Simply put, this is when temperatures in the troposphere (lowest layer of the atmosphere) are colder at lower altitudes than at higher altitudes, which is just the opposite of what normally occurs. Inversions can occur as the result of weather fronts moving through an area, or because of winds blowing over ground that is frozen over with ice or snow, or because of frigid lake or ocean conditions. When an inversion occurs it prevents air from circulating vertically, which can result in pollutants being trapped at low altitudes. Inversions also disrupt radio and radar transmissions.