Particulates are usually washed from leaves by rain or irrigation, and are therefore more harmful during dry periods. Weather and pollutants Air currents carry all air pollutants. Air movements and geographic features influence pollutant concentration, chemical structure, and the duration of tree exposure to pollutants. Air temperature determines vertical movement of air pollutants. Under normal conditions, warm air near the soil surface causes pollutants to rise vertically.
Pollutants rapidly become diluted and blown away by upper level winds before contacting many trees.
These inversions usually occur in narrow valleys close to mountain ranges, and near large bodies of water. Temperature also influences a pollutant's chemical reaction rate. When the temperature is high, more photochemical oxidants are produced. These oxidants cause more severe damage during sunny hot weather and less damage during cool cloudy weather. Atmospheric moisture causes pollutants to become solutions, increasing their toxic potential.