The primary activity of this project was making the first measurements of aerosol particle size, composition and number at high time resolution in Coastal Antarctica.   The research team deployed a package of cutting-edge scientific instrumentation, including an aerosol mass spectrometer to measure the chemical make up of tiny particles in Antarctica, laser aerosol sizing instrumentation measure the number of particles from 10x smaller 30 times larger than the width of your hair. Other instruments to measure the concentration of gases and weather measurements were also taken.  So that we didn?t measure pollution from the McMurdo Station where we lived during this project, all of these instruments were dragged in a trailer on skis 30 km (about 20 miles) by a bulldozer to sea ice between McMurdo Station and the ocean.   Measurements were made for two months during the summer season when there is sunlight all day and relatively calm weather and two months during the following spring season, when the sun is rising and windy and cold weather prevails.   

McMurdo was one of the cleanest places measurements such as this have been made.  We found that the aerosol particles we measured two seasons showed significant differences in abundance and composition between the seasons.  More importantly we saw large changes in aerosol particle composition on a daily and even hourly basis within each season. The hourly to daily variability has not been previously measured, as prior measurements of aerosol composition were made by collecting aerosol on filters for later analysis with a time resolution from days to weeks.   These high time resolution measurements confirmed several phenomena observed in prior measurements ? the air in Antarctic at the ground has a very low aerosol concentration relative to the mid-latitudes where many people live, the majority of larger aerosol particles (with diameters greater than 0.5 micrometers or about half the width of your hair) are derived from sea-salt and there are more aerosol in the spring than summer.    During the summer time there is a second type of smaller aerosol (diameters around 0.25 micron and smaller) that has a different chemical composition with high concentrations of sulfate.  This separate type of aerosol particle likely originates from biological activity in the ocean when the sun is shining and the waters are warmer.  These small aerosols are almost always present without the variability seen in the larger sea-salt particles. 

These high time resolution measurements also revealed several new discoveries that have not been seen before by previous measurements.    On the snow-covered sea ice where these measurements were taken, high wind speeds had a much bigger impact on the number of aerosol particles and the chemical composition of that aerosol than where the air that was sampled had come from. Under higher wind speeds (above 15 mph), we observed a significant increase in the number of aerosol particles and linked that to blowing snow conditions, which was independent of where the air was coming from.  These increase in aerosol particles was not due to the snow itself, which the instruments do not measure, but to aerosol particles mixed with the snow.    These aerosol particles were primarily composed of sea-salt, with majority of the sea-salt being sodium-chloride.  However, there was less chloride in these particles than sodium, which would indicate that chloride has escaped from the particles, probably end up as chlorine containing gas.  Since this experiment was focused on aerosols, we cannot say exactly how the blowing snow layer produces these aerosols, but this result has some important implications for the understanding of aerosol in Antarctica. 

Previously it had been thought that waves breaking in the open ocean was a major source of sea-salt aerosol in Antarctica.   Based on this idea, the amount of sea salt aerosol found in ice cores was thought to be an indicator of how far the site where the ice cores were extracted was from the open ocean, and therefore that sea-salt aerosol in ice cores could be used to determine how much of the ocean around Antarctica was covered by sea ice. The findings of this project suggest that this relationship is more complex - air that was moving quickly from the interior of the Antarctic continent often had a higher sea-salt aerosol content than air that had moved slowly from the open ocean.   The amount of sea-salt aerosol in the air, or in an ice core maybe a better indicator of the amount of snow-covered sea ice and wind speed than distance from the open ocean.    In contrast to this result, is the essentially omni-present small sulfate particles that do likely come from the open ocean, however these are separate from the larger sea-salt aerosol particles, contain much less overall mass and also don?t correlate with where the air came from or with wind speed. 

Last Modified: 11/07/2018
Modified by: Peter F Decarlo