The determination of the d50 diameter was done graphically on a log-probability diagram, the diameter of
particles (y-axis logarithmic scale) and percentage of the aggregate mass of particles with a diameter ≤ di (x-axis
scale probability) were calculated.
Figure 7 shows the log-probability graph (100 - cumulative mass in % according to floor diameter). The median
aerodynamic diameter d50 obtained from the right of the graph was 2.6 μm. It means that 50% of the mass of PM-10
particles had a diameter less than 2.6 μm.
From the log-probability diagram of Figure 7, we obtained for the PM-2.5 an average grade of 36.1μg/m3. This
content represents 90% of PM-3. The study of PM-3 is therefore a very good approximation for evaluating the
alveolar fraction (PM-2.5).
As a result, the size distribution of PM-10 showed that fine particles of small size are predominant: the alveolar
fraction (PM-2.5) constituted 48% of PM-10. The fine fraction (PM-1) which was deposited in an irreversible way
in the alveolar pouches constituted more than a third of PM-10 and about two thirds of PM-2.5.
Overall, we found that in this urban site influenced by emissions from traffic, pollution by PM-10 and PM-2.5
was very high. The threshold limits in force in the U.S. (15 μg/m3 annual average and 65 μg/m3 daily mean for PM-
2.5) and EU (25 at 40 μg/m3 for PM-10 and 15 at 25μg/m3 for PM-2.5) [2 and 11] were widely exceeded.