A study of air trapped in Greenland\'s snowpack indicates atmospheric levels of carbon monoxide in the 1950s were higher than now, a U.S. researcher said. Researcher Vasilii Petrenko, an assistant professor of Earth and environmental sciences at the University of Rochester in New York, concluded CO levels rose slightly from 1950 until the 1970s, then dropped to present-day values. Petrenko\'s first-ever study and its finding contradicts computer models that had calculated a 40 percent overall increase in CO levels during the same period, the university said Wednesday in a release. \"The CO decline coincides with improvements in combustion technology, in particular the introduction of catalytic converters in automobiles,\" said Petrenko. \"CO emissions were declining even as fossil fuel use was increasing.\" Petrenko said he and his team began their research by extracting air from the Greenland snowpack at various depths. After analyzing the samples, they created a CO history for the arctic over the last 60 years, showing that levels have been in decline since the 1970s despite a global increase in the number of vehicles being driven. \"It seems that no one thought to study carbon monoxide in the Greenland snowpack before our work,\" said Petrenko. \"Also, the difficulty of taking the samples and making measurements may have discouraged some researchers.\"