SINGAPORE – Many who take up gardening love bringing the outdoors inside. It is a fantastic way to beautify our living spaces and lift our mood. These benefits of indoor greenery are especially appreciated when we are stuck at home during the haze.

But can our potted plants actually improve indoor air quality? I am asked this question all the time when the haze blankets Singapore.

The popular belief that plants double as natural air purifiers usually stems from the famous 1989 NASA Clean Air Study, which looked into ways to clean the air in sealed environments such as space stations.

Subsequent studies have also shown that plant leaves can trap fine particles from the air.

To understand what plants can actually do, it helps to look at the two main components of air pollution that threaten our health: toxic gaseous compounds called volatile organic compounds (VOCs) and fine particulate matter.

During the haze in Singapore, our primary health hazard is PM2.5 – microscopic particles of soot, ash and dust suspended in the air.

Leaves and soil play a big role

Plants absorb VOCs through their stomata – microscopic pores in leaves that open during photosynthesis for gas exchange.

But much of the heavy lifting is done below the surface, where the soil microbiome plays the dominant role.

Bacteria and fungi in the potting mix ingest gaseous toxins as air naturally diffuses through the substrate.

Once absorbed, the plant and these microbes metabolise the pollutants into harmless by-products.

Meanwhile, the waxy outer cuticle of leaves acts as a passive trap, physically trapping (adsorbing) specific chemical compounds.