Those April showers bring more than May flowers these days. Much of the rain that falls on the United States, and elsewhere on Earth, carries a hidden, and harmful, ingredient: acid.
Human-caused "acid rain" has fallen regularly since the Industrial Revolution Began 200 years ago. But only since the 1950s -- with the proliferation of automobiles, coalfired boilers, and smelters accelerated by postwar industrial expansion -- has acid rain become an acute environmental problem.
The severity of the problem is expected to increase, especially in light of economic forecasts that point to greater dependence on coal in the future.
Social and political consequences are following the acid rain. One sign of the depth of concern was the large attendance this week at a special meeting in Springfield, Va. of officials of 32 Eastern states and Canada to discuss the problem.
US Environmental Protection Agency (EPA) chief Douglas M. Costle called the conference "one of EPA's most important ever." He says acid rain represents "one of our most genuine and serious environmental problems."
According to environmental scientists, the most severe effects of acid rain at present are being felt in northern Europe, Japan, Canada, and the Eastern US.But countries of the Southern Hemisphere soon will have to cope with the problem also.
Nitric and sulfuric oxides from auto exhausts and factory smokestacks are converted, in the atmosphere, into dioxide acids. Eventually, they fall to earth with rain or snow -- often hundreds of miles from the point of origin.
This precipitation increase the acidity of bodies of water, causes buildings and stone monuments to deteriorate, kills or injures aquatic life, and burns holes in leafy vegetables.
Scientists say it is only a matter of time before drinking water in certain areas approaches unacceptable levels of acidity.
Because acid rain has "snuck up on us" over a period of years, Mr. Costle says, there are few historic measurements of the acidity of soil and water with which to compare current figures. A federally sponsored assessment program has begun, but it may be several years before a reading of trends is available.
Mr . Costle says he supports President Carter's goal of energy independence through the conversion of utilities from gas and oil to coal. But he says this must be accompanied by coal washing, flue-gas scrubbing, nitrogen oxide controls , and other clean-air measures.
Second only to the environmental dimension of acid rain is its political dimension. The US is a "net exporter" of acid rain into the Canadian atmosphere. And many "have" states in the industrial Midwest are the source of acid rain that falls on agriculturally intensive "have-not" states in the South and West.
"Concerns on the part of the public have made controls a political issue," says Raymond Robinson, director of Canadian Environmental Research. "And we are committed to them."
Mr. Robinson says there is an "inescapable relationship" between industrial pollution on either side of the border and acidity in Canadian and American lakes.
The EPA is beginning to negotiate a clean-air pact with Canada.
And Mr. Costle says the agency soon will begin using provisions within the Clean Air Act that allow a regional rather than state-by-state approach to air-pollution problems. "We will use our authority in favor of states with stringent controls" on pollutant emissions, he says.
Among the near-term hopes in the fight against acid rain, scientists say, are special coal-cleansing techniques that might remove 10 percent of the potential sulfur released into the atmosphere, a new burner for pulverized coal that is capable of reducing nitrogen oxide emissions by two-thirds, and industrial incentives to encourage the early retirement of older, highly polluting generating stations.