an atmospheric zone about 19 to 80 km (11.8 to 49.7 mi) above the earth's surface, in which photochemical reactions take place
See chemosphere in American Heritage Dictionary 4
(kēˈmə-sfîrˌ, kĕmˈə-)
noun
The region of the atmosphere from 30 to 190 kilometers (20 to 120 miles) above the earth's surface, in which photochemical reactions initiated by solar radiation occur.