Factors that Contribute to the Formation of Ozone

In addition to the presence of VOCs and NOx, there are other factors which contribute to the formation of ground level ozone. These are the types of factors that MDEQ meteorologists take into consideration when forecasting Ozone Action days for our area.

Solar insulation, or high levels ultraviolet radiation (sunlight) is required to initiate the ozone-forming photochemical reactions. Sunlight stimulates the VOCs and NOx chemicals to recombine to create ground level ozone.

In addition, the amount of cloud cover contributes to ozone formation. When there are few or no clouds, or only high transparent clouds, solar insulation is more able to penetrate to ground level, enabling the photochemistry that generates ground-level ozone to occur. When cloud cover increases, the likelihood of elevated ozone levels decreases.

Temperatures over 80° also influence the formation of ozone. Higher temperatures enhance the ozone formation chemistry and increase the evaporative emissions of volatile organic compounds. The higher the temperature, the more likely elevated levels of ozone will occur.

Wind direction, especially winds out of the south-southwest can contribute to ground level ozone. South or southwesterly winds typically bring warmer weather to West Michigan, or transport existing ozone from upwind locales, such as Chicago.

Low wind speeds (less than 10 MPH) are necessary for the accumulation of precursors of ozone formation (VOCs and NOx) and the subsequent formation of ozone. Higher wind speeds tend to dilute or disperse emissions, however they can still transport ozone from other locations.

Dry weather allows ozone to remain in the air; therefore low levels of precipitation can contribute to ozone formation. Scattered showers do not produce enough precipitation to completely eliminate ozone, but widespread rain will cleanse the atmosphere of ozone.

The positions of fronts are also considered in ozone formation because of their potential to affect cloud cover, precipitation, and changes in the air mass.

The West Michigan Clean Air Coalition is a partnership of businesses, academic institutions, government agencies, industry, and non-profit organizations in Kent, Ottawa, Muskegon, and Kalamazoo counties working together to achieve cleaner air in the region through the education and promotion of voluntary emission reduction activities.