Changes in CH₄ and CO growth rates after the eruption of Mt. Pinatubo and their link with changes in tropical tropospheric UV flux

Abstract

Trace gas measurements from air samples collected weekly at a globally distributed network of sampling sites revealed sharp increases in the growth rates of CH 4 and CO in the tropics and high southern latitudes immediately following the eruption of Mt. Pinatubo on June 15, 1991. The eruption emitted ∼20 Mt SO 2 into the lower stratosphere. Calculations made with a radiative transfer model show that UV actinic flux in the wavelength region 290–330 nm was attenuated by ∼12% immediately after the eruption due to direct absorption by SO 2 , and that it was perturbed for up to 1 year after the eruption due to scattering by sulfate aerosols. We suggest that the decreased UV flux decreased the steady‐state [OH] and led to the observed anomalously large growth rates for CH 4 and CO during late‐1991 and early‐1992.