Dynamics of ultrafine particles inside a roadway tunnel
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Size-segregated ultrafine particles from motor vehicles were investigated in the Craeybeckx tunnel (E19 motorway, Antwerp, Belgium) at two measurement sites, at 100 and 300 m inside the tunnel, respectively, during March 2008. It was observed that out of the three size modes, nucleation, Aitken, and accumulation, Aitken mode was the most dominant size fraction inside the tunnel. The diurnal variation in ultrafine particle (UFP) levels closely follows the vehicular traffic inside the tunnel, which was maximum during office rush hours, both in the morning and evening and minimum during night-time around 3 am. The tunnel data showed very high growth rates in comparison with free atmosphere. The average condensation sink during the growth period was 14.1–17.3 × 10−2 s−1. The average growth rate (GR) of geometric mean diameter was found to be 18.6 ± 2.45 nm h−1. It was observed that increase in Aitken mode was related to the numbers of heavy-duty vehicles (HDV), as they emit mainly in the Aitken mode. The higher Aitken mode during traffic jams correlated well with HDV numbers. At the end of the tunnel, sudden dilution leading to fast coagulation was responsible for the sudden drop in the UFP number concentration.
KeywordsTunnel measurements UFP Vehicular traffic SMPS Aitken mode
The authors acknowledge the logistical support during the entire sampling period and traffic count data provided by the Flemish traffic department and Craeybeckx tunnel authority. Part of this research was supported by the Belgian Federal Science policy in the SHAPES project under the SSD program. The authors also acknowledge the academic and infrastructural support provided by the Shriram Institute For Industrial Research, Delhi, India. Especially to the Director, Dr. K.M. Chacko, and Deputy Director, Dr. M.L. Aggarwal for their valuable support.
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