New research shows that human pollution of the atmosphere with acid is now almost back to the level that it was before the pollution started with industrialisation in the 1930s. The results come from studies of the Greenland ice sheet and are published in the scientific journal, Environmental Science and Technology. By drilling ice cores down through the kilometre-thick ice sheet, the researchers can analyse every single annual layer, which can tell us about ... pollutants in the atmosphere. Acid in the atmosphere can come from large volcanic eruptions and human-made emissions from industry. For many years, there has been a quest to solve the problem of measuring acidity in the porous annual layers of the ice and now scientists from the Niels Bohr Institute have succeeded [by employing] a Continuous Flow Analyses or CFA method. The CFA system can ... distinguish whether the emissions come from volcanic eruptions, large forest fires or industry. The researchers can therefore filter out both volcanic eruptions and forest fires in the assessment of industrial pollution and the new results are revolutionary. "We can see that the acid pollution in the atmosphere from industry has fallen dramatically since humanmade acid pollution took off in the 1930s and peaked in the 1960s and 70s. In the 1970s, both Europe and the United States adopted the 'The clean air act amendments', which required filters in factories, thus reducing acid emissions," explains [researcher] Helle Astrid Kjr.