Air pollution disproportionately affects the poor and marginalized around the world, and India is no exception. A new study published in Scientific Reports shows that lower-caste communities and other socially disadvantaged groups have the greatest exposure in the country.
“Equity must thus be a core consideration in the development of effective air pollution mitigation plans,” said Priyanka deSouza, the first author of the study and an urban planner at the University of Colorado Denver.
Researchers created a data set of various socioeconomic factors (SES) for more than 28,000 areas in rural and urban India from the National Family and Health Survey conducted in 2015–2016.
The survey data helped the team estimate the prevalence of socioeconomically disadvantaged communities within each area. These include the officially designated communities of Scheduled Castes, Scheduled Tribes, and Other Backward Class households, as well as households of religious minorities, the poor, those lacking formal education, those without electricity, and those without access to sanitation facilities.
The researchers compared satellite-derived and estimated measurements of particulate matter smaller than 2.5 micrometers (PM2.5) among areas that had the lowest and highest proportions of disadvantaged communities. Prolonged PM2.5 exposure comes with health risks such as asthma and heart disease.
“The study does a great job of characterizing the inequalities in exposure across different socioeconomic and religious groups in a way that we perhaps intuitively knew but hadn’t empirically measured.”
The study found that mean total PM2.5 concentrations were higher on average in areas that had a high prevalence of disadvantaged communities. PM2.5 levels in areas with the lowest prevalence of people who are part of Scheduled Castes, for instance, were 21 micrograms per cubic meter on average. In areas with the highest prevalence of members of Scheduled Castes, levels reached 61 micrograms per cubic meter.
Although these higher levels are not very different from the country’s overall average PM2.5 levels (53–70 micrograms per cubic meter), they are several times higher than the World Health Organization’s recommended annual average PM2.5 concentrations of 5 micrograms per cubic meter. Studies have shown that for every 10-microgram-per-cubic-meter increase in PM2.5 exposure, PM-related mortality increases by 2.8%.
“The study does a great job of characterizing the inequalities in exposure across different socioeconomic and religious groups in a way that we perhaps intuitively knew but hadn’t empirically measured,” said Bhargav Krishna, an environmental health and policy researcher at the Sustainable Futures Collaborative in New Delhi who was not involved in the study.
Polash Mukerjee, a U.S.-based independent air quality and climate health researcher, said the data could be used to persuade decisionmakers to plan mitigation interventions around large sources of air pollution such as power plants.
Caste as a Main Determinant of Exposure
“After accounting for different levels of poverty, access to amenities, and religion, we found that PM2.5 levels were significantly higher in areas with more lower-caste residents,” said deSouza.
The distinction should be accounted for in public policy decisions affecting air quality, Mukerjee said. This could mean focusing funding for clean domestic energy on Scheduled Caste and Other Backward Class households and promoting access to preventive and curative health care for respiratory and air pollution–linked diseases, he suggested.
Rural and urban populations also experienced different exposures to PM2.5 levels, sometimes in counterintuitive ways. For example, explained deSouza, although Scheduled Tribes are a disadvantaged community, they are more likely to “live in rural, remote areas, so it is likely that their exposure [to PM2.5] is lower.”
Karn Vohra, an environmental health researcher at University College London, said India needs more PM2.5 measurements and higher-resolution data to improve understanding of the way PM2.5 levels affect local populations. He also suggested further research into indoor, as well as outdoor, air quality.
Overall, “the study shows there is a much more nuanced story to be told on the interplay between SES, development, and air pollution exposure,” Krishna said.
—Deepa Padmanaban (@deepa_padma), Science Writer