In 2019-20, Delhi’s air had an average of 216 micrograms per cubic metre (μg/m³) of PM2.5 pollutants during the stubble-burning phase from mid-October to mid-November. The peak winter was hardly better, with PM2.5 levels of 201 μg/m³ from mid-December to mid-January. In the two prior years, this period, when biomass burning is at its zenith, had even dirtier air than the stubble burning period.

Yet, this issue gets overshadowed by the politically-charged chatter around crop burning. The latter was mentioned the most often (31 out of 109) in Lok Sabha questions about air pollution between 2016 and 2019. Household biomass burning was mentioned just 12 times, shows a new working paper from Delhi-based think tank Centre for Policy Research (CPR).

“Crop burning gets so much attention because it’s a very visible source, with a conspicuous impact on pollution during end-October to mid-November,” said Santosh Harish, the lead researcher. “Household sources are relatively invisible, and have existed forever.”

Biomass burning by households for cooking and heating needs in winters is the main culprit, responsible for up to 40% air pollution in this period in the National Capital Region (NCR), research shows. Its share in PM2.5 levels goes up as stubble burning ebbs.

Fatal air

But the problem of indoor pollution is not limited to the NCR and winter alone. Various databases find its share in India’s total annual PM2.5 emissions at between 27% and 49%, far more than any other source.

This kills around 600,000 Indians prematurely every year, by far the most for a country, according to the Global Burden of Disease Study 2019. Women, children and the elderly who stay longer at home are at greater risk. Household air pollution causes 36% of all deaths due to air pollution.

In Delhi’s poorest homes, PM2.5 levels are 23 times the safe limit, found another recent study by the Energy Policy Institute at the University of Chicago. Indoor pollution spikes during mornings and evenings when households are most likely to be cooking, the study said .

Such findings are at odds with recent executive decisions to shut schools and keep children at home to protect them from bad air.

Energy poverty

Cooking accounts for a bulk of the indoor PM2.5 emissions, up to 60% by a 2018 report by Health Effects Institute (HEI), Boston. This is not surprising: the 2019-21 National Family Health Survey counted 41% households in India, mainly in rural areas and poorer eastern states, who still don’t use clean fuel for cooking, despite close to universal coverage of the Ujjwala scheme.

Not surprisingly, states lagging on clean cooking such as Bihar, Meghalaya, West Bengal, Uttar Pradesh and Assam also see greater contribution of domestic biomass towards PM2.5 emissions, said the HEI report.

The first step is to acknowledge that access alone cannot ensure clean fuel use, as a survey of urban slums by the Council on Energy, Environment and Water (CEEW) found. Nearly 88% of households surveyed in energy-poor states reported having an LPG connection, but only 55% exclusively used it for cooking.

Winter effects

Delhi reported a high clean fuel penetration (99%), yet the city becomes the epicenter of pollution in winters. This is because in the coldest weeks, space heating in poorer households remains dependent on biomass, which lifts pollution levels, said Harish. With firewood already available for such purposes, households may prefer to then use it for cooking, too, said Sasmita Patnaik, a researcher who was part of the CEEW study. Almost all households with LPG covered in the survey used it during monsoons, but not as much during winters.

“Despite having LPG, people tend to use solid fuel as it’s more easily available. We need more awareness about the health implications…and behavioural change towards sustainable heating methods such as LPG or electricity,” said Pratima Singh, a research scientist at Center for Study of Science, Technology and Policy.

What this shows is that air pollution is not just an environmental problem but linked to larger developmental challenges. Beijing curbed 17% of its pollution by transitioning to clean energy in residential spaces. India can, too.