It is often said that the world’s environmental burdens will fall on the shoulders of the poor and not the rich. In the case of Delhi’s particulate matter (PM2.5) air pollution, this statement would seem to ring true. Wealthier households are more likely to be located in quiet and leafy neighborhoods, far away from busy urban intersections. They are more likely to spend their time indoors, and not in the dusty streets outside.

Yet in Delhi, there is little information on indoor air quality levels and how they vary across socio-economic strata. According to industry reports, purchases of indoor air purifiers are rising. But is it really true that the rich are breathing clean air in Delhi? 

Between 2018 and 2020, we measured indoor air quality in thousands of Delhi homes. The households in our sample were drawn from a wide range of socio-economic groups. Some were located in Jhuggie Jhopri (J.J.) informal settlements like Shahbad and Kathputli Colony, where nearly a quarter of those we surveyed reported never enrolling in school, and weekly incomes averaged 2,000 INR. Other households were sampled from upscale colonies across South Delhi, like Vasant Kunj and New Friends Colony, where roughly 65% of those we surveyed reported graduating from college.

In nearly every neighborhood we visited, average levels of wintertime indoor air pollution exceeded the World Health Organization (WHO) PM2.5 guideline (recently revised downwards to 5 µg/m³) by a whopping 46 times. Not only that, indoor PM2.5 levels were consistently higher than those reported on the nearest outdoor government monitors. Most surprisingly, PM2.5 levels inside richer homes were just 10% lower than those found in poorer homes.

Simply put, very few in Delhi are breathing clean air.

There are a couple reasons that could explain these patterns. PM2.5 is emitted from many different sources which are unevenly distributed across the city. Although a government monitor may accurately measure PM2.5 in its immediate vicinity, the air quality can be substantially different just a 100 meters away. In the J.J. communities we studied, pollution levels at the street-level were higher than those measured inside homes and those reported on the nearest government monitor. This highlights the urgency of more widespread monitoring.

As one would expect, the higher socio-economic status (“SES”) households we surveyed were more likely to own an air purifier compared to lower SES households. Nonetheless, air purifier ownership rates were low. Despite the remarkable ability of these machines to filter nearly all pollution, less than 20% of the higher SES households in our sample reported owning one.

Our findings suggest there is low awareness of indoor air pollution in Delhi. That said, distributing air quality sensors to higher SES households did not lead to detectable increases in air purifier purchases or in other avoidance behaviors. The challenge, it would seem, is to not only make people aware, but to also make them care.

Our data highlight the importance of increasing the available information on air pollution and its health effects, both inside and outside people’s homes. None of the continuous ambient air quality monitoring stations in the National Capital Region can shed light on indoor air pollution levels at schools and workplaces. In addition, PM2.5 levels need to be communicated in a way that better emphasizes its impact on health. The stakes are high. The Air Quality Life Index (AQLI) shows that particulate pollution is the greatest risk to human health, shortening life expectancies across India by nearly six years, on average.

It’s possible that attitudes towards air pollution have changed since we conducted our study, which took place shortly before the onset of the COVID-19 pandemic. The threat of the coronavirus may have changed perceptions about the importance of addressing a similarly invisible and insidious health threat like air pollution.

History shows that the path to clean air runs through widespread awareness, which in turn, drives citizen demand for change. Greater awareness and demand will also be beneficial for the Government of India’s National Clean Air Programme (NCAP), which is targeting a 20 to 30% reduction in PM2.5 concentrations by 2024, and will require widespread public buy-in and compliance.

In Delhi, where not even the rich are breathing clean air, it is in everyone’s interest to solve this problem.