Many people assume that staying indoors protects them from air pollution, but recent research suggests otherwise. A new study from the University of Birmingham reveals that air pollution levels inside homes can be higher—and more unpredictable—than those outside, even when outdoor air quality is good.

Researchers conducted a two-week experiment using low-cost sensors to track particulate matter (PM) in three different households. They found that pollution levels inside varied significantly between homes, with one property exceeding the World Health Organization’s (WHO) 24-hour PM2.5 limit on nine different days. The findings emphasize the need for targeted indoor air monitoring rather than relying solely on general outdoor air quality reports.

The Sources of Indoor Pollution

The study identified five key contributors to poor indoor air quality:

1. Indoor Activities: Movement by occupants and activities like cooking, cleaning, and burning candles contributed to elevated PM levels.
2. External Factors: Nearby pollution sources, such as restaurant kitchen vents or traffic, infiltrated indoor spaces.
3. Ventilation and Airflow: Poor ventilation trapped pollutants inside, preventing them from dispersing.
4. Household Location: Homes in urban areas or near industrial zones experienced higher exposure to external pollutants.
5. Occupancy Patterns: More time spent indoors increased exposure, making indoor air quality particularly crucial for remote workers, young children, and the elderly.

Co-author and Clean Air Fellow Catrin Rathbone stressed the importance of individualized monitoring: “PM levels varied significantly between homes, indicating that monitoring just one location isn’t enough.”

The Health Risks of Indoor Pollution

Fine particulate matter (PM2.5) is particularly concerning because it can penetrate deep into the lungs and enter the bloodstream, increasing the risk of respiratory and cardiovascular diseases. Short-term exposure can cause irritation, while long-term exposure has been linked to serious health conditions like asthma, lung disease, and even cognitive decline.

Steps to Improve Indoor Air Quality

Given the findings, experts recommend several strategies to minimize indoor air pollution:

1. Improve Ventilation: Open windows regularly or use air purifiers with HEPA filters to reduce pollutant buildup.
2. Monitor Air Quality: Invest in low-cost sensors to track indoor pollution levels in real-time.
3. Reduce Indoor Pollutants: Avoid burning candles or using chemical-laden cleaning products, and opt for electric over gas stoves where possible.
4. Be Mindful of External Sources: If living near a busy road or restaurant, consider sealing windows or using air filters to limit outdoor pollution infiltration.

With remote work becoming increasingly common, the need for clean indoor air has never been greater. As study co-author Owain Rose put it: “Understanding the factors that affect air quality within households is increasingly important.” The research underscores the importance of personalized air quality assessments, ensuring that indoor spaces remain safe and healthy environments.

Advanced Techniques for Monitoring Indoor Air Quality

The study, conducted by researchers at the University of Birmingham, examined three homes located 4 km southwest of the city center. Each household had four to five occupants and relied on gas central heating and gas-fired cooking appliances. Despite these similarities, pollution levels varied significantly between the homes, highlighting the complex nature of indoor air quality.

To analyze the data, the research team utilized Non-negative Matrix Factorization (NMF)—a powerful technique for identifying hidden patterns in complex datasets. This advanced method allowed them to model indoor particulate matter (PM) levels with greater accuracy than ever before. Additionally, by using low-cost sensors, the researchers created a detailed picture of pollutant levels, paving the way for a more accessible approach to air quality monitoring.

Professor Francis Pope, co-author of the study, emphasized the significance of this research:

“Our approach is easily scalable due to its low cost and could enable air quality management in homes across Britain and beyond. This could lead to more accurate pollution exposure models and better-informed public health policies.”

The Future of Clean Air Research

The success of this study is part of a larger effort to improve air quality and public health. The Clean Air Fund, a key partner in the research, has played a crucial role in supporting this work. Imogen Martineau from the organization praised the contributions of Clean Air Fellows Owain Rose and Catrin Rathbone, stating:

“Owain and Catrin have been amazing ambassadors, and it is great to see them continuing their clean air journeys through taking jobs with leading environmental consultancies that specialize in air quality.”

The University of Birmingham remains at the forefront of air pollution research, boasting a team of over 100 researchers dedicated to studying clean air across multiple disciplines. With state-of-the-art facilities and a track record of influential studies, the university continues to shape the future of air quality science—both in the UK and worldwide.

This groundbreaking research underscores the importance of personalized indoor air quality assessments, providing a scalable solution that could revolutionize air pollution management in homes across the globe.