As we have been making our way north, I have been running an aerosol sampler on the top, or the “fly bridge” of the ship. The sampler is basically a pump that pulls air down over a filter, at a rate of roughly 1 cubic meter of air per min (about 40 cubic feet per minute). The sampler is also attached to a wind sensor so that it will only collect air when the wind is coming from the bow sector (or front) of the ship. This way I can avoid contamination from the ship’s diesel engine exhaust which is released toward the stern or back of the ship.
A major goal of mine on this cruise is to collect samples of Saharan dust desert which blows across the Atlantic, most efficiently in the tropics carried from the east by the trade winds. As we move further north we are getting out of the influence of the trade winds and my filters are starting to look different colors! Still south of the influence of the westerly winds from North America, it appears we may now be in an area of relatively pristine marine air, where most of the aerosols are made up of sea salt from waves breaking over the ocean. Toward the end of the cruise, we may potentially see more “gray” filters, indicating aerosols that come from typical “air pollution” sources like burning coal and gas. What color will come up next on my filters?!
–Christopher Hayes (MIT)