Jim Haywood, Michigan Department of Natural Resources & Environment
Stephanie Hengesbach, Michigan
Department of Natural Resources & Environment
The meteorologists generously contribute their time, energy, and know-how to the Ozone Action program. In addition to the Michigan Department of Environmental Quality 's meteorology staff, expertise is added from nearby areas including Indiana, Illinois, Wisconsin, and the Canadian Ministry of the Environment. They come together for a conference call to discuss the air quality forecast.
Ozone Action Day Forecasting
The following conditions are often conducive to high levels of ground-level ozone in the air we breathe:
- high temperatures, usually mid-80s or above,
- limited cloud cover, and
- low winds.
These conditions create the potential for excessive ozone levels.
For your reference, this brief description of the factors considered by the meteorology team will show the science involved in forecasting Southeast Michigan's Ozone Action days.
- Solar insolation/ultraviolet radiation
Ground-level ozone is produced photochemically and, thus, requires a significant amount of solar insolation to provide the energy required by the photochemical process.
Exposure of an object to the sun.
- Cloud cover
Cloudless skies create prime conditions for high amounts of solar insolation. Still, because the photochemical process can start at lesser amounts, a completely cloudless sky is not necessary.
The meteorologists must be attentive to a number of different degrees of cloud cover and even to the types of clouds present on days that might be forecast as Ozone Action days. They must also consider time of day for various types of cloud cover.
High temperatures increase ozone levels because they are favorable to the chemical reaction and also increase the amount of hydrocarbon emissions in the air. High temperatures also result in more evaporation of hydrocarbons, making a double contribution to the formation of ground-level ozone.
- Wind direction
Southwest winds are generally associated with high ozone days for three reasons:
- They push hot summertime temperatures into the area.
- They tend to transport ozone and ozone precursors from industrial areas upwind of Detroit to the area.
- They often act, during a lake breeze, to push ozone precursors into the stable layers of the nearby Great Lakes where the chemical reactions that form ozone are accelerated before the pollutant moves and is pushed on-shore.
- Wind speed
Low wind speeds (less than about 10 mph) enable the accumulation of precursors and subsequent formation of high concentrations of ozone. At speeds above about 10 mph, emissions are diluted too rapidly for ozone to accumulate significantly.
- Ozone precursors
An in-depth study of weather conditions and expected emissions gives the best possible estimate of when ozone-conducive conditions likely will be problematic for the quality of the air we breathe.
- Hydrocarbon Emissions
Emissions come from human activities include driving, industrial manufacturing, fueling, lawn mowing, and painting. It is necessary to consider how time of day, day of week, and various activities might affect these emission-generating activities.
- Oxides of nitrogen (NOx)
Oxides of nitrogen both produce and deplete ground-level ozone. Which effect NOx has on air quality is determined by the amount of it in the air, relative to the amount of hydrocarbons present. Ultraviolet radiation, time of day, temperature, wind direction, and wind speed are also important in determining whether NOx produces or destroys ozone.