[10] Norwegian scientists had observed the gradual acidification of the country's fresh waters through much of the 20th century, but it was only with the publication of pioneering work on acid rain by Svante Odén, in the late 1960s, that the causes became apparent.
[11] Ottar observed that thousands of lakes in Norway had become acidified and biologically impoverished due to industrial and power plant pollution from countries such as Britain, France, Germany, and Luxembourg.
[12] In 1970, he was appointed director of the OECD-sponsored Long-Range Transboundary Air Pollution Project[13] and championed cooperative international efforts to monitor the problem of acid rain, despite resistance from the countries concerned and the stark political divisions of the Cold War era.
As Dr Rachel Emma Rothschild notes, in a detailed account of his work: "Ottar was given the opportunity to organize a study of unprecedented scale on acid rain, but had little recourse to set the agenda, police the countries withholding financial contributions, or rectify their poor participation... As a result, knowledge about the transport of air pollution was substantially increased—though, as Ottar lamented, in the end the research was not enough to prompt international action on the environmental threat of acid rain.
"[18] In the early 1980s, Ottar became one of the first scientists to describe the mechanism by which harmful chemicals produced at mid-latitudes can be transported, via the atmosphere, to the Arctic – a phenomenon called global distillation.