The reactions of sulfur oxides to form sulfuric acid are quite
slow. Sulfur dioxide may remain airborne for 3-4 days.As a consequence
acid rain derived from sulfur oxides may travel for hundreds
of miles or even a thousand miles.
Nitrogen oxides may persist for only about one half day and
therefore may travel only tens or hundreds of miles.
Once airborne, the sulfur and nitrogen oxides eventually come
down in one form or another. Where they come down depends on
the height of the smokestack and the prevailing weather conditions.
In general, prevailing winds in North America transport pollutants
from west to east or northeast.
The nine largest coal burning states are in the Midwest and
the Ohio River valley. It is estimated that two thirds of the
acid rain in the Northeast and Eastern Canada comes from these
Blue arrow shows the upper winds that travel from the west
to the east or northeast. Winds travel from the mid-west to the
In addition, a copper-nickel smelter in Sudbury, Ontario,
just north of Lake Huron is the most significant sulfur oxide
source in Canada. The winds may also carry the sulfur oxide clouds
to the Northeast in the U.S. where it may be converted to acid