Atmospheric ethene (C2H4; ethylene) amounts have been retrievedfrom high-resolution solar absorption spectra measured by the Jet PropulsionLaboratory (JPL) MkIV interferometer. Data recorded from 1985 to 2016 from adozen ground-based sites have been analyzed, mostly between 30 and67° N. At clean-air sites such as Alaska, Sweden, New Mexico, or themountains of California, the ethene columns were always less than1 × 1015 molec cm−2 and therefore undetectable. In urbansites such as JPL, California, ethene was measurable with column amounts of20 × 1015 molec cm−2 observed in the 1990s. Despite theincreasing population and traffic in southern California, a factor 3 decreasein ethene column density is observed over JPL over the past 25 years,accompanied by a decrease in CO. This is likely due to southern California'sincreasingly stringent vehicle exhaust regulations and tighter enforcementover this period.
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