What are the effects of air pollution in cities during the night?
Ash, this is an excellent question and a study conducted in Phoenix, Arizona during the Summer of 2001 discusses this topic. Hence, “The data show that cooler nighttime temperatures trap auto emissions from early morning commuters and other pollutants in a shallow layer close to the ground in the Phoenix basin. When the sun comes up and warms the ground, vertical mixing becomes vigorous in a growing layer near the surface and the pollutants are quickly mixed upward throughout this layer. Concentrations of ozone at approximately 6,000 feet above ground were as much as (or more than) 50% higher than those found at lower elevations during the morning hours. On a number of days, the observed rate of increase in ozone appeared to be related to the period of time that vertical mixing became well developed, providing evidence of a close link between chemical processes and the onset of mixing.” Therefore, air pollution at night remains close to the ground. But, when the sun rises and heats the
