Aerosol and NO<sub>x</sub> emission factors and submicron particle number size distributions in two road tunnels with different traffic regimes

Abstract

Abstract. Measurements of aerosol particle number size distributions (18–700 nm), mass concentrations (PM2.5 and PM10) and NOx were performed in the Plabutsch tunnel, Austria, and in the Kingsway tunnel, United Kingdom. These two tunnels show different characteristics regarding the roadway gradient, the composition of the vehicle fleet and the traffic frequency. The submicron particle size distributions contained a soot mode in the diameter range D=80–100 nm and a nucleation mode in the range of D=20–40 nm. In the Kingsway tunnel with a significantly lower particle number and volume concentration level than in the Plabutsch tunnel, a clear diurnal variation of nucleation and soot mode particles correlated to the traffic density was observed. In the Plabutsch tunnel, soot mode particles also revealed a diurnal variation, whereas no substantial variation was found for the nucleation mode particles. During the night a higher number concentration of nucleation mode particles were measured than soot mode particles and vice versa during the day. In this tunnel with very high soot emissions during daytime due to the heavy-duty vehicle (HDV) share of 18% and another 40% of diesel driven light-duty vehicles (LDV) semivolatile species condense on the pre-existing soot surface area rather than forming new particles by homogeneous nucleation. With the low concentration of soot mode particles in the Kingsway tunnel, also the nucleation mode particles exhibit a diurnal variation. From the measured parameters real-world traffic emission factors were estimated for the whole vehicle fleet as well as differentiated into the two categories LDV and HDV. In the particle size range D=18–700 nm, each vehicle of the mixed fleet emits (1.50±0.08)·1014 particles km−1 (Plabutsch) and (1.26±0.10)·1014 particles km-1 (Kingsway), while particle volume emission factors of 0.209±0.008 cm3 km−1 and 0.036±0.004 cm3 km−1, respectively, were obtained. PM1 emission factors of 104±4 mg km−1 (Plabutsch) and 41±4 mg km−1 (Kingsway) were calculated. Emission factors determined in this work were in good agreement with results from other studies.

Particle number, particle mass and NO<sub>x</sub> emission factors at a highway and an urban street in Copenhagen

“…It is obvious that the emission factors of PN 0.05 that includes the major part of total particle number emissions are in good agreement with results reported by others (Imhof et al, 2006 andYli-Tuomi et al, 2005). These authors also estimated emission factors of particle number in various size ranges under real-world conditions.…”

Winter and summer time size distributions and densities of traffic-related aerosol particles at a busy highway in Helsinki

“…The geometric standard deviation (GSD) value for the nucleation mode was 1.7 both for the summer and winter. Imhof et al (2005b) measured particle size distributions in two different road tunnels in Graz and Liverpool. They found nucleation mode with GMDs around 15-20 nm in Graz and 25 nm in Liverpool and GSDs of approximately 1.8 and 1.5 respectively.…”

“…Imhof et al (2005b) measured the road tunnel soot distributions peaking at around 80-100 nm (GSD∼1.85) in the tunnel in Graz. On the other hand, they reported that the soot mode measured in the traffic tunnel in Liverpool was not clearly distinguishable in the distribution and its GMD was around 45 nm (GSD∼2.22).…”

Dispersion of traffic-related exhaust particles near the Berlin urban motorway – estimation of fleet emission factors

“…18% NO x 11.7 0.027 20-25 m Imhof et al (2005) 7-300 80-100 ca. 18% NO x 13.5 0.048 8-20 m Hueglin et al (2006) 7-1000 100 18% NO x 7.9 20 m Imhof et al (2006) 18-700 80 18% tunnel 1.50 (0.08) 0.21 (0.008) n.a. Abu-Allaban et al (2002) 10-400 <90 14% tunnel 0.52-0.54 n.a.…”