The United States and Canada have launched a project to determine whether the methods they use to measure acid rain produce compatible results. Apparently, the U.S. and Canadian findings may not be comparable because of differences in the way they collect and analyze data.
The U.S. separately collects precipitation from snow and rain as well as dry, windblown material. The samples are gathered and analyzed weekly. The Canadians use instruments that collect only water. They gather and test their samples monthly.