Assessing acid deposition: Advances in the state of science

NAPAP has a long history of conducting research related to acid deposition. Throughout the 1980s NAPAP supported a large number of research projects that confirmed the link between SO₂ and NO_x emissions and acidic lakes and streams hundreds of miles away. Recent research is confirming the tight link between emissions of SO₂ and the amount of several different forms of sulfur in the atmosphere and in precipitation, and improving our ability to measure acid deposition. Research has continued since 1990, albeit on a smaller scale, to increase our understanding of how acid deposition affects trees, soils, lakes, streams, coastal waters, and building materials such as stone and copper. Some of the areas where the most research has been done include: the importance of calcium in mediating soil and forest response to acidification; the role of nitrogen in acidification and recovery from acidification; and the role of nitrogen deposition in coastal ecosystems. In addition, substantial advances have been made in understanding the human health impacts of fine particles, including sulfates and nitrates, which are briefly mentioned here.