Sulphur dioxide (SO2) and particulate matter emitted from combustion of fossil fuels have, historically, been the main components of air pollution in many parts of the world.  

• A Greenpeace report from 2019 had found that India was the largest emitter of SO2 in the world due to burning of coal. 
• The EPA states that largest source of SO2 in atmosphere is burning of fossil fuels by power plants and other industrial facilities.  
• Short-term exposure to SO2 can harm respiratory system, making breathing more difficult.  

• SO2 emissions in the air can also lead to formation of other sulphur oxides (SOx), which can react with other compounds in the atmosphere and form particulate matter. 

Source: https://indianexpress.com/article/explained/explained-as-pollution-peaks-in-delhi-a-look-at-pollutants-you-should-be-worried-of-6853273/