AIR QUALITY AND POLLUTION FROM MOBILE SOURCES
One of the challenges for policymakers in China is that air quality monitoringdata in Chinese cities are limited，especially in high traffic areas.Based onthe available data，however，it is clear that national NOx air quality standardsare currently exceeded across large areas ，including，but not limited to，hightraffic areas.Before 1992，the annual average concentration of NOx in Shanghaiwas lower than 0.05mg/m3，which complies with the Class II air quality standardsin the People ‘s Republic of China （PRC ）。But since 1995，the NOx concentrationin Shanghai has increased slowly，from 0.051mg/m3in 1995to 0.059mg/m3in 1997.6
In Beijing，NOx concentrations within the Second Ring Road that encircles thecity center increased from 99mg/m3in 1986to 205mg/m3in 1997，more than doublingin a decade.Moreover ，carbon monoxide（CO）and NOx concentrations on Beijing‘s trunk traffic roads and interchanges exceed national environmental quality standardsall year round.7Recent data also indicate that standards for ozone ，formed bythe photochemical reaction of NOx and hydrocarbons（HC），have been exceeded inseveral metropolitan areas during the last decade.On average ，mobile sourcesare curre
