TABLE 2.

PM2.5 measures of air pollution in the causal pathway as a worked example of this approach

Hazard surveillance	Exposure surveillance	Health effect surveillance	Intervention options
Ambient levels of PM2.5 ↑ Routinely and continuously monitored in real time in many locations ↓ Needs geographically denser monitoring sites or GIS modelling ↑ The quality of the data is excellent and assured, and the data source is valid, reliable and sensitive Air Quality Health Indicator (AQHI) ↑ Health risk based ↑ A single indicator synthesizing many air pollutants and health effects	Ambient levels shown to be good surrogate for personal exposure ↓ Many micro-environments and complex PM chemistry complicate picture	Hospitalization – Respiratory and Cardiac Mortality – Respiratory and Cardiac ER visits – Respiratory ↑ Data routinely collected by CIHI; can be analyzed ↓ Needs complex time series methods ↓ Lacks specificity; effects related to co-morbidity/age ↓ “Harvesting” (displacement) effect on mortality* ↓ Health outcomes are the tip of the pyramid, so the full extent of health effects is not demonstrated	↑ Can be promptly acted upon, with public health benefit (e.g., air quality advisories to reduce exposure, and industrial shutdowns to reduce emissions) ↑ Useful to promote long-term policy re: power generation, transportation, etc. ↑ Can be used to assess interventions ↓ Complex health messaging with advisories

Note: Critical commentary is that of the authors, with ↑ indicating a positive attribute, and ↓ indicating a negative attribute.

^*“Harvesting” refers to deaths precipitated by a pollution incident that would have occurred within a short period of time in the absence of the high-pollution event. (Smith 2003).

^*Smith 2003