Assessing Ambient Formaldehyde Exposure and Estimating Cancer Risks over India using the Ozone Monitoring Instrument Satellite Sensor

Estimating human exposure to formaldehyde (HCHO) is challenging due to sparse in situ measurements over India. We develop an ambient HCHO exposure data set to assess the long-term changes in exposure and to calculate the potential HCHO-related cancer risks in India. We estimate the long-term mean (2005–2019) annual 24-h average surface HCHO concentrations at a spatial resolution of 0.1° × 0.1° (latitude × longitude) over India by scaling the HCHO vertical column density retrievals from the Ozone Monitoring Instrument (OMI) satellite sensor with the atmospheric profile information from the MERRA2 GMI chemical transport model. We find an increase in long-term HCHO exposure of >0.05 ppb (parts per billion by volume) for most Indian states (2015–2019 annual mean compared to 2005–2009 mean). The OMI-based estimate shows that the Indian population of 40,000–76,000 will likely be under enhanced cancer risk due to exposure to long-term ambient HCHO. We find highest HCHO exposure values for rural regions compared to urban areas in most Indian states except Delhi national capital region. This study shows that HCHO pollution in India is a regional-centric issue. Therefore, emission mitigation policies should focus on reducing HCHO in both urban and rural regions.