Measurements of the preceding sort are of ambient air – that is, air where people might breathe it and not in workplaces. These measurements are usually reliable and available. A possibly trickier measurement is of where the pollution comes from, often a question addressed by emissions inventories. In BC and other Canadian jurisdictions facilities are required to report to Environment Canada on an annual basis their releases of toxic substances to the air. There is a natural tendency in self reporting to under-report, notwithstanding which the inventory resulting tracks releases in an interesting way. At the NPRI we can see a complex example in the historical report summary of Canfor's NPRI reporting in recent years. Criticisms of such reporting has been done by Scott Vaughan, Commissioner for Sustainable Development and the Environment in his Fall 2009 report.