Sources and Effects of Air Pollution

Cavity and Turtle Lake Fires - 2006Air pollutants affecting our National Forests can be divided into two groups: primary and secondary pollutants. Primary pollutants come directly from sources such as industrial facilities, automobiles and forest fires. These include sulfur and nitrogen compounds, particulate matter, and toxic metals such as mercury. Secondary pollutants, such as ozone, are formed when primary pollutants undergo chemical reactions in the atmosphere.

USS MinntacPollutant Deposition
Deposition occurs when compounds of various types of air pollution are deposited on the earth's surface through rain, clouds, snow, fog, or as dry particles. The amount of deposition received in a given area is affected both by the concentration of pollution in the atmosphere and the way in which it is deposited. This is because general factors such as climate, predominant meteorology and topography of a region can influence how much pollution reaches the area from both local and distant sources, as well as how much of that pollution actually impacts the earth's surface via the various wet and dry forms.

There are several types of ecosystem effects associated with deposition which tie to the form of pollutant being deposited. These include acidic deposition ("acid rain"), heavy metals (including mercury) and excess amounts of nitrogen.


Pollution Transport

Most air pollutants can be transported great distances from their source to impact lands far away.  The graphic at the left shows where (in orange) the air came from on the haziest days in the BWCAW. 

For their regional haze plan the State of Minnesota estimated the contribution of the neighboring states to visibility impairment in the BWCAW.  The analysis showed that while Minnesota is the largest, many other states contribute to the problem. In addition it was estimated that approximately half of Minnesota's impact was due to emissions from Northeastern Minnesota.








Learn more below on the major air pollution problems affecting the Forest.

Fine Particulates and Visibility

Mercury Deposition

Nitrogen and Sulfur Deposition

Ozone (smog)

Taconite Harbor Power PlantTwo excellent general reference documents describing air quality sources and effects in Minnesota and the Midwest are:

  • Minnesota Pollution Control Agency (MPCA) annual air quality report 
  • Lake Michigan Air Directors Consortium (LADCO) technical report