Size-resolved particle distribution and gaseous concentrations by real-world road tunnel measurement

Measurements of aerosol particle number (PN) size distributions (15-700 nm), CO and NOx were performed in a bus tunnel, Australia. Daily mean particle size distributions (PSDs) of mixed diesel/compressed natural gas (CNG) buses traffic flow were determined in four consecutive measurement days. Emission factors (EFs) of PSD of diesel buses and CNG buses were obtained by multiple linear regression (MLR) methods, particle distributions of diesel buses and CNG buses were observed as single accumulation mode and nuclei-mode separately. PSDs of mixed traffic flow were decomposed by two log-normal fitting curves for each 30-minutes interval mean scans, all the mix fleet PSD emission can be well fitted by the summation of two log-normal distribution curves, and these were composed of nuclei mode curve and accumulation curve, which were affirmed as the CNG buses and diesel buses PN emission curves, respectively. Finally, PSDs of diesel buses and CNG buses were quantified by statistical whisker-box charts. For log-normal PSD of diesel buses, accumulation mode diameters were 74.5-87.5 nm, geometric standard deviations were 1.89-1.98. As to log-normal PSD of CNG buses, nuclei-mode diameters were 21-24 nm, geometric standard deviations were 1.27-1.31.