酸雨
Sulfur dioxide is the principal contributor to acid rain, causing respiratory disorders, impairing visibility, harming the health of fish and wildlife, and degrading lakes and ponds. Research has shown lakes and streams in New England have been slow to recover from the effect of acid rain, compared to some in Wisconsin, New York and Pennsylvania. Acid rain brings with it mercury deposition, and together they cause tremendous damage to human health and the environment. Research by the Hubbard Brook Research Foundation recently identified nine suspected mercury hotspots in the northeastern U.S. and Canada. Harvard University economist Robert Stavins estimates about $1 billion per year has been saved in the United States by cleaning up since the Acid Rain Program went into effect.