Research began as project in freshman science class

By William J. Cromie

Gazette Staff

Smog levels have decreased in the nation's three largest metropolitan areas, according to a research study that began as a student project by Harvard freshmen.

The study also revealed that levels of ozone, smog's main ingredient, have not gone up in the past 15 years despite a 60 percent increase in vehicle traffic. These findings were reported on Tuesday in the Journal of Geophysical Research.

There's bad news mixed with the good, however. "Despite two decades of air-pollution control efforts, ozone concentrations have not decreased as expected," notes Daniel Jacob, Gordon McKay Professor of Atmospheric Chemistry and Environmental Engineering. He is the teacher who encouraged his students to study ozone, which remains the number-one hazardous air pollutant in the United States.

Ozone concentrations located miles above the surface clean pollutants from the air, contribute to global warming, and protect us from dangerous ultraviolet radiation. Near the surface, it kills farm crops and endangers the health of children, the elderly, asthmatics, and those with respiratory diseases like bronchitis and emphysema.

Three years ago, Jacob and research associate Jennifer Logan assigned freshmen the task of determining how air pollution changed in the students' hometowns from 1980 to 1995. The Environmental Protection Agency (EPA) had reported a decrease during this period, so Jacob and Logan expected to find a drop in ozone. But none of the students could find a trend up or down.

"They were bored with those results, so we decided to look at other parts of the country," recalls Jacob. The students checked the Los Angeles area and found a surprising drop in ozone, especially during summer afternoons. Later, reductions were also found for the New York and Chicago metropolitan areas.

One of the main reasons, strangely enough, is a lack of trees rather than a lack of cars and trucks, minivans, and sports utility vehicles.

Tree Pollution

Ozone comes from two sources: nitrogen oxides and hydrocarbons. The oxides result from burning gasoline, natural gas, coal, diesel fuel, and other so-called fossil fuels. Hydrocarbons are easily vaporized compounds containing hydrogen and carbon. The two interact with each other as well as with sunlight, and, in the course of a complex series of these interactions, form ozone.

Small dust and soot particles added to the mix give it the foggy, sometimes brownish look, which people call smog. These small particles, known as aerosols, can penetrate deep into human lungs, and the EPA considers them a major health threat.

Trees and other vegetation are a major source of hydrocarbons, a fact that underlies the infamous half-truth from former President Ronald Reagan: "Air pollution comes from trees."

Hydrocarbons also come from the tailpipes of vehicles and from gasoline pumps, which has led to laws requiring catalytic converters and seals on gas-pump nozzles. Such regulations have reduced hydrocarbons produced by human activities but not from nature.

In Los Angeles, New York, and Chicago, human-generated hydrocarbons are high, but emissions from trees are low. Therefore, controlling the high anthropogenic hydrocarbons reduces total ozone levels.

This has not been the case in the rest of the country. Take Boston, for example. It's a small city surrounded by green suburbs that provide lots of natural hydrocarbons for making ozone.

Looking in the Wrong Place

Ozone levels also have not decreased because the EPA and state agencies put the emphasis on the wrong ingredient until recently. Their pollution-control efforts focused on hydrocarbon emissions. It was believed that controlling such emissions would whittle ozone down to healthy levels.

That didn't happen. In 1990, about one-third of the U.S. population still breathed air with unhealthy levels of ozone. To determine why, a National Academy of Sciences panel did a study called "Rethinking the Ozone Problem."

"This report made a clear statement that controlling hydrocarbons alone was not going to solve the problem," says Jennifer Logan, who was a member of the panel. "It recommended that pollution control concentrate on nitrogen oxides."

Catalytic converters, which cut both nitrogen oxides and hydrocarbons, are one way to do this. "They reduce nitrogen oxides from each car," Logan points out. "But because the number of cars has increased, emission levels have been flat in most areas." Nitrogen from the air burns at high temperatures in vehicle combustion chambers. It combines with oxygen, gets blown out of the exhaust, and becomes available for sunlight to turn into ozone.

"You need these high temperatures to get full benefit from the fuel burned," Jacob points out. "That's one reason why pollution-control agencies have been hampered in their efforts to reduce ozone concentrations."

Toughening Standards

Despite the difficulties, the EPA intends to toughen the air quality standard for ozone. "That means many areas now in compliance with the standard will come out of compliance," Jacob says. "Boston is one of those areas."

Jacob and Logan are also researching the possibility that emissions from Asia, blowing across the Pacific on westerly winds, will smother efforts to control air pollution in this country. The situation is similar to pollutants from coal-burning plants in the Midwest being carried by winds to New England.

"As emissions from China rise rapidly, we'll face a tougher and tougher time meeting our air-pollution standards, particularly for ozone," Jacob predicts.

Each state measures its ozone levels and reports them to the EPA, which compiles a database for the whole country. Harvard students used that database to find places where concentrations decreased or remained the same. Much of the research for the report published this week was done by students Arlene Fiore and Jeffrey Yin, who followed up on the classroom exercise.

Fiore, who graduated last year, spent two summers working on the data and wrote her senior thesis on the results. As a reward, her name appears as the first author of the Journal of Geophysical Research paper. The co-authors are Jacob, Logan, and Yin.