The hidden danger: How indoor air pollution mirrors outdoor threats

People like to think of their home as a place of safety — a shelter or sanctuary from many harms that they face outside. In all fairness, that is a reasonable expectation.

Commuting and working every day is tedious, competitive, and uncertain — tinged with threats like huge traffic jams, untimely heatwaves, inconsiderate rain or even muggers from a blind alley. 

Returning home provides a break from all this and lets you relax and replenish for the next day. But what if we told you that your home cannot eliminate all the threats that are outside — in fact, it provides little protection against a perilous threat that can have serious consequences for your health?

If you are a resident of Dhaka, Delhi, or Lahore, you may already know that you are living in an air pollution hotspot. According to IQAir, Dhaka's average pollution level in 2023 was 16 times higher than the WHO recommendation, and according to the Air Quality Life Index, air quality in Dhaka is so bad that it reduces life expectancy among its population by 5.6 years. 

However, it is less known that indoor air pollution is almost as bad as outdoor air quality, although the pollution is less visible indoors. In fact, most of the air pollution from outdoors seeps into our homes through windows, doors, and ventilation systems, making indoor air pollution almost as bad as that outside.

As part of a recent study during the highly polluted winter months, we asked a series of questions regarding air pollution to a thousand households in Mirpur — a populous, middle-class neighbourhood in the heart of Dhaka. When we asked them about the outdoor air quality, the responses were understandably pessimistic. 

Some 76% of households responded that they believe that the outdoor air in their area is severely polluted. However, people are unaware that indoor air pollution is bad, with only 24% of respondents stating that the air quality within their homes is severely polluted. 

So, among our respondents, we can see that when people think about air pollution, they largely think of it as an outdoor problem that can be effectively negated once they are inside their homes.

We measured the veracity of this belief by placing indoor air monitors inside the homes of 500 of our study participants. Furthermore, we placed two outdoor air pollution monitors on rooftops in the areas that we studied. We found that indoor air pollution is, on average, 77% of outdoor air pollution. 

This means that the vast majority of (three-quarters) of the outdoor air pollution also enters our homes, even in middle-class apartment buildings that are better sealed from outdoor pollution than simpler houses. This means indoor air quality in Dhaka is unhealthy and can even be hazardous. If you are living in Dhaka, there is no reason to think that getting inside your home will provide a safe refuge.

We also asked households what their beliefs are about the share of air pollution that enters their homes. The average belief was that the air pollution inside their home was just 43% of the outdoor air pollution. 

This means that, on average, people underestimate the amount of air pollution inside their own homes and believe that it is almost half of what it actually is. This is not surprising since it is not possible to see indoor air pollution; you need a monitor to measure it.

The lack of understanding about the level of indoor air pollution has direct negative consequences. The first is that families do not take appropriate measures to protect themselves from indoor air pollution. 

For example, we found that less than 1% of the households owned an air purifier and that even among households that owned air purifiers, they rarely used them. Furthermore, households may feel as if they are protected from air pollution for most of the day, and therefore, they do not think of reducing air pollution as something that should be a top priority on the government's agenda.

Our research shows that air pollution is a large problem, even inside of our own homes. This is a fact that needs to be made clear to the population so that we can protect ourselves and our families by using technologies such as air purifiers.

Martin Mattsson is an Assistant Professor at the National University of Singapore, Teevrat Garg is an Associate Professor at the University of California, San Diego, Maulik Jagnani is an Assistant Professor at TUFTS University, and Ashfaqul Haq is a Senior Country Economist at the International Growth Center.

Disclaimer: The views and opinions expressed in this article are those of the authors and do not necessarily reflect the opinions and views of The Business Standard.