A few years ago, scientists searching for the causes of pollution in Tampa Bay began looking in a new direction: up. What they found has led to a major revision in Tampa Bay's pollution portrait. Like toxic contamination, air pollution has proven to be a far greater player than originally thought, contributing more than one-quarter of the bay's total nitrogen burden.

The pollution, also known as atmospheric deposition, comes from power plant emissions, industrial smokestacks and vehicle exhaust. All of these sources carry nitrogen oxides, or NOx, which can fall on the bay surface with rainfall, or as dust particles.

The emissions also contain significant quantities of potentially toxic contaminants such as mercury, lead and cadmium. In fact, experts estimate that 44 percent of the 7,000 pounds of cadmium annually deposited in the bay is carried by the atmosphere. Cadmium is found in paints, plastics and batteries, and emissions are linked to garbage-burning facilities.

The nitrogen contained in air pollution is of particular concern, because too much nitrogen can upset the delicate nutrient balance in the bay, sparking algae blooms. Research financed by the TBEP has shown that about 1,180 tons of airborne nitrogen fall directly on the bay each year. Another 7,000 tons settle on land in the bay's watershed, a portion of which eventually seeps into the bay through stormwater.

"It's hard for people to understand that what comes out of a smokestack or out of their car can potentially harm the bay,'' said TBEP senior scientist Holly Greening.

But while Tampa Bay managers now know how serious the problem is, they still have little direct evidence to tie the nitrogen fallout to specific polluters. They do know that stationary sources such as coal-fired power plants or garbage incinerators contribute about 66 percent of the nitrogen oxides released to the air in the Tampa Bay watershed, while vehicles and boats account for about 34 percent. But they can't say how much of those emissions generated locally actually wind up in Tampa Bay, since airborne contaminants may travel hundreds of miles before falling to earth.

Uncertainty also surrounds a proposal by Florida Power & Light Co. to burn a new, less expensive fuel, called Orimulsion, at its Manatee County plant. Emissions associated with this fuel could substantially increase annual nitrogen loadings to the bay, unless efforts to compensate for impacts are required.

However, these NOx emissions would represent only a fraction of the NOx currently emitted from coal-fired power plants in the region, such as those operated by Tampa Electric Company.

One thing seems definite: Air pollution will increase as more people, industries and automobiles descend on the bay region. The initial plan of attack for dealing with air pollution relies heavily on research.

This effort recently received a boost when Tampa Bay was selected to participate in the U.S. Environmental Protection Agency's Great Waters program, which focuses on atmospheric deposition and its effect on water quality. In cooperation with local communities, this program will sponsor a 3-year study to investigate where the atmospheric deposition is coming from and how large a role it plays in stormwater pollution.

Energy conservation also is a key component of the TBEP's strategy to reduce air pollution. One recommendation calls for the TBEP and local communities to identify the 100 most light- and energy-intensive businesses in the area and encourage their participation in existing programs that assist them in reducing energy use and, consequently, in saving money.