Particle size distribution and particle mass measurements at urban,near-city and rural level in the Copenhagen area and Southern Sweden

Abstract

Abstract. Particle size distribution (size-range 3-900 nm) and PM10 was measured simultaneously at an urban background station in Copenhagen, a near-city background and a rural location during a period in September-November 2002. The study investigates the contribution from urban versus regional sources of particle number and mass concentration.The total particle number (ToN) and NO x are well correlated at the urban and near-city level and show a distinct diurnal variation, indicating the common traffic source. The average ToN at the three stations differs by a factor of 3. The observed concentrations are 2500 # cm −3 , 4500 # cm −3 and 7700 # cm −3 at rural, near-city and urban level, respectively. PM10 and total particle volume (ToV) are well correlated between the three different stations and show similar concentration levels, in average within 30% relative difference, indicating a common source from long-range transport that dominates the concentrations at all locations.Measures to reduce the local urban emissions of NO x and ToN are likely to affect both the street level and urban background concentrations, while for PM10 and ToV only measurable effects at the street level are probable. Taking into account the supposed stronger health effects of ultrafine particles reduction measures should address particle number emissions.The traffic source contributes strongest in the 10-200 nm particle size range. The maximum of the size distribution shifts from about 20-30 nm at kerbside to 50-60 nm at rural level. Particle formation events were observed in the 3-20 nm size range at rural location in the afternoon hours, mainly under conditions with low concentrations of preexisting aerosol particles.The maximum in the size distribution of the "traffic contribution" seems to be shifted to about 28 nm in the urban Correspondence to: M. Ketzel (mke@dmu.dk) location compared to 22 nm at kerbside. Assuming NO x as an inert tracer on urban scale allows to estimate that ToN at urban level is reduced by 15-30% compared to kerbside. Particle removal processes, e.g. deposition and coagulation, which are most efficient for smallest particle sizes (<20 nm) and condensational growth are likely mechanisms for the loss of particle number and the shift in particle size.

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

“…Figure 6 shows that both distributions were dominated by small, probably nucleation originated particles with a peak size of approximately 20 nm. Similar observation was also reported by Wehner and Wiedensohler (2003) and Ketzel et al (2004). Multimodal lognormal distribution was fitted to the measured distributions to enable the particle density calculation procedure described above.…”

“…These values are in good agreement with our study. Ketzel et al (2004) found that the traffic related distributions peaked at 22 nm in the centre of Copenhagen. In addition, Wehner and Wiedensohler (2003) reported the peak in the urban number size distribution around 20 nm.…”

“…According to Imhof et al (2005a); Janhäll et al (2004); Ketzel et al (2004) and Wåhlin et al (2001) the size distributions measured at the roadside were dominated by nucleation mode particles with a relatively constant peak size of 20 nm. In laboratory and chase measurements the nucleation mode existence and peak diameter show great variation (Kittelson et al, 2004;Vaaraslahti et al, 2004;Rönkkö et al, 2006).…”

Transport impacts on atmosphere and climate: Land transport

“…The total particle number measured in urban areas often correlates well with NO x and shows a distinct diurnal variation, indicating a common traffic source (Ketzel et al, 2004;Hussein et al, 2004). Traffic emissions are able to affect submicron particle number concentrations around major roads and may be a dominant source of ultrafine particles (PM 0.1 ) in the urban atmosphere (Despiau and Croci, 2007;Rodriguez et al, 2007).…”

“…Size resolved measurement data reveal that about 90% of these particles have an aerodynamic diameter below 0.5 mm (e.g. Birmili et al, 2009;Ketzel et al, 2004Ketzel et al, , 2007Samaras et al, 2005) and hence are in the health relevant size segment. Vehicle emissions of air pollutants strongly depend on the exhaust emission control devices and their operation efficiency in a given year.…”