American pollution does not come from factories anymore, it comes from tailpipes, and the amount that people are driving in your city, your urban VMT, is a good prediction of the asthma problems in your city.
美国的污染来源不再是工厂 而是来自于汽车的排气管 你的城市中开车的人数 以及车辆行驶里程能够很好的 推测你的城市的哮喘问题