# Metal Element Traces Sampled from Peri-Urban Road Verge Particulate Matter
## 3 Results and Discussion
### Determination of PM Concentrations Using DLS Spectrometer  
Measurements were taken in the same way to compare the road verge with the garden. The duration of each measurement was approximately 2 h. Each measurement was taken at an interval of 6 sec, determining the concentration levels for PM1, PM2.5, and PM10.  
The sizes of PM pose a threat to human health, being able to pass through the several safety mechanisms in the human respiratory system. PM10 particles are inhalable-sized and able to pass through the nose hair; PM2.5 particles are thoracic-sized, passing through the throat mucus and the lungs; and PM1 particles are alveolar-sized, with the ability to reach and pass the alveoli into the blood stream.  
Temperatures recorded on 29 July 2023 during that measurement episode were at a maximum of 37 \({}^{\circ}\)C and an average of 28 \({}^{\circ}\)C. Wind speed was at an average of 10 km/h, with a wind direction predominantly from E to W and S to N, blowing toward the nozzle of the spectrometer [33].  
Road verge measurements have determined different concentrations of PM, as shown in Table 1.  
The logarithmic dispersion of PM concentrations on the entire measurement episode from the road verge is shown in Figure 6.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Variable** & **PM1 (\(\mathbf{\mu}\)g/m3)** & **PM2-5 (\(\mathbf{\mu}\)g/m3)** & **PM10 (\(\mathbf{\mu}\)g/m3)** \\ \hline Minimum & 5.4 & 6.1 & 6.1 \\ Maximum & 68.6 & 143 & 889.8 \\ Mean & 7.9 & 10.7 & 27.1 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Values of PM1, PM2-5, and PM10 concentrations measured using the DLS spectrometer taken from the road verge.  
Figure 5: Metals present in the analyzed dust samples from the garden area.  
The garden section concentrations of PM are shown in Table 2.  
The logarithmic dispersion of PM concentrations on the entire measurement episode from the garden area is shown in Figure 7.  
Looking at the maximum concentration levels detected, it is evident that along the road verge, concentrations of PM are considerably higher than in the garden area with dense vegetation. The biggest difference could be recognized in PM10, which shows values of 889.8 ug/m\({}^{3}\) for the road verge versus 52.3 ug/m\({}^{3}\) for the garden area.  
Based on these differences, it can be deduced that a dense vegetation area is helpful in blocking quite a high amount of PM concentrations.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Variable** & **PM1 (ug/m\({}^{3}\))** & **PM2-5 (ug/m\({}^{3}\))** & **PM10 (ug/m\({}^{3}\))** \\ \hline Minimum & 7.8 & 8.1 & 8.4 \\ Maximum & 16.4 & 27.7 & 52.3 \\ Mean & 11.7 & 13.3 & 20.1 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Values of PM\({}_{1}\), PM\({}_{2\cdot 5}\), and PM\({}_{10}\) concentrations measured using the DLS spectrometer taken from the garden area.  
Figure 6: Logarithmic dispersion of PM concentrations taken from the road verge.  
Figure 7: Logarithmic dispersion of PM concentrations taken from the garden area.  
In accordance with Romanian legislation, the permissible threshold for PM10 concentration is established at 40 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\) annually, accompanied by a daily threshold of 50 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\). This daily limit must not be surpassed for a duration exceeding 35 days in any given year [34]. On the other hand, concerning PM2.5, the regulations outlined in European Union Directive 2008/50/EC dictate an annual average of 20 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\)[35], a standard to which Romanian Law does not presently provide corresponding limitations. It is worth noting that neither Romanian Law nor the directives within the European Union framework impose any specific restrictions on PM1.