| Abstract: |
Photochemically-driven formation of new atmospheric particles contributes significantly to the concentrations of cloud condensation nuclei (CCN). Because clouds scatter sunlight back to space, they have a significant effect on the earth’s radiation balance. In fact, in its most recent report, the International Panel on Climate Change (IPCC) identified cloud radiative effects as the largest source of uncertainty in models for climate forcing. Therefore, new particle formation (NPF) needs to be accounted for in global climate models. This project involves experimental research that will lead to microphysical models for the growth rates of newly formed particles. Atmospheric measurements have shown that actual growth rates of freshly nucleated particles are about ten times the values predicted by early models, which account only for sulfuric acid condensation. These fast growth rates are responsible for enabling nucleated particles to reach CCN sizes before they are lost by coagulation with preexisting particles. We built the thermal desorption chemical ionization mass spectrometer (TDCIMS) to measure the composition of these nanoparticles and have found that the high growth rates are largely due to uptake of oxygenated and nitrogen-containing organic compounds, including significant amounts of organic acids and bases (amines). In parallel with our atmospheric observations, we are now carrying out laboratory studies of the thermodynamic properties of such organic compounds so as to fundamentally understand the mechanisms that lead to their uptake by growing nanoparticles. |
