| Presentations and Publications
Navea, J., Xu, S., Stanier, C., Young, M., Grassian, V., "Effect of Ozone and Relative Humidity on the Heterogeneous Uptake of
Octamethylcyclotetrasiloxane and Decamethylcyclopentasiloxane on Model Mineral Dust
Aerosol Components", 2009, J. Phys. Chem., Vol 113, Issue 25, pp. 7030-7038.
We have carried out kinetic and reaction yield studies to determine the effect of O3 on the heterogeneous
reaction of two cyclic volatile methylsiloxanes (cVMS), octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane
(D5), with model mineral dust aerosol in order to obtain a better understanding of the
atmospheric fate of cVMS. The heterogeneous chemistry was studied in an environmental reaction chamber
using FT-IR spectroscopy to monitor the reaction progress. The uptake kinetics and the reaction extent for D4
and D5 in the presence of O3 were quantified for two components of mineral dust aerosol, hematite and
kaolinite. Some experiments with a carbonaceous particulate, carbon black, were also performed for D5. The
relative humidity (RH) inside the chamber was varied to investigate the influence of surface adsorbed water
on the heterogeneous chemistry of the dust samples. With the dust samples, but not carbon black, the
coadsorption of O3 introduced a new reaction pathway, characterized by a linear, zero-order, decay of both
gas phase cVMS and ozone. The new pathway does not saturate on the time scale of our experiments. Elevated
RH was observed to decrease the total uptake of cVMS and ozone by the end of the experiment, but the
characteristic linear decay was still present. The atmospheric loss of cVMS due to heterogeneous uptake is
enhanced due to O3, even at higher RH values, but the overall loss rate is reduced at RH values typical of the
troposphere.
|