India, Russia, and China were the top global emitters of sulfur dioxide — a key pollutant and contributor to deaths from air pollution globally.

A new Greenpeace analysis looked at NASA data on sources of sulfur dioxide and ranked hotspots and countries by their emissions in 2018.

The main sources of sulfur dioxide — or SO2 — are power plants burning fossil fuels such as oil and gas, while other sources include metal smelters and volcanoes. Ships and other vehicles that burn sulfur also release SO2.

“The burning of fossil fuels such as coal, oil and gas is the largest source of emissions of SO2 resulting in disastrous air pollution and premature deaths. Clean energy could save billions of dollars in health costs and thousands of lives every year," said Lauri Myllyvirta, a senior analyst at Greenpeace Nordic.

"It’s fundamental that governments rapidly transition away from fossil fuels and set stronger emission standards as they shift over to sustainable alternatives.”

The analysis found that India was the top emitter of SO2 in 2018 and made up 15% of global emissions. The country recently surpassed Russia and China.

China and the United States, meanwhile, have reduced emissions rapidly by switching to clean energy sources, Greenpeace said, though both are still within the top ten country emitters.

The report also ranked hotspot regions, of which the top emitter was Norilsk, Russia, which emitted more SO2 per year than Saudi Arabia.

Norilsk smelters "are responsible for more than 50% of the total emissions tracked by NASA in the whole of Russia," the report said. The industrial city is located at the foot of a mountain range in Siberia that has large nickel deposits.

Kriel, South Africa was the second-largest hotspot for SO2 emissions due to its coal-fired power plants, and another area with a coal-fired power plant in South Africa ranked seventh globally for sulfur dioxide.

The 12 coal-fired power stations in South Africa's Mpumalanga region make it the largest hotspot in the world for power generation, Greenpeace said.

In most of those cities, the major source of SO2 emissions is coal, oil, or gas.

The World Health Organization estimates that 4.2 million people die yearly as a result of outdoor air pollution and that 91% of the world's population lives in areas where "air quality exceeds WHO guideline limits".

As part of the report, Greenpeace created an interactive map that shows the hotspots and different contributors to SO2 pollution.