Air and soil
In most cases, aspergillosis is caused by a type of mold called Aspergillus fumigatus. Aspergillus mold can often be found on dead leaves, compost piles and other decaying vegetable matter, stored grain, and even foods and spices. The mold spores may be carried indoors on shoes and clothing and can grow on carpeting.  Aspergillus mold is unavoidable. Outdoors, it's found in decaying leaves and compost and on plants, trees and grain crops. Inside, the spores — the reproductive parts of mold — thrive in air conditioning and heating ducts, insulation, and some food and spices.  Aspergillus is widely distributed from the arctic region to the tropics. Aspergillus species are frequently found in air and soil.As concerns indoor air quality the most important species are Aspergillus fumigatus, Aspergillus flavus, Aspergillus clavatus, Aspergillus niger, Aspergillus versicolor. 1 Medical Effects. 2  As concerns health, the most important species of Aspergillus are Aspergillus clavatus, A. flavus, A. fumigatus, and species from the group of A. niger, and A. Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli. Viewing the fungi under a microscope, Micheli was reminded of the shape of an aspergillum (holy water sprinkler), from Latin spargere (to sprinkle), and named the genus accordingly. Aspergillus species are highly aerobic and are found in almost all oxygen-rich environments, where they commonly grow as molds on the surface of a substrate, as a result of the high oxygen tension. Its natural habitat is in hay and compost. some species withstand heat eg; Aspergillus fumigatus (pathogenic type) these are commonly found in compost. This type of mold can be found everywhere indoors (prefers damp materials) and outdoors. Aspergillus can produce mycotoxins – these are often found in contaminated foodstuff and are hazardous to the consumer. Many toxins of this type of mold have been identified and depend greatly on genus and species. Aspergillus (/ˌaespərˈdʒɪləs/) ˌæspərˈdʒɪləs is a genus consisting of a few hundred mold species found in various climates. worldwide Aspergillus species are highly aerobic and are found in almost all oxygen-rich environments, where they commonly grow as molds on the surface of a substrate, as a result of the high oxygen tension. Aspergillus lives in the environment. Aspergillus, the mold (a type of fungus) that causes aspergillosis, is very common both indoors and outdoors, so most people breathe in fungal spores every day. It’s probably impossible to completely avoid breathing in some Aspergillus spores Back to Top Causes. Aspergillosis is caused by a fungus (Aspergillus). The fungus is commonly found growing on dead leaves, stored grain, compost piles, or in other decaying vegetation. It can also be found on marijuana leav Aspergillosis. Aspergillosis is an infection caused by Aspergillus, a common mold (a type of fungus) that lives indoors and outdoors. Most people breathe in Aspergillus spores every day without getting sick. 
http://my.clevelandclinic.org/health/diseases_conditions/hic-aspergillosis http://www.mayoclinic.org/diseases-conditions/aspergillosis/basics/causes/CON-20030330 http://www.moldbacteria.com/mold/aspergillus.html https://en.wikipedia.org/wiki/Aspergillus http://caltexmoldservices.com/section/mold_library/aspergillus/ https://en.wikipedia.org/wiki/Aspergillus http://www.cdc.gov/fungal/diseases/aspergillosis/causes.html http://www.nytimes.com/health/guides/disease/aspergillosis/overview.html http://www.cdc.gov/fungal/diseases/aspergillosis/index.html
where is aspergillus found