India and China had the largest number of deaths owing to particulate matter (PM2.5) — small pollutant particles of 2.5 micron size that can easily enter the respiratory system and cause ailments — according to a Lancet study released on Monday. The study said 52% of the deaths that year were from these two countries.

China had the highest number of deaths in the world at 1108, followed by India that reported 1,090 deaths.

The annual safe limit for PM2.5 pollutant is 10 microgrammes per cubic metre (µg/m3), according to the World Health Organisation (WHO). The estimated average PM2.5 concentration for population-weighted exposure increased from 59 in 1990 to 73 µg/m3 in 2015 in India, which is almost four times the safe limit. The highest average exposure to PM2.5 concentration globally was seen at Qatar at 107.3 µg/m3, the report said.

India, Pakistan and Bangladesh had the highest age-adjusted (a way to make fairer comparisons between groups with different age distributions) mortality rates, too — more than seven times higher than those of Japan and the USA, according to the study.

Global mortality owing to ambient PM2.5 pollution has also increased from 1990 to 2015. Globally, attributable deaths rose from 3.5 million in 1990 to 3.8 million in 2000, and 4.2 million in 2015.

India ranked the second-highest in the world — 133.5 deaths per 1,00,000 people in 2015. Pakistan, one the other hand, came in first with 136.3 deaths per 1,00,000 people in 2015.

“In India, China, Bangladesh, and Japan, an increase in PM2.5 exposure combined with an increase in population growth and ageing resulted in a net increase in attributable mortality,” read the study. “Exposure to ambient air pollution increases morbidity and mortality, and is a leading contributor to global disease burden. We explored spatial and temporal trends in mortality and burden of disease attributable to ambient air pollution from 1990 to 2015 at global, regional, and country levels.”

Additionally, the study found exposure to ozone-pollutants emitted by vehicles, power plants, industrial boilers, refineries, chemical plants that react chemically in the presence of sunlight, contributed to 2,54,000 deaths globally. In 2015, exposure to ozone contributed to an estimated 8% of global COPD mortality in 2015, with China, India, and the USA experiencing some of the highest mortality rates.

‘India needs to reduce air pollution exposure by 20% by 2030’

The Lancent study estimated that air pollution levels in 2030 in India would need to decline by 20%, to maintain per-person mortality (measure of number of deaths in the population) at 2010 levels

The study concluded that ambient air pollution contributed substantially to the global burden of disease in 2015, which increased over the past 25 years, due to population ageing, changes in non-communicable disease rates, and increasing air pollution in low-income and middle-income countries.

“Modest reductions in burden will occur in the most polluted countries unless PM2.5 values are decreased substantially, but there is potential for substantial health benefits from exposure reduction,” read the study.