Methane and carbon monoxide in OH chemistry: The effects of feedbacks and reservoirs generated by the reactive products

Abstract Carbon monoxide and methane are the two largest direct sinks of atmospheric OH. Globally the reaction between OH and CO provides the largest direct sink of OH, which is about twice as large as the reaction between OH and CH 4 . However, neither CO nor CH 4 affects OH only by direct reactions. In fact, the direct reaction of OH with either CO or CH 4 initiates a series of reactions and products, which also affect the atmospheric OH and can thus be considered as feedbacks. We developed a method to calculate the total contribution of either CO or CH 4 to OH by tracing a series of reactions and products, which are initiated by the direct reaction of OH with either CO or CH 4 . With this tracing technique, we show that atmospheric methane, along with its feedbacks, may remove as much as more atmospheric OH than carbon monoxide, although CO is widely accepted as the largest sink of the atmospheric OH.

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