Can air conditioners remove harmful PM2.5 particles?

According to the U.S. Environmental Protection Agency (EPA), conventional wall-mounted split air conditioners generally do not effectively remove fine particles from indoor air. Their filters primarily prevent larger particles from accumulating inside the equipment.

PM2.5 particles measure 2.5 micrometers or less in diameter, roughly 30 times smaller than the width of a human hair. They can penetrate deep into the lungs, and some can enter the bloodstream, increasing the risk of respiratory and cardiovascular diseases.

For more effective filtration, the EPA recommends checking whether an air conditioner's filter meets the Minimum Efficiency Reporting Value 13 standard or higher. Such filters must be compatible with the equipment and properly installed to work effectively.

A wall-mounted air conditioner. Photo from Pexels

In Singapore, where more than four in five households have air conditioners, according to the latest government survey, prolonged haze has raised questions about how effectively these appliances filter PM2.5 particles.

The city-state has experienced its longest stretch of unhealthy air quality since September, with its Pollutant Standards Index (PSI) exceeding 100 since Oct. 5. The PSI measures air quality based on six pollutants, including PM2.5, larger particles known as PM10, and gases such as sulfur dioxide and carbon monoxide. Readings above 100 indicate unhealthy air quality.

Liu Zheng, from Nanyang Technological University's School of Materials Science and Engineering, told The Straits Times that household air conditioners primarily recirculate and cool indoor air, while their filters are designed to capture larger dust particles.

Rajasekhar Balasubramanian, from the National University of Singapore's College of Design and Engineering, similarly said conventional air conditioner filters are generally ineffective at removing fine particulate matter.

Singapore's National Environment Agency (NEA) warns that PM2.5 can enter air-conditioned buildings through outdoor air intakes and gaps, potentially accumulating to unhealthy levels during haze episodes.

To reduce exposure, the EPA recommends using appropriately sized portable air purifiers or upgrading filters in compatible central air conditioning systems.

The NEA recommends high-efficiency particulate air filters for capturing fine particles. It also advises consumers to consider an air purifier's clean air delivery rate (CADR), which measures the volume of filtered air the device delivers.

A higher CADR generally allows an air purifier to clean an enclosed room faster, although the device must be appropriately sized for the space.