2.1. Case study sampling site
In order to study the magnitude of air pollution by different size distributions of aerosol particles, we selected a
site in the city of Algiers in Algeria as presented in the European classification that is directly influenced by
emissions from road traffic [9]. Such site allows access to maximum levels of pollution that an urban population can
be exposed. The selected site where measures were carried out was located at the National Polytechnic School, 10
km in the east of Algiers. The sampling station was located at an altitude of 4m and 9m from the edge of the NR n°5
(National Road). In 2000, the major highway had a volume of 25,000 vehicles per day with approximately 15% of
them buses and heavy diesel vehicles [10]. The case study site was characterized by the absence of obstacles and
good natural ventilation. In addition, there were no industries nearby which could emitting particles and thus
interfere with assessment of the effect of air pollution due to road traffic.
2.2. Sampling mode
For the measurements by size distribution, a high volume sampler, the HVS-PM-10 equipped of cascade
impactor (brand Andersen) with four levels was used. The device shown in Figure 1 was composed of three main
parts:
• The High Volume Sampler (HVS) which represents the body of this sampler consists mainly of:
- An air aspiration turbine ;
- Levels of selection that are use as filters racks in order to sort the particles by size;
- An electronic flow controller, MFC (Mass Flow Controller), which maintains a constant flow of air aspiration. In
case of clogging of the media filter, the MFC acts on the engine power by the electronics regulation of the voltage.
• Thes electively top of PM-10 which i s t he a rea o f 10 μm fragmentation by direct impact. This direct impact is
based on the aerodynamic effect induced by the presence of 9 circular nozzles positioned above a smooth impaction
surface. Particles below the cutoff of 10μm are driven by the air flow through the nozzles and collected on the filter.
While larger particles deviate from the flow and impacting on the flat surface of impaction due to their higher
inertia. In order to avoid re-entrainment of coarse particles, the impact surface is greased by silicone oil and cleaned
regularly.
• The Anderson cascade impactors allows for a measure of particles by size distribution; it has four levels and offers
access to the 5 size classes: 10 to 7 μm, 7 to 3 μm, 3 to 1.5 μm, 1.5 to 1 μm and below 1 μm (Figure 2).
The flow rate was set at 1m3/min. The sampling time was 24 hours.
2.3. Processing and analysis of samples
The particles were collected on membranes filters, fiberglass Whatman 20 x 25 cm for the final filter and 10 x
12cm for filters of the levels of cascade. In order to determine the content of PM-i, the size of each floor filters are
weighed before and after collect at a precision of 0.1 mg.
The atmospheric concentration of PM-i was expressed in μg/m3.