Exterior air quality monitoring for the Eurasia Tunnel in Istanbul, Turkey.

Traffic is a major concern for the city of Istanbul due to the rapid increase in population and car ownership. Eurasia Tunnel, which has a capacity around 100,000 light vehicles/day, is the fourth highway link between Asia and Europe, established to relieve the existing pressure on the transport system. As an important alternative to other Bosphorus Strait crossings, the tunnel offers directly reduced traffic durations in the city especially during rush hours and indirectly provides reduced fuel consumption, thereby less harmful gas emissions into the atmosphere. The main objective of this study is to evaluate the air quality effects of the Eurasia Tunnel on the city of Istanbul through investigating the air quality 1 year before and 2 years after operation, and comparing the hourly and daily pollutant levels with tunnel traffic. Monitoring data were examined to detect the relationships between selected pollutant concentrations, to evaluate meteorology effects on the pollutants and to identify air quality impact of the Eurasia Tunnel. Analyses revealed that air pollutants concentrations do not increase with increase in tunnel traffic. Moreover, since the tunnel entered operation, average hourly CO, PM and PM concentrations at monitoring stations located close to the stacks have decreased 16-30%, 44-46% and 12-24%, respectively. Average NO concentrations increased about 9-24%, but these concentrations still remain below the 1-hour standard. All in all, Eurasia Tunnel has no significant effect on the Istanbul's air quality.