Transfer of organic Br and Cl from the Biosphere to the Atmosphere during the Cretaceous/Tertiary Impact: Implications for the stratospheric Ozone Layer

[摘要] Following the Cretaceous/Tertiary (K/T) meteoriticimpact some 65Myr ago, large portions of aboveground terrestrial biomasswere burned. As a result, large amounts of various trace gases were injectedto the atmosphere, inducing a wide range of effects on climate andecosystems. Here, it is commented on the previously unaccounted for emission tothe atmosphere of methyl bromide (CH₃Br) and methyl chloride(CH₃Cl) from extensive biomass burning that followed the impact. Basedon reported biomass burning emission rates of the above organohalogensrelative to CO₂, it is estimated that their emissions from global firesresulted in tropospheric mixing ratios of around 20-65.8ppbv organic Cl and110-390pptv organic Br. The above calculated mixing ratios of organicchlorine and bromine are more than an order of magnitude greater than their present,anthropogenically perturbed level and, although the ocean ultimately mightabsorb them, we argue here that they could still remain in the atmospherefor many years, and a substantial fraction could be transported to the stratosphere, thussubstantially affecting the ozone layer. This would haveled to very serious increases in short wavelength UV radiation reaching thelowermost atmosphere.

[学科分类] 大气科学