My response would be that the appropriate way to measure emissions and the adequacy or lack thereof of emissions has to vary on a substance-by-substance basis. If we're talking about a chemical substance that is a carcinogen, for example, you have to ask the question: Where does it have an impact? If it has a strictly local impact, then you need to measure the emissions of the substance within that local airshed. If the substance has some transboundary impacts, then we need to look at those impacts as well, because we're putting it up in the atmosphere and we're causing cancer in other countries.
The third example, of course, is greenhouse gas emissions. This is strictly a personal answer, but I think it's completely inappropriate to measure those based on our land mass. Just because we happen to have inherited the largest and least-inhabited land mass in the world doesn't give us the right to emit more than another country when the problem is a global problem.
So if the problem is a local problem, measure it on a local level. If it's a global problem--