Household air pollution from solid fuels and its invisible solution

When we think of air pollution, the smoggy outdoor haze of metropolitan cities comes to mind. With India being home to 21 out of 30 of the world’s most polluted cities, the visualization as an outdoor phenomenon is not completely wrong. The ambient concentration of particulate matter 2.5 (PM2.5 particles that have an aerodynamic diameter less than 2.5 micrometers, 20-30 times less than the size of a single strand of human hair) in our cities is far more than the World Health Organization (WHO) guideline of 10µg/m3 as well as that of the Central Pollution Control Board (CPCB) Standard 40µg/m3. As a result, we prefer staying indoors in the safety of controlled environments to protect ourselves from this health hazard. However, many of us are unaware that the level of indoor air pollution in majority of Indian households is far worse than the outdoor ambient air pollution one. I compared outdoor air pollution and indoor air pollution concertation data and found that indoor PM2.5 level in most Indian households is 2-13 times higher than the outdoor PM2.5 concentration of the respective geographic areas.

On an average, the Indian population spends 80% of their time in an indoor environment. The PM2.5 concentration in majority of Indian households ranges from 86-882 µg/m3. A higher PM2.5 concentration in a closed environment is ten times more harmful than a similar outdoor concentration because contained areas enable potential pollutants to build up more than open spaces do.

There are several sources of indoor air pollution. These include smoke from fuel burned for heating and cooking, smoke from tobacco, building materials (paints, varnishes, wood flooring, etc.), adhesives in furniture and electronics, broken CFLs and tube lights, excess moisture, and overall outdoor air pollution. Out of these sources, burning solid fuel for cooking is the leading source of indoor air pollution in India. According to a recent Global Burden of Disease estimation, solid fuel burned for coking accounted for six lakh premature deaths in 2019 in India. Our assessments of latest available data from the 2011 Census, Census of India Projected Population 2019 and  Indicators of Social Consumption suggests that 36% of the total Indian population uses solid fuels (firewood, crop residue, cow dung cake, coal, lignite and charcoal) and kerosene as primary cooking fuel as of 2020. The use of solid fuels and kerosene as primary cooking fuels is much higher in rural areas (51%) than in urban areas (9%).

There is a decrease in the use of solid fuels as primary cooking fuel in India because of rising income and the implementation of policies like Prime Minister Ujjwala Yojana. In the recent estimation by Global Burden of Disease, it is still ranked sixth among the top risk factors for premature mortalities in India. A deeper analysis of the latest available microdata of National Sample Survey, Access to Clean Cooking Energy and Electricity and Indicators of Social Consumption indicates that 77% of the Indian population uses solid fuels for cooking either as primary or secondary fuel, much higher than primary solid fuel use data of 36%. This means that current studies might be underestimating the number of premature mortalities associated with indoor air pollution. The analysis indicates that many LPG users also use solid fuels for cooking as a secondary fuel. However, there is no or limited direct data available for secondary fuel use by LPG users; therefore, many-a-times, we only consider primary fuel data for scientific studies and policymaking. There are several reasons for the use of secondary solid fuel use by LPG users that includes economic, accessibility of LPG, social, and behavioral reasons. This shows that scientific and policymaking communities need to strongly consider this invisible data of secondary use of solid fuels by LPG users while framing India's indoor pollution policies.

Giving more attention to indoor air can benefit both indoor and outdoor air pollution in since using solid fuel for cooking is also a major cause of outdoor air pollution in India. Besides improving outdoor and indoor air quality by focusing on clean cooking fuel for households would also give other co-benefits such as empowering women and protecting children. Conducting mass awareness programs for secondary solid fuel users who already own an LPG connection can reduce indoor air pollution and associated emissions of 41% of households (secondary fuel user) out of a total of 77% (primary and secondary) solid fuel users. This is a low hanging fruit which will reduce both indoor and outdoor air pollution, however not much is being done in this direction.