A recent study from the University of Birmingham suggests that indoor air pollution can reach unhealthy levels, even when outdoor air quality is good.

Over two weeks, researchers used low-cost sensors and advanced techniques to monitor particulate matter (PM) in three homes. Their findings revealed that indoor pollution levels were higher and more variable than those outside.

One home even exceeded the World Health Organisation`s (WHO) 24-hour PM2.5 limit on nine separate days, emphasizing the need for household-specific air quality monitoring.

The study, published in Scientific Reports, is the second paper from the McCall MacBain Clean Air Fellows, who are part of the philanthropically funded Master`s program in Air Pollution Management and Control at the University of Birmingham.

Catrin Rathbone, co-author and Clean Air Fellow stated: "Our research highlights the importance of monitoring indoor air pollution, as homes can have unhealthy air even when outdoor conditions are good. PM levels varied significantly between households, demonstrating that a single monitoring location is insufficient."

The study found that factors like household location, ventilation, and occupancy patterns influenced pollution levels, revealing the complexity of indoor air quality.

Owain Rose, another co-author and Clean Air Fellow added: "With more people working from home, understanding what affects indoor air quality is more crucial than ever. Our methods allowed us to accurately model PM levels at a low cost, improving exposure estimates."

Researchers identified five key contributors to indoor PM: two linked to indoor activities, such as movement by residents, and three related to external sources, including a nearby restaurant`s kitchen vent. They also found that larger particles (PM10) settled faster than smaller ones (PM1, PM2.5).

Using Non-negative Matrix Factorisation (NMF), a powerful data analysis tool, the team effectively modelled indoor PM levels. Their use of low-cost sensors provided a more detailed understanding of pollutant levels within homes.