Canada's ''minister of acid rain'' appears to have done his job. When Prime Minister Pierre Trudeau shuffled his Cabinet earlier this month, the minister of the environment, John Roberts, was promoted to the more important portfolio of manpower and immigration.
Mr. Roberts had been given his nickname by Canadian columnist Allan Fotheringham because Mr. Roberts had spent much of the time in his job complaining about acid rain, making frequent trips to Washington to drive home his complaints, and using diplomats and lobbyists to follow through.
The major point was to convince the Reagan administration that acid rain - airborne pollution - existed and was killing lakes, rivers, and fish in Canada and the northeastern United States.
Washington now appears to be taking the problem seriously.
Last week in Ottawa the new minister of the environment, Charles Caccia, signed an agreement on acid rain with Paul Robinson, the American ambassador to Canada. After years of disagreement the two countries are going to try to find out more about long-term pollution from cars, factories, and electric generating plants. The agreement aims to remove the guesswork about how airborne pollution travels.
The pact will fund the Cross-Appalachian Tracer Experiment (CAPTEX), which will follow the trail of air pollution in parts of North America. During September and October scientists will release three 500-pound batches of a rare inert gas into the air over Dayton, Ohio, and Sudbury, Ontario, two industrial areas that are major producers of acid rain.
A network of 85 ground testing stations in Canada and the US will sample the air for traces of the gas. Seven chase planes with testing equipment will follow the gas as it crosses state, provincial, and international boundaries, trying to pick up hints of the substance in the atmosphere.
The gas, perfluoro-monomethyl-cyclohexane, is not found naturally in the atmosphere and is used in few industries, so it will be easy to follow.
Scientists from Environment Canada say the gas is harmless and eventually will disappear into the atmosphere. But before it does, Canadian and US scientists hope to nail down the causes of acid rain with some certainty.
Scientists have long claimed that acid rain is pollution traveling long distances via the atmosphere and falling to the ground as rain, snow, or dry deposition. But they have not been able to pinpoint where it comes from. The Ohio Valley is suspect, as is the Sudbury basin with its huge smokestack at the International Nickel smelter in northern Ontario.
When CAPTEX has finished its work, it will leave an atlas of acid rain showing the path pollution travels in North America. The maps could take up to a year to draw, but once they are ready scientists should be able to show how cutting pollution in one area would reduce acid rain downwind.
The project will cost more than $2 million, and the US will pick up 90 percent of the cost.