Particulate matter in the air is a “mixture of microscopic solid particles and liquid droplets suspended in air”.1 It may contain a variety of substances, including harmful aerosols, dust, smoke, and fumes. Particles of this nature that are smaller than 2.5 µg in diameter are classified as fine particulate matter (PM2.5) and are a concern for human health because they can penetrate deep into the respiratory system and damage lung tissue.
1. Ontario Ministry of the Environment, Conservation and Parks. Air quality in Ontario 2017 report [Internet]. Toronto (ON): Queen’s Printer for Ontario; 2017. Fine particulate matter; [updated 2019 Jun 19; cited 2019 Oct 29]; [about 4 screens]. Available from: https://www.ontario.ca/document/air-quality-ontario-2017-report/fine-particulate-matter