What is the problem with A?
It has the right idiom, and as far as I can tell it's just a little wordy.
Is that it?
Providing initial evidence that airports are a larger source of pollution than they were once believed to be,environmentalists in Chicago report that the total amount of pollutant emitted
annually by vehicles at O'hare International Airport is twice as that which is being emitted
annually by all motor vehicles in the Chicago metropolitan area.
A.as that which is being emitted annually by all
A is wrong because of parallelism issues. 'pollutant emitted' is not parallel to 'being emitted'. Secondly, usage of 'that which' is incorrect and awkward.
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