Air pollute stats for Middlesex Co in 1998
| County | Middlesex Co |
| State | Massachusetts |
| Data from year | 1998 |
| Total number of days monitored | 365 |
| Good air | 321 (87.95%) |
| Moderate air | 37 (10.14%) |
| Unhealthy for sensitive groups | 5 (1.37%) |
| Unhealthy for all | 2 (0.55%) |
|
| Worst pollutants |
|
| Carbon monoxide | 56 (15.34%) |
| Nitrogen dioxide | 0 (0.00%) |
| Ozone | 73 (20.00%) |