Wildfires are a source of air pollution, which impacts air quality in proximity to and at great distances from fires. Wildfire smoke exposure is seasonal and episodic, with exposure levels and durations that can vary considerably. Exposure to wildfire smoke is associated with numerous health effects, including an increased risk of mortality and exacerbation of respiratory diseases. In Canada, the health risks of wildfire smoke are communicated to the public via air quality (AQ) alerts, when levels of wildfire smoke are currently or are forecasted to be relatively high, posing a risk to the general population. To better understand the population at risk due to wildfire smoke, a population-based exposure metric was developed based on geolocated AQ alerts and population data. This metric, measured in person-days, quantifies the number of people at risk of experiencing adverse health effects of wildfire smoke during a given time period. Data from the 2023 wildfire season were used to evaluate the metric. The greatest numbers of person-days were associated with population centres and regions that experienced periods of prolonged, intense smoke exposure. For example, Toronto, a large population centre, had 12 days with AQ alerts issued, corresponding to 33.5 M person-days. This approach could be expanded to other environmental or extreme weather conditions.