SULFURIC ACID-WATER FORCE FIELD FOR MOLECULAR SIMULATIONS OF ATMOSPHERIC AEROSOLS USING A MIXED QUANTUM/CLASSICAL POTENTIAL

 

Joshua J. McClellan and Thomas Allison

               Computational Chemistry Group/ Chemical and Biochemical Reference Data Division/ Chemical Science and Technology Laboratory, NIST Gaithersburg , MD 20899

 

Sulfuric acid and water play a crucial role in new particle formation in the atmosphere.  By mass, aqueous sulfuric acid is the largest component of particulate matter in the troposphere.  Particulate matter act as cloud condensation nuclei and drive global warming via the albedo effect.  Despite the clear importance of aqueous sulfuric acid formation in the troposphere there are many unknown aspects of its chemistry.  Since the experimental detection limit for tropospheric particulate matter is around 3 nm, the formation mechanism of aqueous sulfuric acid clusters (which cannot be explained by simple classical binary nucleation theory) and the Kelvin effect (how vapor pressure changes with particle size) can be best addressed by the theoretical means presented in this poster.

 

 

Recent theoretical studies of atmospheric nucleation utilize either large-scale classical or small-scale quantum modeling to understand the thermodynamics and kinetics.  A combined approach is preferred for these long time-scale, energetically sensitive phenomena.  Mixed quantum/classical approaches have been widely used in the study of biological systems and a wide range of computer programs and chemical models are readily available.  However, classical force field parameters optimized for biological conditions are not transferable to simulations under atmospheric conditions.  Thus, classical simulations of sulfuric acid and water under atmospherically relevant conditions require new parameters.   Presented here are atomic force field parameters for sulfuric acid and water mixtures under atmospherically relevant conditions.