Assessment of the benefits for improved air quality due to operation of new freeway

The California line source dispersion model and chemical mass balance model simulations with air pollutants and traffic volume field measurements were performed to compare air pollutant emission and contribution of a new freeway of 37.6 km in length, before and after operation. The simulations of two models demonstrated that the concentration of four air pollutants decreased, and the average contribution to local ranges of non-methane hydrocarbons (NMHC) and PM10 from vehicle emissions changed from 49-53% in 2007 to 44-48% in 2010, and from 14-24 to 16-27%, respectively, although the freeway led to increased traffic volume to approximately 13,700 and 8,050 passenger per car equivalent daily during weekend and weekday, respectively, in 2010. The results revealed that the emission amounts of CO and NMHC decreased by 716.5 and 53.4 t yr-1, and PM10 and nitrogen oxide (NOx) increased by 5.9 and 105.5 t yr-1, respectively, between 2010 and 2008. A comparison of the data at a local and two upwind air quality monitoring stations from 2008 to 2010 revealed that local air quality had been improved after the freeway began operation. This study successfully quantified the benefits in changing air quality of a new freeway through dispersion model and receptor model simulations.