PM10 non-exhaust emission factors from tunnel measurements using a novel approach accounting for deposition and resuspension

An improved understanding of PM non-exhaust sources from abrasion and resuspension processes is important for ambient air quality management and tunnel air management. Traffic tunnels are often used for real world air pollutant emission measurements. In contrast to ambient air quality measurements, flow and dilution conditions are well defined, driven speeds are typically constant. Data from two monitoring campaigns in a 10 km long tunnel with different distances between the air quality monitoring stations (3380 m/7180 m) have been re-analysed. The objective was to study the role of traffic volume on emission factors and to examine if PM10 deposition as opposed to resuspension needs consideration in road tunnel emission measurements. Without accounting for potential prevailing deposition processes non-exhaust emission factors evaluated from concentration gradient measurements in long road tunnels approach 0 or are even negative. Non-exhaust emission factors were significantly increased by using an effective deposition velocity as a sink term accounting for the interplay of wall deposition losses and resuspension of PM10. Average light vehicle (LV) PM10 non-exhaust EF ranged between 0.015 g/km/LV (35000 LV/day) to 0.060 g/km/LV (6500 LV/day). Average heavy duty vehicle (HV) PM10 non-exhaust EF ranged between 0.080 g/km/HV (6000 HV/day) to 0.300 g/km/HV (1500 HV/day).