At last, some good news about the environment.

A recent analysis of core samples taken from Greenland’s ice sheet shows that levels of a common form of air pollution have dropped almost to preindustrial levels. Just take a look at the graph below:

Helle Astrid Kjr NBI This graph of acid content in Greenland ice cores shows how the acidity of the atmosphere rose from the 1950s through the 1970s before declining sharply.

“We can see that the acid pollution in the atmosphere from industry has fallen dramatically since manmade acid pollution took off in the 1930s and peaked in the 1960s and 70s,” Dr. Helle Astrid Kjaer, a postdoctoral researcher at the Center for Ice and Climate at the University of Copenhagen’s Niels Bohr Institute, said in a written statement.

But some say it’s a bit early to break out the champagne.

“The conclusion that acid deposition to the Greenland ice sheet has returned to preindustrial levels is surprising,” Dr. William R. Stockwell, a professor of chemistry at Howard University in Washington, D.C., told The Huffington Post in an email. “However, I would not conclude that atmospheric acid production has returned to preindustrial levels everywhere.”

Stockwell said it would be “a stretch” to conclude that acid deposition over the United Staes has returned to preindustrial levels.

Paul Vallelonga NBI The ice was drilled in Greenland before being transported back to the lab for analysis.

Of course, a decline in any form of air pollution is good news. As Kjaer told The Huffington Post in an email, “It is great to see that international agreements actually do work in limiting harmful substances in the environment.”

Kjaer attributed the welcome decline in atmospheric acid to the pollution-control measures mandated in the U.S. by the 1970 Clean Air Act and by similar legislation enacted in Europe.

The measures limited emissions of sulfur dioxide and nitrogen oxides from power plants, automobile tailpipes and other industrial sources. These pollutants are known to combine with water and other substances in the atmosphere to form sulfuric and nitric acids, which can fall to Earth as acid rain.

Acid rain causes a range of environmental ills, including soil depletion, lower crop yields and fish kills. It can also make trees more vulnerable to disease and hasten the deterioration of buildings and vehicles.

The finding reveals little about other air pollutants, such as the greenhouse gas carbon dioxide, a byproduct of the burning of fossil fuels. Atmospheric levels of CO2 have risen relentlessly in recent years (see graph below).

NASA Scripps National Oceanic and Atmospheric Administration Levels of carbon dioxide in the atmosphere have risen sharply in recent years.

Given the carbon dioxide problem, Kjaer said it was “even more important to start limiting the CO2 in the atmosphere if we want to limit global climate change.”

For the new research, published Sept. 1 in the journal Environmental Science and Technology, Kjaer and her collaborators at the institute and the Alfred Wegener Institute in Bremerhaven, Germany, used a new technique to measure the pH (level of acidity) of melted ice from core samples drilled in 2012 in the upper layers of the ice sheet.

The samples, which contained ice that was laid down in the form of snow from the years 1900 to 2004, showed the acid levels rising at first and then falling sharply.

“We can directly see the fluctuations from year to year,” Kjaer said in the release.

How about a toast to no more fluctuations?