Roadside measurements of fine and ultrafine particles at a major road north of Gothenburg
Introduction
There is an increased concern about human exposure to air particles originating from vehicle traffic. In an urban atmosphere the sources of particles could be divided into two major source categories, one that contributes mostly to the number concentration, while the other is related to the mass loading of particles (Ruuskanen et al., 2001). The traffic is without doubt one of the most dominant source of particles in urban areas. Parallel to this the research related to environmental problems associated with urban aerosols have been focused on respirable particles regarding health problems and on even larger particles regarding soil and deterioration of surfaces on buildings and other objects. The PM10 and PM2.5 concepts, measuring mass of particles with a diameter <10 and 2.5 μm, respectively, have been the dominant way to monitor particles (Harrison et al., 2000). Furthermore, the majority of available epidemiological and exposure studies of airborne particles are related to PM10 or PM2.5 with or without subsequent chemical analysis (McMurry, 2000; Harrison and Yin, 2000).
From numerous studies a link between elevated PM10 particle concentrations and respiratory diseases has been found (e.g. Brunekreef and Dockery, 1995). Lately, there have been a few studies that do not focus on the inhaled mass but rather on the number or the total surface of particles inhaled (e.g. Oberdörster, 2001). One of the reasons for this approach is that the larger particles, carrying the bulk of the mass, are deposited in the upper airways and are more easily removed. Particles smaller than about 2.5 μm, on the other hand, can travel into the lungs and subsequently be deposited in the alveolar region. It has been shown that in the alveolus, the presence of a number of particles is more important to the adverse effect than total mass (e.g., Seaton et al., 1995). Donaldson et al. (1998) suggested that ultrafine particles (particles with an aerodynamic diameter <100 nm) could penetrate into pulmonary interstitial spaces and thus provoke inflammation.
Known urban sources of ultrafine particles, which contribute significantly to the number concentrations, are combustion processes and in particular traffic-related emissions. As traffic density is increasing rapidly in most parts of the world the problems with the emissions of traffic-related pollution is one of the hardest to solve, even if technical development can reduce the emissions from each vehicle substantially. At several urban sites there have been a decline in average mass concentrations while the number concentrations of particles are still increasing (Morawska, 2001). Nowadays, more measurements are available on number distributions and corresponding number concentrations at urban sites (e.g. Ruuskanen et al., 2001; Ruellan and Cachier, 2001; McMurry, 2000). Most of the results from such studies reveal some inconsistency in monitoring PM10 as a substitute for number concentration measurements. Still, one must keep in mind that environmental and health problems linked to aerosols is a field of research where there are many aspects that are not yet known or fully understood. Consequently, many different types of studies are needed in order to be able to describe the role of aerosols.
The aim of this study is to evaluate and quantify the contribution of ultrafine particles from traffic close to a road with respect to the size distribution and major meteorological parameters. The site chosen was located outside the main city thereby limiting other nearby sources. The results are discussed and compared with previous studies focused on particles at urban sites.
Section snippets
Experimental
The measurement site is situated along a main commuting road (RV45) 15 km north of the city of Gothenburg (Sweden), with 600,000 inhabitants (Fig. 1). The road is parallel to the Göta River and runs in north-south direction at the bottom of a 2 km wide valley heading towards Gothenburg. RV45 is a straight four-lane road with a speed limit of 90 kph and there are no industries or other anthropogenic sources in the vicinity. The vehicles are expected to run steadily with constant speed when passing
Results and discussion
All the instruments were running continuously over the campaign. Number concentration data were successfully collected during 430 h out of the total 500 h of the campaign measurements, while the PM2.5 data were successfully collected 18 out of 21 days. The meteorological parameters, relative humidity, temperature, solar radiation and precipitation showed no significant correlation with any of the traffic-related particle variables. The major variables influencing the concentrations of particles
Conclusions and implications
According to the results from this study, PM10 and PM2.5 will not necessarily tell anything about the levels of ultrafine particles. In addition, the limited number of studies performed gives an incomplete picture about the variability of emissions due to, for example, different sites, different vehicles, different speeds and working load of the engines. In this study, most vehicles are assumed to travel at a constant speed of about 90 kph. This is close to an ideal workload for many types of
Acknowledgments
This project was partly funded by a grant from The Gothenburg Region Association of Local Authorities. The Environmental Office in Gothenburg is acknowledged for their contribution with meteorological and TEOM data. Dr. Valentin Foltescu, Petter Svanbom and Anders Ahlberg are greatly acknowledged.
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