Alternaria alternata

Alternaria is a ubiquitous mold found almost everywhere in the country and is a normal agent of decay and decomposition as well as plant associated disease.  Alternaria pores are usually present in outdoor air throughout the year, frequently exceeding the number of pollen by 100- to 1000-fold or more, depending on environmental factors, such as water, nutrients, temperature, and wind.  In Arizona, Alternaria spore levels increase during the summer monsoon season and peak during the fall.  Airborne levels are affected by fall harvesting of crops and temperature inversion, trapping particulates including mold and pollen close to the ground.