Reaction of SO(3)with HONO(2)and Implications for Sulfur Partitioningin the Atmosphere

Sulfur trioxide is a critical intermediate for the sulfur cycle and theformation of sulfuric acid in the atmosphere. The traditional view is that sulfurtrioxide is removed by water vapor in the troposphere. However, the concentrationof water vapor decreases significantly with increasing altitude, leading to longeratmospheric lifetimes of sulfur trioxide. Here, we utilize a dual-level strategy thatcombines transition state theory calculated at the W2X//DF-CCSD(T)-F12b/jun '-cc-pVDZ level, with variational transition state theory with small-curvaturetunneling from direct dynamics calculations at the M08-HX/MG3S level. We alsoreport the pressure-dependent rate constants calculated using the system-specificquantum Rice-Ramsperger-Kassel (SS-QRRK) theory. The presentfindingsshow that falloffeffects in the SO3+ HONO2reaction are pronounced below 1 bar. The SO3+ HONO2reaction can be a potentialremoval reaction for SO3in the stratosphere and for HONO2in the troposphere, because the reaction can potentially compete wellwith the SO3+2H2O reaction between 25 and 35 km, as well as the OH + HONO2reaction. The presentfindings also suggest anunexpected new product from the SO3+ HONO2reaction, which, although very short-lived, would have broad implications forunderstanding the partitioning of sulfur in the stratosphere and the potential for the SO3reaction with organic acids to generateorganosulfates without the need for heterogeneous chemistry