Which country has the worst air pollution? Clue: it's not China

When people think of poor air quality, images of a smoggy Beijing skyline often come to mind. China's difficulties with pollution have given it the reputation of having the worst air quality in the world.

But while China undoubtedly still has work to do, the world's second largest economy has made huge strides in improving its air quality. Last year, in the quarter ending 30 September, China was the largest centre of investment in the world for renewable energy, with $26.7 billion - twice that of the second largest, the United States. In 2014, it led the world in new clean energy, adding 56 gigawatts to the grid, four times what the US contributed.

A new study by Greenpeace shows that these investments are starting to make a difference. Using NASA satellite images to measure microscopic particles, the study found that levels of PM2.5 particles in China had decreased by 17% between 2010 and 2015. In the United States the fall was 15%.

That's great news for China, but not so much for India, where the situation has gotten worse. Annual PM2 levels in New Delhi were at 128 compared to Beijing's 81 and Washington D.C.'s 12. The study lays out recommendations for India to curb their PM2 levels, which include a pollution action plan to enforce compliance of coal-fired power plants and the institution of air quality monitoring systems in urban areas. China launched its own action plan in 2013.

Thirteen of the top 20 most polluted cities in the world, according a World Health Organization (WHO) report from 2013, are in India. This has led to fears for the health of children living in Asia’s third largest economy.

Using satellite technology to better understand the state and impact of air pollution has become increasingly valuable to climatologists. Davis Crisp, Senior Research Scientist at the Jet Propulsion Laboratory, presented the latest advancements and discoveries at the Annual Meeting of the World Champions last year.