Monitoring Methods

In Alberta, outdoor air quality is monitored using continuous, intermittent and passive methods. Precipitation is also monitored.

Continuous monitoring provides nearly instantaneous measurements of pollutant concentrations and data are stored in one-hour average time blocks. Continuous sampling involves drawing air through a commercial analyzer calibrated to produce an output that is proportional to the ambient pollutant concentration. This gives the greatest resolution but is costly, due largely to the capital and operating costs involved.

Intermittent monitoring includes collecting a 24-hour average pollutant concentration, once every sixth day, in accordance with the National Air Pollution Surveillance (NAPS) monitoring schedule. This usually involves collecting pollutants using reactive tubes, absorbents or filters. Intermittent samples need to be analyzed at a laboratory to determine air pollutant levels. Because of the time and effort needed to analyze samples, data may not be available for several months after the sample is collected.

Passive monitoring provides a cost-effective solution for monitoring air quality at locations where continuous monitoring is not practical. Passive samplers collect air pollutants without the need for electricity, data loggers or pumps. Pollutants are transferred from the air to a reactive surface and laboratory analysis is required to determine the pollutant concentration. Passive sampling is useful for studying long-term trends, and a network of samplers can be used over a large area to determine the spatial variation of pollutant levels. Samples are collected over a one-month period, providing monthly average concentrations.

Precipitation samples are collected weekly using automated precipitation sampling equipment, and analyzed by a laboratory for pH, sulphate, nitrate, ammonia, chloride, phosphate, sodium, potassium, calcium and magnesium. The resulting data is used to determine acid deposition.