Start with the pollution most cities have, nitrogen oxides and hydrocarbons from tailpipe emissions and smokestack pollutants, mix in the heat and sunlight, and you get ozone.

• 而制造污染的是汽车尾气和烟囱排出的氮氧化合物和氮氢化合物，它们在高温和阳光下混合，就会产生臭氧。