Air Quality by City

Pick a city and see how its air pollutants have changed since the 1970s: annual trends and the month-by-month detail from the NAPS monitoring network

Pick a city and see how the air its residents breathe has changed since the 1970s. These are the actual measurements from Environment and Climate Change Canada’s National Air Pollution Surveillance (NAPS) network — the monitoring stations behind the national indicators on the Air Quality page — averaged across each city’s stations. The broad pattern is steep improvement. Sulphur dioxide — the acid-rain pollutant — has fallen most. Carbon monoxide and nitrogen dioxide trace vehicle exhaust, so their high readings in the 1970s reflect the era before catalytic converters and unleaded fuel — carbon monoxide has since dropped by roughly 90%. The exception is fine particulate matter (PM2.5), which has been pushed up in recent years by wildfire smoke — most visibly in the western cities in 2023.

Month-by-month detail

Monthly resolution reveals the seasonal rhythm: summer ozone, winter particulates, and the sharp spikes when wildfire smoke arrives. Pick a city and a pollutant to see one series at full size, and drag the slider beneath the chart to zoom into a period. Try Edmonton or Calgary with PM2.5 around 2023 to see the impact of a record smoke season.

Download data

Source & method. Values are 1-hour-basis concentrations from the NAPS network (per-station). For each city we average all of its stations, so a city with several monitors is smoothed across them. Units are µg/m³ for PM2.5 and ppb for the gases (ppm for CO).

Coverage & how far back. Fifteen cities are shown: the major metros plus a national spread, including Yellowknife for recent wildfire smoke and the long industrial records of Windsor and Sudbury (the full network is larger; the list is trimmed here to keep the menu manageable). The gases (NO₂/SO₂/O₃/CO) reach back to 1974 and PM2.5 to the late 1990s. From 2005 on the values are NAPS’s pre-computed Annual Summaries (validated per-station means); the earlier years are aggregated here from NAPS’s raw hourly files on the same 1-hour basis (a monthly mean needs ≥50% of the month’s hours; an annual mean needs ≥6 months spanning all four quarters). The two eras join smoothly — Toronto SO₂, for instance, reads ~2.5 ppb in both 2004 and 2005. Smaller communities are omitted to keep the selector manageable; recent validated data lags the calendar year by ~12–18 months.

Cities vs. the national picture. These city averages complement the population-weighted national indicator on the Air Quality page (which is the standard reference but only national and from 2009). Here the trade-off is reversed: city-level and back to the 1970s, but a simple station average rather than a population-weighted exposure estimate. All data are published under the Open Government Licence – Canada.