Breathing Easy? How Lockdowns Changed Indoor Air Quality in Auckland Homes

Good air quality in homes is critical for a healthy and comfortable environment. Particles that pollute the air can either come from the outside, for example from the traffic on nearby roads, or from activities in the home, such as cleaning or cooking. To ensure good air quality it is important to know where the main contributions to indoor air pollution come from (Figure 1). Should I open the windows whenever I can to let in fresh air or is that air bringing in more trouble? While this varies depending on where one lives (for example next to a major road or in a quiet street) and the construction of the house some general information could be gained as an unexpected side effect from Auckland’s first Covid-19 lockdown.

Figure 1 - Sources of Air Pollution

Understanding Indoor Air Quality

Good air quality inside homes is essential for health. Polluted indoor air can worsen conditions like asthma and allergies. Studies show we spend more time indoors these days, so keeping the air clean inside is crucial. Normally, ventilation helps remove indoor pollutants, but when windows stay shut, especially during winter to keep the home warm, these pollutants build up, making air quality worse. Mechanical ventilation systems can help by bringing in fresh air and removing stale air. Other major factors affecting Indoor air quality have been summarised in Figure 2.

Figure 2 - Major Factors Affecting Indoor Air Quality

When everyday live suddenly changes

During the COVID-19 lockdown, people spent a lot more time at home than normally, which affected the indoor air quality (IAQ) of many houses. When Auckland went into lockdown, we coincidently had already a long-term indoor air quality study underway with air quality sensors placed in homes that allowed us to compare the air quality before and after lockdown.  While being locked down at home ourselves we were able to observe the data streams from the sensors and answer what happens when people stop driving around so much and instead end up spending nearly all of their time at home.

How the Study Worked

Our research monitored six homes in Auckland with mechanical ventilation systems, each with three to four bedrooms. The study compared air quality data from three weeks before lockdown and three weeks during lockdown. Indoor monitors measured PM2.5 and PM10 , that is fine and larger particles, aka “dust”,  in bedrooms and living rooms, while outdoor data came from nearby council air quality stations. The sensors used were calibrated for accuracy, ensuring the data was reliable.

 What Happened to Air Quality?

All the homes before the lockdown were usually empty during the day (working hours). Once lockdown began, occupancy went up, and the homes stayed occupied all day. During the lockdown, PM2.5 and PM10  levels went up indoors in most homes, while outdoor levels dropped. This shows that indoor sources like cooking, cleaning, or using heaters were the main cause of higher particle levels.

Indoor vs. Outdoor Air Quality

While mechanical systems were working for much longer periods during the day, indoor PM2.5 levels still increased on average by 55% in homes during the lockdown. PM10 levels also rose in around 50% of the homes, suggesting that most of the particle sources were inside.

Outdoor air quality improved during lockdown as traffic and industrial activity decreased, cutting down outdoor PM2.5 by around 33% and PM10 by around 30%.

Comparing indoor and outdoor air quality showed that while outdoor levels went down, the air inside worsened due to an increase in indoor activities, showing that sources inside the home were the main contributors during lockdown.

What to do?

Mechanical ventilation did help reduce indoor pollutants, but it couldn’t fully control the rise in indoor-generated particles due to the greatly increased activity at home. As we didn’t have sensors in any houses without mechanical ventilation systems and we can’t nor would we want to repeat a lockdown, we can’t tell how big the difference between mechanically ventilated and unventilated houses would have been but given that so much of the air pollution came from inside the house more ventilation logically must have helped. This emphasizes that good ventilation is critical for a healthy home with the best method of ventilation dependent on location, layout of the house, behaviour of the inhabitants and the budget available.

If you have any questions for the team that you would like answered in this column, please contact us.\

This research was provided by our Senior Air Quality Analyst, German Hernandez, who is currently completing his PhD at the Universidad Politécnica de Madrid.