Background on Ozone 
What is ozone?- Why is ozone higher on mountain tops?
- What are the impacts of ozone?
Why is ozone higher on mountain tops?
During an average summer day ozone levels do not change much throughout the day at elevations above about 3000 feet.
During a pollution event ozone concentrations can reach unhealthy levels at higher elevations but stay relatively lower in an adjacent valley. This mountain top ozone pollution is a result of higher background concentrations, less mixing of the air (that results in elimination of ozone through surface contacts and chemical reactions) and faster transport of pollution from a larger region.
 | The planetary boundary layer is an invisible zone above which air masses are more affected by regional weather and pollution than by localized mixed air.
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 The mixing layer is affected by local topography, winds and pollution emissions. Ozone gets eliminated when mixed with other chemicals and when making contact with any surface. |
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Watch the movie of ozone concentration changing by hour on an average summer day (no major pollution event) at a high elevation (Mt. Washington- 6,288 feet) and low elevation (Pinkham Notch- 1,500 feet) site. Low-elevation ozone concentrations usually rise at midday when temperatures and solar radiation are highest and ozone formation occurs faster than ozone elimination. At high elevation, ground-level ozone levels remains relatively constant throughout the day with little elimination since air is less mixed above the planetary boundary layer.
Go back to real-time ozone page to look at a number of paired high and low elevation sites to see if concentrations differ right now.
