The new study, part-funded by NASA, combined satellite data with modelling to estimate levels of small particulate matter that damage health and lead to early death
Outdoor pollution is not primarily an urban problem and ambient air is as toxic in rural parts of India as in the urban regions, found a new study part-funded by NASA that combined satellite data with modelling to estimate levels of small particulate matter (PM2.5 > 2.5 μm) that damage health and lead to early death.
In the rest of India, the average PM2.5 levels are similar in rural and urban areas, found the study by researchers from the Colorado State University and Indian Institute of Technology Bombay. It found that most people in India (84% of the population) are exposed to pollution well above the limit of India’s standard (40 μg/m3 ), and almost the entire country is exposed to levels higher than the WHO standard (10 μg/m3 ), with “a long tail of very high concentrations (>160 μg/m3 ) in the urban regions in the Indo-Gangetic plains and parts of non-urban areas in eastern and western India”.
Around 16% of India’s population is not affected by this pollution (below 40 μg/m3 ), and that is mostly confined to the very north-western parts of India, the Western Ghats, and a few regions within India. The fraction that is below the WHO standards is very small (<0.001%), said the study, which has implications for air quality monitoring, regulations, public health, and policy. It was published in the journal, Proceedings of the National Academy of Sciences (PNAS) on Tuesday.
“I was a little surprised (with the results), though our previous work was indicating this. We calculated these using satellite data, so no, there are no significant gaps,” said lead author R. Ravishankara, University Distinguished Professor, Departments of Chemistry and Atmospheric Science at Colorado State University, US, in an email.
“Only the very north western part of India appears to be below the threshold for PM2.5. We have used premature mortality as the metric to measure the health impact. In addition to premature mortality, there are other negative impacts such as asthma, hospital visits, medical costs, etc,” said Ravishankaran.
The findings are in line with the State of Global Air 2020 report released in October, which said that India had recorded the highest annual average PM2.5 concentration exposure in the world in 2019, followed by Nepal, Niger, Qatar and Nigeria.
For the PNAS study, researchers calculated the annually averaged aerosol optical depth (AOD) from three satellite instruments (Methods) that were converted to surface PM2.5 abundances using PM2.5:AOD ratios from the GEOSChem chemical transport model. They then compared the satellite-derived daily and annual PM2.5 with the surface PM2.5 measured by India’s Central Pollution Control Board at 20 monitoring sites, most of which were in urban areas.
The annual premature deaths attributable to PM2.5 alone for urban and rural India is 1.05 million, found the study, which factored in six causes of death: ischemic heart disease, stroke, lower respiratory infections, chronic obstructive pulmonary disease, lung cancer, and type-2 diabetes.
Long-term exposure to outdoor and household air pollution contributed to over 1.67 million annual premature deaths from stroke, heart attack, diabetes, lung cancer, chronic lung diseases, and neonatal diseases, in India in 2019 according to State of Global Air Report 2020.
The analysis revealed that the risk of premature deaths attributable to PM2.5 is similar in rural and urban regions, but there were more deaths in rural areas as it is home to 69% of the country’s population.
“We have used premature mortality as the metric to measure the health impact. These are quantified in the paper. In addition to premature mortality, there are other negative impacts such as asthma, hospital visits, medical costs, etc,” said Ravisankaran.
The findings suggest that efforts to monitor and curtail air pollution should not be limited to India’s urban areas. Enhancing monitoring and regulation in rural areas, which are virtually non-existent, could help better assess the risks and inform policy for pan-India reduction of PM2.5 levels keeping in mind the rural populations lower ability to reduce risks because of economic reasons.
“The Global Burden of Disease 2019 shows us that possibly 100% of India is exposed to air that is not meeting the WHO guidelines, and anywhere between 69% to 85% of the population is exposed to air that doesn’t meet the national standard. Now there is a mix of satellite, chemical transport and ground monitor data to prove this. There are studies now showing that 30% to 50% of outdoor air pollution is contributed by household sources of emissions. The health impacts on both rural and urban populations could range from cardio-respiratory, cardiovascular conditions, diabetes, low birthweight, preterm birth and neonatal mortality,” said Kalpana Balakrishnan, the director of the Indian Council of Medical Research Centre for Advanced Research on Air Quality, Climate and Health, Chennai.
“My key message is: Please don’t forget non-urban India when dealing with air pollution. The second key message is: Science, measurements, and analyses can help overcome this problem with good information to the policymakers,” said Ravisankaran.