Ro Acosta takes an air quality reading on the outskirts of Mexico City. He began measuring ultraviolet radiation in 1993 to complete master's-level research as a Trent student. His work inspired the city to begin broadcasting hourly air quality readings on local television. Acosta continues to monitor UV and ozone levels for a doctoral project.

By Martha Tancock
Trent Communications

When there's not enough ozone in the stratosphere to block harmful ultraviolet (UV) rays, air pollution can do the trick. The thicker the better.

        That's why Mexico City is an ideal lab for Trent grad student Ro Acosta. With 20 million dwellers driving four million vehicles in a tropical valley, Acosta's home town is one of the most polluted cities in the world. To complete his master's thesis, Acosta needed a thick blanket of daily smog. He was measuring how UV rays are attenuated -- thinned out, reduced -- by the urban atmosphere. Because the city sprawled across a valley, Acosta could also collect comparative readings in the suburbs and on the higher outskirts, where the air is cleaner. He couldn't have done that in Canada. The air's too clean, the geography too flat.

        The Earth's ozone layer, hovering in the stratosphere 25,000 metres above sea level, filters dangerous UV rays before they reach ground level. This is where it belongs. But where there is automobile pollution, there is ozone at ground level. It is a powerful oxidant and major component of smog (a chemical stew created by a reaction of sunlight, ozone and nitrogen oxide). It can be highly corrosive, especially in heavily populated cities like Mexico City, Los Angeles and Tokyo where it is trapped by surrounding hills. It not only burns your lungs (respiratory problems are endemic), it deteriorates metals, plastics and vegetation.

        Until 1993, Mexico City inhabitants didn't know just how lethal their air was. That changed when Acosta began doing his master's- level thesis under the direction of environmental studies professor and ozone expert Wayne Evans.

        Mexico City's environmental ministry got wind of his air quality, ozone and UV radiation monitoring stations, endorsed Acosta's work and invested in more equipment. Using information he supplied, the ministry began broadcasting hourly air pollution conditions on local television. Now, four years later, it also posts updates on the Internet (www.calivad-del-aire.gob.mx) using data from an expanded network of 13 air quality stations around the city.

        After Canada, Mexico City was the first in the world to set up a UV radiation monitoring system and to publicly broadcast UV index levels. "People know how to deal with temperature, but they don't know how to behave with the burning potential of the sun," says Acosta.

        As in all equatorial cultures, Mexicans have always worn big hats and taken siestas during mid-day to escape the sun at its most intense. But in cosmopolitan centres like Mexico City, "people have forgotten all about it." And because UV-B rays (the fast-acting kind that cause sunburn and skin cancer) are invisible -- they are not hot and you can't see them -- "we must remind them" to take precautions, says Acosta. Stand in the shade, wear hats, cover up.

        Canada is the world leader in establishing a UV radiation index and ozone safety standards, now endorsed by the World Health Organization. Canada has set a safe ground-level ozone standard at 82 parts per billion, the U.S., at 110 parts per billion. In Mexico City, ozone levels exceed 110 parts per billion more than half the days of the year, says Acosta. "It's considered normal here."

        When the ground-level ozone reaches 270 parts per billion, as it did Sept. 27 -- a Saturday! -- Mexico City bans the use of private automobiles, stops running government vehicles, orders industry to reduce emissions by 50 per cent and closes gas stations. It's a short- term contingency plan that reduces the ozone level to safe levels within a day. It came into being since Acosta began supplying the city's environment ministry with hourly readings.

        Using instruments modelled after Trent's, he was recording levels every minute for one and a half years at three stations -- downtown, in the suburbs and at a high altitude site outside the city. He discovered that in the densely populated downtown, pollution creates a shield against UV-B rays. You are safer from UV-B rays there than in the suburbs or outskirts where the air is cleaner. In fact, people in downtown Mexico City are exposed to UV-B rays to the same extent as people in Toronto, even though they are closer to the sun and under a particularly thin layer of stratospheric ozone. The smog provides a shield to UV-B rays on polluted days.

        Acosta came to Trent in 1985 on a Canadian International Development Agency scholarship. He completed his M.Sc. in 1995 under Evans. He continues to gather data for a doctoral research project he expects to pursue under the Trent professor. In the meantime, he also continues to collaborate with the local environment ministry, television station and other institutions to improve the air quality monitoring in and around Mexico City.

        Acosta's research has also helped promote Trent as a leader in UV radiation monitoring in Spanish-speaking countries, says Acosta. They know the equipment has been modelled after Trent's and supported by Evans. Acosta's work attracted interest from UV index experts around the globe at the World Meteorlogical Organization conference this summer in Switzerland. Trent International Program director David Morrison joined Canada's Ambassador to Mexico Marc Perron as honorary signatories to an agreement between the City of Mexico and the Instituto Technológico de Estudios Superiores de Monterrey, which has set up an air quality monitoring station on its campus as a result of Acosta's work.

         His pioneering research will take him well into the future and will no doubt influence environmental policy in his country, says Evans.