What Step Is Crucial in Fighting Cities' Air Pollution?

In rapidly growing cities such as Beijing and New Delhi, air pollution has become so severe that respiratory disease is on the rise, flights have been grounded, and the public is often warned against letting children play outside.

Chokingly thick blankets of smog are often a byproduct of economic growth, which results in more vehicles on the road and more burning of fossil fuels, especially coal. The bad air can be deadly: Outdoor air pollution, both in cities and rural areas, prematurely killed 3.7 million people worldwide in 2012, according to the World Health Organization. With two-thirds of the population expected to live in cities by 2050, the need to ease urban pollution is particularly acute.

The problem goes beyond respiratory health and quality of life: A recent study published in the Proceedings of the National Academy of Sciences found that in India, short-lived air pollutants such as ozone and black carbon, along with the changing climate, cut 2010 crop yields in half.

Los Angeles offers an example of what cities can do to reduce pollution. Long notorious for its smog, the car-centric city has seen some air pollutants decline by 98 percent over the past 50 years, even though an increasing population has used more gasoline. Rules to make cars and fuels cleaner helped achieve the reductions, but the city still struggles with air quality issues. In 2014, Los Angeles saw an uptick in smog due to heat and drought, suggesting the fight against air pollution remains a challenge for cities dealing with both climate change and population growth.

In the drive to build smarter cities around the world, what is the most important thing we should do to tackle air pollution?

Give your rating for the answers below and share your thoughts in the comments.