Reconnaissance study of air quality in traffic tunnels: A case study of Aba-Saleh Al-Mahdi tunnel,Iran

Abstract

Traffic tunnels have the potential to reduce the traffic congestion, but in some cases, they lead to the accumulation of air pollutants. The present study focused on the analysis of chemical and biological pollutants inside and outside of the largest tunnel in Iran. The measurements were done during different hours and days in four seasons (2018–2019). The collected data showed that the inside of the tunnel was more polluted than the outside, and the type, the number of passing cars and the weather condition had an effect on concentrations. Winter, summer and evenings are the most polluted periods. Comparison of data with national and WHO standards revealed that SO₂ is a critical pollutant for all periods; NO₂ is a problem during summer, winter and evenings. The concentration of PM_2.5 exceeded these standards in the evenings. A high correlation between PM_2.5 and PM₁₀, in concentration, changes and spatial distribution points to the same emission sources. For biological pollutants, a high microbial population was found during the summer and afternoons. Among the isolated Gram-positive bacterium, the Bacillus sp (38%) and Aspergillus sp (32%) were the highest population of bacteria and fungi, respectively. Measurement results in combination with a high rate of hospital admissions emphasized the poor air quality inside the tunnel and the necessity for the installation of mechanical ventilation systems.