Arenas with a concentration of CO above 25 ppm37
| Year | Province or state | Total arenas tested (n) | Arenas with air contamination (n) |
|---|---|---|---|
| 1971 | Minnesota | 18 | 13 |
| 1976 | Quebec | 16 | 13 |
| 1978 | Massachusetts | 8 | 6 |
| 1980 | Ontario | 4 | 1 |
| 1984 | British Columbia | 64 | 32 |
| 1989 | Quebec | 10 | 3 |
| 1989 | Quebec | 45 | 23 |