smell of soil after rain is due to
Petrichor The term was coined in 1964 by two Australian CSIRO researchers, Isabel Joy Bear and Richard G. Thomas, for an article in the journal Nature.[1][2] In the article, the authors describe how the smell derives from an oil exuded by certain plants during dry periods, whereupon it is absorbed by clay-based soils and rocks. During rain, the oil is released into the air along with another compound, geosmin, a metabolic by-product of certain actinobacteria, which is emitted by wet soil, producing the distinctive scent; ozone may also be present if there is lightning.[3] In a follow-up paper, Bear and Thomas (1965) showed that the oil retards seed germination and early plant growth.[4]
Acid rain The corrosive effect of polluted, acidic city air on limestone and marble was noted in the 17th century by John Evelyn, who remarked upon the poor condition of the Arundel marbles.[2] Since the Industrial Revolution, emissions of sulfur dioxide and nitrogen oxides into the atmosphere have increased.[3][4] In 1852, Robert Angus Smith was the first to show the relationship between acid rain and atmospheric pollution in Manchester, England.[5]