Description: The lines show monthly average ozone for these regions:

• blue, northern midlatitudes (30°N to 50°N),
• green, northern semi-tropics (10°N to 30°N), and
• orange, equatorial (10°S to 10°N).

Comments: There is a trend for greater average amounts of ozone at greater distances from the equator. In all three zones ozone levels vary in a one-year cycle, with the amount of variation greater at greater distances from the equator. It appears that average ozone levels in the midlatitutes reached a minimum around 1994, but there is not an obvious long term trend closer to the equator.

Source: NASA TOMS, on line.

© 2001, 2002 by Wm. Robert Johnston.
Last modified 26 December 2002.
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