Grant: Research Tools and Instruments - Category 1 (<$150,000)

Fog frequently reduces visibility, causing delays, hazardous conditions and loss of economic activity. Droplets, such as in fog and clouds, form by water condensing on pre-existing particles in the atmosphere. A likely source of these particles in marine and coastal environments is the ocean. Although oceans cover 70% of the earth's surface, current model predictions of their contribution to atmospheric particle mass vary over two orders of magnitude. In addition, recent research has confirmed that a previously unaccounted for organic component is emitted from the ocean into the atmosphere and could be affecting the ability of the particles to act as droplets. Both of these add uncertainty in the contributions of oceans to droplet number and formation, which affect visibility in fogs and reflectivity in clouds. This proposal will employ systematic laboratory experiments to study the effects of water conditions (e.g. temperature and composition) on properties of generated particles. Artificial sea water with varying concentrations of inorganic and organic components will be used to simulate different components of ocean water. Re-creating particles in the laboratory that are representative of real marine particles is a challenge and different generation techniques will be tested. As water conditions and generation techniques are varied, the generated particles will be monitored for their chemical composition, size and hygroscopicity, all of which affect the ability of the particles to turn into droplets. These findings will help us understand how water conditions and processes at the surface determine mass transfer to the atmosphere and ultimately how they affect atmospheric processes such as droplet formation. These results will be applicable to understanding visibility in marine and coastal fogs as well as for cloud droplets, which affect the earth's radiation budget.