# A Study on Particulate Matter from an Area with High Traffic Intensity
## 2 Materials and Methods  
The concentration of particulate matter was determined using two different measurement methods with two separate pieces of equipment. Both instruments were calibrated, metrologically certified, and accredited by the RENAR (Accreditation Association of Romania). Two different sets of results were recorded. Over a 23-day episode between 15 July 2022 and 7 August 2022, measurements were taken using gravimetric impactors. Additionally, on 25 September 2022, measurements were taken using both the DLS method and gravimetric impactors in parallel. The first measurement equipment consisted of gravimetric impactors that measure particulate matter concentrations through weight comparisons of charged versus uncharged fiber glass filters. These impactors, produced by Sven Leckel GMBH, Berlin, Germany, under the model's name LVS3 (Low Volume Sampler), are specially designed to aspirate air through constructed nozzles at a rate of 55 Nm\({}^{3}\)/24 h. During a 24 h measurement range, particles of a specific dimension are captured on a glass fiber filter. The charged filter is then weighed and compared to the initial state of the uncharged dry filter, determining the concentration of particulate matter of the targeted dimension. The measurement equipment is in accordance with the European standard CEN EN 12341 [31]. The determination of the concentrations is performed by weighing the charged filters (\(\O\) 40 mm) and subtracting the initial value of the uncharged filter. The result in grams is divided by the air flow measured in 24 h that is aspired through the impactor nozzle and multiplied by 10\({}^{6}\) to reach a result measured in \(\upmu\)g/m\({}^{3}\). The measurements were taken under normal temperature and pressure conditions. This measurement method allows for microscopic analysis of the captured particles because of their deposition on the filters, which is an analysis that is presented in this research paper. The microscopic analysis was performed with the Quanta FEG-250 SEM produced by ELECTI, Zaragoza, Spain, which is an environmental scanning electron microscope used for high-resolution imaging, and the composition analysis used energy-dispersive X-ray microanalysis (EDS). A section of the fiber glass filter was used under microscope to visualize the dust particles at a 10,000 times magnification which shows different sized particles below 10 \(\upmu\)m.  
The second measurement equipment was a spectrometer using light scattering to determine the concentration of particulate matter, allowing for measurements to be taken every second, leading to detailed concentration readings over the timespan of the 24 h measurement period. This equipment is produced by GRIMM Aerosol Technik, part of Durag Group, Hamburg, Germany. Measuring the fluctuations in intensity of the light scattered from a suspension or solution allows for the determination of the particle size. This method is widely known as dynamic light scattering (DLS), although it is also referred to as photon correlation spectroscopy (PCS) and quasi-elastic light scattering (QELS). The latter terms are more frequently encountered in older literature. DLS finds its primary application in the analysis of nanoparticles. It is commonly employed for tasks like determining the size of nanogold, proteins, latex particles, and colloids. Typically, this technique is most effective for submicron particles and can accurately measure particle sizes below a nanometer. Within the range of microns to nanometers, when it comes to size measurement (excluding thermodynamics considerations), the distinction among molecules (e.g., proteins or macromolecules), particles (e.g., nanogold), and even a secondary liquid phase (e.g., emulsion) becomes less clear. While DLS can be utilized as a tool to investigate complex fluids like concentrated solutions, this particular application is relatively less common compared to particle sizing [32].