There has been a lot of talk and innovation in ways to move ourselves around a city while polluting less, but we must keep in mind that won't solve all of our air quality problems.
To achieve the air quality improvements that were experienced during the 2008 Olympic games, Beijing had to shut down 150 heavily polluting chemical engineering and cement factories, in addition to reducing government vehicle use by 70%. In other places, the wind can be relied upon to disperse the pollution instead of allowing it to build up, but Beijing is near a mountain range that traps it’s pollution, plus pollution from neighboring regions during certain times of the year.
The road from the mountains down into Beijing in the winter:
Image source: http://4.bp.blogspot.com/-A4Q6u7xwO1E/TuIuIzAWqsI/AAAAAAAABUA/62UzYjhPRN4/s1600/UtahValleySmog26Jan07.jpg
Not all of the air pollution is man-made. Beijing is hit with a yellow haze of sand that blows in from storms around Inner Mongolia, up to a couple hundred miles away. (There are also manmade sources of PM 2.5 such as diesel combustion, and smoke of all kinds) The finest dust gets carried the farthest, and it is the tiniest particles that cause the greatest harm to lungs. PM 2.5 stands for “particulate matter, 2.5 micrometers” which penetrates deep into the cilia in lungs where they irritate the tissue, and are not easily coughed up or removed. Exposure to PM 2.5 leads to high plaque deposits in arteries, causing vascular inflammation and atherosclerosis. While no one can prevent the introduction of dust from storms, it can be mitigated slightly by street sweeping and washing. As the dust settles onto the road and cars drive over it, it can get ground even finer, and re-suspended.
Ozone is another product of combustion that Beijing is “importing” from the surrounding region – 35-60% comes from Hebei and Shandong Provinces and the Tianjin Municipality. Beijing cannot control that, but has taken steps to eliminate it’s contribution to the ozone problem by limiting personal driving by capping the cars that can be registered, and allowing them to only be driven every-other-day, and switching bus fleets to electric and natural gas buses.