Year	SOx	NOx	CO
1940	17.6	6.8	81.5
1950	19.8	9.3	86.1
1960	19.7	12.8	88.1
1970	28.3	18.3	100.2
1980	23.4	20.4	77.0

Source: US Department of Commerce, Bureau of the Census, Statistical Abstract of the United States 1990.

The above table shows the total air pollution over the years 1940-1980.  Each year is shown as representative of that decade.

The figures in the table are in millions of metric tons.  SOx refers to any type of sulfur dioxide, NOx refers to any nitrogen oxide, and CO is carbon monoxide.

It is quite clear from the table that the levels of SOx and NOx have been increasing rapidly over the years.  These are both potentially dangerous greenhouse gases, which can also have negative health effects.

Overall changes in the level of any chemical in the environment will have many impacts, both foreseeable and unforeseeable.  As rates continue to rise and fall, the environment will change with them.