Research has increasingly suggested that much of the Bay's pollution problems begin at smokestacks and tailpipes, some of which may be hundreds of miles outside the watershed.

Computer models indicate that about 27 percent of the nitrogen deposited in the Bay originates from air pollution, raising the question of whether that source of pollution could be economically controlled to help the Bay.

A new report hints that the answer may be "yes."

That opens the door for additional work to determine the economic and technical feasibility of controlling air pollution in places like Ohio, New York, West Virginia and Tennessee.

"We felt we had to start getting a handle on it now," said Rich Batiuk, associate director for science with the EPA's Bay Program Office. "We had to figure out if controlling air sources of nitrogen was even on the economic dart board, or if we were completely missing it."

Using computer models, the study determined that if the 1990 Clean Air Act amendments are fully implemented within the Bay watershed, they would reduce the amount of nitrogen entering the Chesapeake by about 5.3 million pounds - more than what enters the Bay from the entire Patuxent watershed.

The study by the Virginia-based consulting firm, E.H. Pechan and Associates Inc., then asked the question: If the smokestack and tailpipe controls in the Clean Air Act only benefited the Bay, how much would those nutrient reductions cost?

The answer was about $75 for each pound of nitrogen kept out of the Bay. The figure was reached by dividing the total cost of new emission controls by the amount of nitrogen kept out of the Bay.

By that measure, traditional means of nitrogen control, such as reducing runoff from agricultural land and upgrades of wastewater treatment plants, are far cheaper than additional air pollution controls.

Still, $75 is only about half the cost per pound of controlling nitrogen by other, more expensive techniques being used to meet Bay cleanup objectives, such as controlling runoff from existing urban areas.

Taking the analysis a step further, the study found that implementing Clean Air Act controls throughout the vast "airshed" that impacts the Chesapeake would reduce the amount of nitrogen reaching the Bay by about 11.5 million pounds - about as much as what washes out of the Patuxent and Rappahannock watersheds combined. But the per-pound cost would double as well.

Bay Program officials were encouraged by the study because they said it showed costs were "in the ballpark" of economic feasibility when examined strictly for a Chesapeake Bay benefit. Realistically, they noted, controlling nitrogen oxide emissions would also reduce urban smog, acid rain and pollution problems for other estuaries.

"It sure looks expensive at the outset," said Bill Matuszeski, director of the EPA's Bay Program Office, "but by the time you think about who all benefits from these reductions, it's a hell of a lot more people than live in the Bay watershed, and it's a hell of a lot more water than just the Chesapeake Bay."

The report comes at a time of growing interest in helping the Bay by controlling air pollution.

The Bay Program has a goal of reducing the amount of nitrogen and phosphorus entering the Chesapeake 40 percent by the turn of the century. While progress has been made with phosphorus, nitrogen has proven more difficult to control, in part because so much of it comes from the air.

Excessive amounts of those nutrients spur algae blooms which block sunlight to Bay grasses that provide habitat for fish and shellfish and food for waterfowl. When the algae die, they sink to the bottom and decompose in a process that depletes the water of oxygen needed by other organisms.

As the nitrogen reduction goal has proven difficult to reach, the role of air pollution has been getting a closer look.

Computer modeling at the EPA's Atmospheric Research and Exposure Assessment Laboratory the last two years has calculated that huge amounts of nitrates - a form of nitrogen - reach the Bay watershed as the result of nitrogen oxide (NOx) emissions from fossil fuel combustion in vehicles, power plants and industries.

The airshed that generates that pollution covers about 350,000 square miles, an area 5.5 times larger than the Bay watershed. In fact, the models estimate that about 60 percent of the nitrate deposition on the watershed originates from sources outside the three Bay states.

Some of that material, acting as a fertilizer, is absorbed by trees and plants, but much of it is washed into streams, rivers and, ultimately, the Bay. The Bay Program's Watershed Model, which calculates the transport of nutrients through the 64,000-square-mile Chesapeake drainage, estimates that 27 percent of all the nitrogen entering the Bay results from air pollution.

The new report offers the first look at not only the relative cost of air pollution versus other control measures to benefit the Bay, but also the costs of various options. Although large amounts of nitrogen deposition in the watershed come from outside the Bay states, it is less cost effective - strictly from a Bay perspective - to control those emissions, the report said.

The reason is that pollution from distant sources disperses before reaching the watershed. As a result, emissions from an individual source have less of an impact than a similar source close to the watershed. But, there are so many sources outside the watershed, their cumulative effect is large. That means controls are less effective and therefore more costly.

"You could look at an area like West Virginia, and it's probably the next most cost-effective place to obtain controls," said Jim Wilson, one of the authors of the Pechan study. "But once you get past West Virginia, the geographic distance tends to make the cost effectiveness a lot worse."

