Particulate matter (PM) describes airborne solid particles and liquid droplets. It is generated from a variety of sources such as car exhaust, other combustion sources, smoking, aerosols, cooking, wind-blown soil, road dust, and mould growth. Particles with a diameter of 10 micrometers or less, denoted as PM10, can lodge in the trachea or in the bronchi of the respiratory system. The biggest impact of PM on human health, however, is associated with long-term exposure to fine particles of 2.5 micrometer diameter and smaller (PM2.5). Particles of these sizes can reach the alveoli in the lungs and long-term exposure to PM2.5 has been associated with increased mortality risk.
Exposure to particulate matter, especially for sensitive populations such as children and individuals with pre-existing health conditions, can lead to short-term and long-term adverse health effects. In children, for example, exposure to particulate matter can lead to a chronic reduction in lung growth rate and a deficit in long-term lung function. It has been estimated that 3% of cardiopulmonary and 5% of lung cancer deaths globally are attributable to particulate matter.
Guidelines for particulate matter are usually expressed in terms of the concentration of PM2.5 or PM10. The World Health Organization (WHO) air quality guideline values for PM2.5is 10 µg/m3 for the annual average and 25 µg/m3 for the 24-hour mean. The WHO air quality guideline value for PM10 is 20 µg/m3 for the annual average and 50 µg/m3 for the 24-hour mean. In Canada, the Canadian Ambient Air Quality Standard (CAAQS) agreed upon by the Canadian Council of Minister of the Environment (CCME) sets a target for PM2.5 of 30 µg/m3 averaged over a 24-hour period.
With respect to indoor PM, Health Canada recommends that, at a minimum, the concentration of PM2.5 indoors be lower than the concentration of PM2.5 outdoors. An indoor PM concentration that is higher than outdoors indicates a strong indoor source of PM that needs to be addressed. Based on our experience, one of the most common reasons for high PM concentrations in the indoors is the obstruction of supply and return vents (see Figure 1 courtesy of AirVironment Canada). Smoking, the use of incense sticks, and a poor quality vacuum system can also contribute to high PM concentrations in the indoor environment.
The following steps can be taken to reduce the concentration of particulate matter in the indoor environment: