However, the unburned poisons that are pumped out by car exhausts combine with oxygen to form ozone, which is lighter than air and drifts upwards to collect in the sky under an altitude of 1,000 meters. "High-rises of more than 20 storeys thus have a serious ozone problem," he warns.
然而地面上汽車所排放出燃燒不完全的廢氣，與氧氣結合成臭氧，它比空氣輕，會向上飄浮，並聚在高度一千公尺以下的低空，「廿層以上高度的樓房，臭氧問題就很嚴重了」，他警告說。