Ambient NO₂ levels in Canada currently vary between 1.16 and 14.96 ppb, with the national average being 8.43 ppb.

Mann-Kendall long-term trend analysis indicates that NO₂ levels have significantly decreased at 87% of sites.

Declining transportation emissions have had the largest influence on decreasing NO₂ levels.

Changepoint detection shows that legislated transportation emissions reductions lead to subsequent decreases in NO₂ levels.

There is ∼2 years of lag between emissions reductions and the reporting of reductions.