Technical Information Bulletin - Thermal Inversions
MAY 2003 Version
The application of agricultural fumigants during or prior to or during a thermal inversion can cause airborne levels of pesticides to be trapped and concentrate in the vicinity of the application. This can be problematic, particularly in areas where residential properties are in close proximity to the treated area. Applicators should not apply agricultural fumigants during conditions that favor thermal inversions or when weather indications suggest a thermal inversion is eminent. The following information has been compiled to help applicators recognize weather factors that favor the formation of a thermal inversion.
DEFINITION - A thermal inversion is where cool air is trapped by warm, resulting an extremely stagnant pocket of air at the earth's surface. Thermal inversions are usually most pronounced in valleys and low-lying areas. Thermal inversions occur when there is 1) a large temperature variation (25F and 30F degrees) between daytime high and nighttime low temperatures; 2) clear skies and calm winds at night. This allows the surface air to cool more rapidly than the surrounding air which traps or caps the surface air.
RECOGNITION - The National Weather Service states that thermal inversions can occur during the entire Massachusetts growing season. They are most likely to occur in Spring and fall when large temperature shifts are most common, but inversions are not uncommon in summer and winter months..
If your local weather forecast calls for the following conditions at night (especially in the spring and fall months), you should reschedule the application for a day when the conditions are not favorable for a thermal inversion would be the best option.
- clear skies,
- calm winds
- and a temperature variation of 25 degrees F or more between daytime and nighttime lows temperatures.
HAZARDS - Under a typical use situation small amounts of pesticides that escape a treated area are dispersed into the atmosphere without ever reaching an appreciable concentration. During a thermal inversion escaping pesticides that become trapped at the surface may concentrate in a limited geographical area. This could lead to an exposure incident affecting humans, animals and residential or commercial properties.
PRECAUTIONS - Avoid making pesticide applications prior to or during a thermal inversion, or prior to or during conditions that favor inversions. Strict adherence to all label requirements, careful weather monitoring and common sense are the first line of defense against drift and exposure. The responsibility of making a proper pesticide application is yours. The Massachusetts Pesticide Bureau (617) 626-1781, is available to assist you in making the best choices in the planning and execution of your pesticide applications.
REFERENCE INFORMATION - Below you'll find some useful links for additional information on thermal inversions as a link to the National Weather Service.
Thermal Inversion Links
|
