In practice, it's usually fairly evident, and usually defined by provinces. It's part of operating permits or particular regulations where there's a definition of upstream, downstream, and sampling points. Most of the impingement and ambient monitoring is defined in the operating permit, and there's usually an agreement where you're going to do it and sign off on the sampling point.
So there are processes already; that has never been an issue. It's the gaps in-between that aren't there, particularly on diffuse sources. If you look at the national pollutant release inventory, it only has information on releases from point source facilities, or from defined operations. It doesn't have information on, for example, roads, road dust, or any of those kinds of sources, or car or vehicle emissions, because those are not the sorts of things that an individual consumer is going to go out and measure—for example, their tailpipe—and report.
Those sorts of estimates have to be done by government, and the monitoring of air quality in the city has to be done by government.