By James Hoorman, Hoorman Soil Health Services
After a dry summer, the smell of rain is often refreshing but maybe a little less so to farmers at harvest time! People can often sense it is going to rain. This “pre-rain” smell comes from ozone formed when oxygen (O2) in the atmosphere is spilt through electrical charges in the clouds to form ozone (O3). Ozone is blown down from the upper atmosphere and has a sharp odor, somewhat like chlorine or burnt wires. This pre-rain smell is a good indication a storm is brewing before the pleasant smell of rain occurs.
Recent research shows that the smell of rain is caused by soil actinomycetes or actinbacteria. Scientist have a name for it called petrichlor (pronounced pet-try-cure). As rain infiltrates the soil, it causes the actinomycetes to form spores which are released along with geosmin, a chemical that creates that earthy soil smell when soil is tilled.