PM2.5 refers to fine particulate matter 2.5 micrometers or smaller in diameter, tiny enough to penetrate deep into lungs and even enter the bloodstream. PM2.5 is the most health-concerning air pollutant, contributing to respiratory disease, cardiovascular problems, and premature death. Sources include vehicle emissions, industrial processes, residential burning, and wildfire smoke. Air quality monitoring emphasizes PM2.5 due to its health impacts. The Air Quality Health Index (AQHI) incorporates PM2.5 levels in health risk assessments. Wildfire smoke has become a major PM2.5 source, with Canadian communities increasingly experiencing hazardous air quality days requiring public health responses and activity restrictions.