Air Quality trends

• Air Quality Trends HomeOzone Hourly Trend
• Ozone Seasonal Trend
• Ozone Annual Trend
• Ozone Regional Trend
• Ozone Historical Trend
• Particle Pollution Hourly Trend
• Particle Pollution Annual Trend
• Particle Pollution Historical Trend

Ozone Hourly Trend

Looking at ozone data in different ways is a good approach to learn more about how ozone behaves over time and space. So we have presented the data in different ways to help you learn more about ozone in Maine. On this page we'll start with the most basic information about ozone.

First, let's review basic information about Ozone:

1. Ozone is very unstable, which means it breaks down readily.
2. Ozone production is photochemically driven. This means that sunlight is needed to enable the chemical reactions which produce ozone and reform ozone after it breaks down.

   • Therefore, it becomes obvious that ozone levels will most often be lower at night; and
   • Ozone levels will be reduced when the sun is lower in the sky during October through March.

The graph below illustrates the daily ozone trend in various regions around the state. At most sites, the afternoon values tend to be the highest of the day. This is important information if you are sensitive to ozone and want to know when you need to take precautions.

This graph also illustrates the difference that elevation has on daily ozone values. Ozone values at higher elevations show less diurnal variation, i.e. they don't drop as low overnight or rise as high during the day. One reason ozone levels are higher at elevated sites is because there are fewer ozone sinks aloft. An ozone sink is something that reduces the ozone concentration. One example of an ozone sink is vegetation - ozone is deposited on the leaves of trees so it is removed from the air.

The ozone hourly trends were calculated by taking the average for each hour of the day across the entire ozone season for a representative monitoring site in each region and plotting the resulting values as continuous lines.