At the same time, the study indicates that some kinds of controls are more cost effective than others. For example, additional pollution controls on fossil fuel-burning power plants both inside and outside the Bay states are most cost effective, followed by additional controls on cars and trucks. Further controls on large industrial boilers, generally, are the least cost-effective option.

In a control scenario in which NOx emissions at utility smokestacks were limited to 0.15 pounds per million British thermal units produced throughout the Bay states, emissions were reduced 5.3 million pounds at a cost of $54 per pound. Expanding that stringent control throughout the airshed would reduce an additional 9.3 million pounds of nitrogen to the Bay, but at a cost of $119 per pound delivered to the Bay. Such a reduction is under consideration in states from Northern Virginia to Maine as part of an effort to control chronic summertime ozone problems.

Despite the costs, Bay Program officials say they may need to look beyond the Bay states in some instances.

The study shows, for example, that nitrogen deposition is not evenly distributed over the Bay watershed. Some of the highest nitrate deposition rates in the nation are in the Susquehanna River drainage. And air pollution accounts for more nitrogen flowing out of the Susquehanna - 43 percent - than any other river in the watershed.

In such places, Matuszeski said, the 40 percent reduction may not be met unless pollution from upwind areas, such as the Ohio Valley, are addressed.

"Pennsylvania has tried to make the 40 percent reduction, and they're going to fall short," Matuszeski said of nutrient plans for the Susquehanna watershed. "While there can't be a uniform solution throughout the Bay, there are some parts of the watershed, like the Susquehanna, where looking at this issue makes sense."

Air pollution controls may be even more important in the future. Once the 40 percent reduction goal is reached, the Bay states have committed to maintaining loads entering the Bay at those reduced levels despite anticipated growth in the watershed.

As other nutrient control efforts reach their maximum level of effectiveness, interest will likely turn to air pollution. An expanding population will mean more pressure on sewage treatment plants, more development, more driving and more demand for electricity, all of which could increase nitrogen loads to the Bay.

"It's something that we've got to have in our arsenal once we hit the 40 percent," Batiuk said. "Air has got to be an active part of our maintaining the nutrient loading cap."

More immediately, the report comes at a time when the Bay Program, along with environmental officials from other East Coast states, have suggested that the impacts of air pollution on water quality should be taken into account when setting regional policies.

Officials from the 37 states east of the Rocky Mountains and the EPA are participating in the Ozone Transport Assessment Group, which is trying to find a regional strategy to control the ozone pollution - or smog - which plagues many Midwestern cities and much of the Northeast.

Because the pollution that contributes to high ozone levels, particularly nitrogen oxides, can drift for hundreds of miles after being emitted, states often cannot meet federal ozone standards solely through actions within their own borders, leading to a regional approach.

Representatives from the Bay Program and northeastern states have tried to raise that issue with OTAG to urge that ozone reduction decisions also consider benefits to the Chesapeake and other coastal waters.

For example, reducing NOx emissions only in the summertime would help reduce ground-level ozone - which forms when NOx and other hydrocarbons mix in the sunlight on hot, summer days. But limiting those reductions to summer months would minimize benefits to waterways, where year round NOx deposition contributes to increased nitrogen loads.

"We've got to try to make a case for the Chesapeake on behalf of a number of other East Coast and Gulf Coast estuaries," Batiuk said. "We would prefer the OTAG states not lock into technologies and approaches like strictly seasonal or event-based controls for NOx emissions that would benefit the ozone attainment issue, but not recognize that loadings from atmospheric deposition impact the Bay system year round."

A follow-up study will try to identify all the beneficiaries of additional NOx controls - instead of just looking at benefits to the Bay - and allocate the costs of those emission reductions among the different beneficiaries to better determine the cost effectiveness of different strategies.

"It's immediately obvious to anybody who works in this area that if you're trying to reduce nitrate loadings, in the process you're also going to reduce particulate matter concentrations, because the NOx converts into nitrates, and you'll also reduce ozone concentrations," said Alan Krupnick of Resources for the Future, an environmental research organization working on the follow-up report.

In other words, reductions from a smokestack in Toledo not only reduces nutrient loadings to the Bay and other coastal waters, it will also help reduce pollution levels - and human health impacts of pollution - in Toledo and at points in between, such as Cleveland and Pittsburgh.

"It's a much more full picture of the role that improving the Bay could play on air quality generally," Krupnick said.

In addition, the study will examine various emission-trading scenarios within the airshed that contribute pollution to the Bay. "We would like to see what that looks like, and how the costs would be different," Krupnick said, "because it would be a lot less."

For a copy of the report, "Atmospheric Nitrogen Deposition Loadings to the Chesapeake Bay: An Initial Analysis of the Cost Effectiveness of Control Options," contact the Chesapeake Bay Program Office, 1-800-968-7229.