a missing SO2 sink within the cloud layers. A potential mechanism for SO2 depletion is the reactive uptake of SO2 by cloud droplets, which is very significant in the Earth’s atmosphere, particularly when oxidants co-exist. However, it is highly uncertain whether the reactive uptake mechanism can substantially deplete SO2 in the cloud layers of Venus because the solubility of SO2 in sulfuric acid (H2SO4) is extremely low. This unaccounted-for pathway necessitates experimental validation under Venus-analogous conditions.
Here, we performed laboratory experiments to examine the uptake of SO2 by H2SO4 droplets of ~10 µm in the presence of nitrogen dioxide (NO2) as an oxidant for SO2 oxidation. A single sulfuric acid droplet was levitated in the electrodynamic balance (EDB) chamber under the ambient temperature (~298 K) and pressure (1 atm). This condition corresponds to an altitude of 50-55 km on Venus.
We find that the size growth of H2SO4 droplets occurs only when both SO2 and NO2 are present, indicating the SO2 oxidation by NO2 in H2SO4 droplets. The growth rate increases with NO2 concentration, and the reactive uptake coefficient of SO2, γSO2, is parameterized by the number density of NO2 (cm-3), nNO2, as log10 γSO2 = 0.572 × log10 nNO2 - 15.03. Numerical simulations suggest that γSO2 = 10-7 is required to reproduce the observed SO2 concentration at the top of the cloud layer. Our results underscore that the reactive uptake of SO2 by H2SO4 droplets may play an important role in SO2 depletion in the cloud layers, warranting future observations of oxidants in the Venusian atmosphere.
Here, we performed laboratory experiments to examine the uptake of SO2 by H2SO4 droplets of ~10 µm in the presence of nitrogen dioxide (NO2) as an oxidant for SO2 oxidation. A single sulfuric acid droplet was levitated in the electrodynamic balance (EDB) chamber under the ambient temperature (~298 K) and pressure (1 atm). This condition corresponds to an altitude of 50-55 km on Venus.
We find that the size growth of H2SO4 droplets occurs only when both SO2 and NO2 are present, indicating the SO2 oxidation by NO2 in H2SO4 droplets. The growth rate increases with NO2 concentration, and the reactive uptake coefficient of SO2, γSO2, is parameterized by the number density of NO2 (cm-3), nNO2, as log10 γSO2 = 0.572 × log10 nNO2 - 15.03. Numerical simulations suggest that γSO2 = 10-7 is required to reproduce the observed SO2 concentration at the top of the cloud layer. Our results underscore that the reactive uptake of SO2 by H2SO4 droplets may play an important role in SO2 depletion in the cloud layers, warranting future observations of oxidants in the Venusian atmosphere.