NASA's AERONET (AErosol RObotic NETwork) program consists of a group of ground-based remote sensing instruments in the U.S. that can determine the amount of aerosols, or tiny particles of pollutants, that are in the air over a given location. The goal of this ground network is to assess the optical properties of aerosols, specifically how much sunlight they scatter and absorb, and to provide a double-check of aerosol data as gathered by satellites.
The Canadian subnetwork, called "AEROCAN," which stands for Aerosols in Canada, is particularly important because of Canada's large forested area and corresponding number of the number of forest fires.
Brent Holben, an atmospheric scientist at NASA's Goddard Space Flight Center, Greenbelt, Md., leads the AERONET program in the U.S. that the Canadian program mirrors. "AERONET consists of a series of ground-based remote sensing sun photometers that measure aerosols globally," Holben said. NASA and various federal agencies, universities and institutes around the world have established these ground-stations, and it has been expanding at a rate of greater than 10 percent per year.
Holben said, "The AERONET ground network continually verify the accuracy of data NASA collects from instruments aboard NASA's Terra satellite." Terra looks at aerosols from space down to Earth, while this project looks at them from the Earth up toward space. When AERONET or AEROCAN data are combined with satellite data in atmospheric computer models, they can provide a complete, continuous and time dependent picture of pollution over a region which environmental managers can use to create health forecasts. NASA and Natural Resources Canada's Canada Centre for Remote Sensing and the Environment Canada helped Canadian scientists set up and maintain the pan-Canadian "AEROCAN" subnetwork as part of the AERONET program's world-wide expansion.
One particular area of interest for the AEROCAN network is western Canada. Forest fires in western Canada have an important affect on sun photometer measurements. According to Norm O'Neill, an AEROCAN scientist from the CARTEL (remote sensing) Centre at the Université de Sherbrooke in Sherbrooke, Québec, Canada, 80 percent of the summertime optical effects (such as haze) seen at sites such as Thompson, Manitoba and Waskesiu, Saskatchewan can typically be traced to smoky pollutant particles from Western Canadian fires. These smoky conditions often create visibility problems for motorists and pilots.
Such was the case during the first week in July, when forest fires flared up north of Québec City in eastern Canada and AERONET was in full operation. Those fires generated a mass of aerosols that was swept as far south as Washington, D.C. A brownish haze resulting from the smoke covered major cities such as Toronto, New York, Philadephia and Baltimore during the weekend of July 6th and 7th.
The sun photometer located at NASA's Goddard Space Flight Center measured the highest aerosol loading ever recorded in the eastern U.S., approaching values of 1.5 to 2. An aerosol optical depth of 1 means that only 37 percent of the direct sunlight is getting through the aerosols in the atmosphere. "On Sunday July 7th, the aerosol optical depth values, indicative of the concentration of pollutants in the air approached a value of 6, which was never recorded before in this area," Holben said. An aerosol optical depth of 6 means only 0.25 percent of the direct sunlight is getting through the aerosols to the ground, making for diffused light and hazy conditions.
"We even have some optical evidence that forest fires from as far away as Siberia can have a significant effect on the amount of particles over North America, but clearly nowhere near the influence of Canadian sources," said O'Neill, who is currently stationed at Goddard where he is collaborating with the AERONET group on aerosol optical research projects.
The expansion of the AERONET network in Canada and ongoing collaborative research projects are funded by NASA, Natural Resources Canada's Canada Centre for Remote Sensing, the National Research Council of Canada, Environment Canada, and the National Science and Engineering Research Council of Canada.
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For images of aerosols from Canadian fires, see:
For more information on the AERONET and AEROCAN programs, go to: