AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Heterogeneous Chemistry of CaCO3 Aerosols with HNO3 and HCl
HAN HUYNH, V. Faye McNeill, Columbia University
Abstract Number: 648 Working Group: Aerosol Chemistry
Abstract Calcite (CaCO3) particles have previously been proposed for use in stratospheric solar radiation management (SRM, Keith et al. PNAS 2016). They also serve as a proxy for calcium-rich mineral dust. We investigated the heterogeneous reactions of submicron CaCO3 particles with HNO3 and HCl in a flow reactor. The particles were aerosolized using dry dispersion and impacted on ZnSe windows, where they were exposed to the reagent gases at stratospherically relevant concentrations, at 296 K and under dry conditions. The chemical composition of the particles was analyzed before and after trace gas exposure using Fourier transform infrared spectroscopy (FTIR). The particle size distribution was characterized prior to deposition using a scanning mobility particle sizer (SMPS) and a micro orifice uniform deposition impactor (MOUDI).
A Ca(OH)(HCO3) termination layer was detected in the form of a HCO3- peak in the FTIR spectra, indicating adsorption of water molecules on the surface. The results demonstrate the reaction of HNO3 with Ca(OH)(HCO3) to produce Ca(NO3) and carbonic acid. HCl reacted with Ca(OH)(HCO3) to produce CaCl2 and carbonic acid. The depletion of the Ca(OH)(HCO3)/Ca(CO3) signal due to reaction with HCl or HNO3 followed pseudo-first order kinetics. Reactive uptake coefficients will be presented and implications for stratospheric ozone in a SRM scenario will be discussed.