This article is from the Ozone Depletion: Stratospheric Chlorine and Bromine FAQ, by Robert Parson firstname.lastname@example.org with numerous contributions by others.
The total amount of chlorine in the stratosphere has increased by
a factor of 2.5 since 1975 [Solomon] During this time period the
known natural sources have shown no major increases. On the other
hand, emissions of CFC's and related manmade compounds have
increased dramatically, reaching a peak in 1987. Extrapolating
back, one infers that total stratospheric chlorine has increased
by a factor of 4 since 1950.