Scientists said on Wednesday that they have solved the mystery of how a major smog component, known as sulfate, forms during heavy pollution.

The study, published in the US journal Science Advances, identified reactive nitrogen chemistry and water particles in the air as the two key elements, suggesting that reducing nitrogen oxide emissions, in particular, may help curb air pollution.

The findings were based on an analysis of heavy smog in Beijing in January 2013, one of the worst incidents of atmospheric pollution ever recorded in China, which saw the daily concentration levels of hazardous PM2.5 exceed the World Health Organization's guideline by 16 times.