Global Aerosol Research is Heating Up
David R. Brooks, PI, GLOBE Aerosol Monitoring Project
Global aerosol research is becoming a hot topic for atmospheric scientists. A two-part feature article in Science News (vol. 160, Nos. 13 and 14, September 29, October 6, 2001) is the latest high-visibility report on aerosols. After being virtually ignored for decades, research suggesting that dust is transported from arid regions in Africa, Asia, and elsewhere across both the Atlantic and Pacific oceans has been confirmed by satellite and ground-based measurements.
This isn't just a little bit of dust, either. Scientists estimate that 700 million metric tons of dust per year is picked up by the wind over North Africa alone. Of this, about 2 million metric tons is lifted high in the troposphere where it can travel thousands of miles. In April 2001, dust from China crossed the Pacific Ocean to North America. It reduced sunlight in Boulder, Colorado, USA, by an estimated 25 percent. Joseph M. Prospero, an atmospheric scientist at the University of Miami in Florida, USA, has found that African dust crossing the Atlantic Ocean constitutes as much as half the breathable particulates in Miami's summer air.
Some scientists believe that the mineral content of dust helps to fertilize soil far from the source of that dust. (Dust from The Sahara is rich in iron, for example.) When it is deposited over the ocean, it is thought to be a cause of algae blooms.
Recently, scientists have found spores and fungi attached to dust. Previously, it had been assumed that ultraviolet (UV) radiation would sterilize dust particles during their high-altitude journeys in the atmosphere. However, it is now clear that some spores and fungi survive - perhaps by "hiding" in small irregularities in the surface of dust particles - and can reproduce in places thousands of kilometers from their origins.
Aerosols interact with other atmospheric components, too. For example, surface ozone levels are affected by the amount of sunlight reaching the earth's surface. Aerosols reduce the amount of sunlight, and recent research has shown that ozone prediction models can be significantly in error when assumed values of aerosol optical thickness are used in place of actual measured values. You should not be surprised to hear that, especially in urban areas where high ozone levels are a persistent problem, AOT measurements are rarely available.
The global consequences of natural and manmade activities that produce aerosols continue to surprise scientists. Despite the renewed interest in aerosols, the global ground-based monitoring network is still very sparse, and will remain so for the foreseeable future. This is especially true in urban areas and in regions of the world such as Africa and Asia where deserts are major dust sources. So, it's especially important for students around the world to monitor aerosols near their source and as they travel around the globe.