## 1 Introduction
These can be made similar to the actual vehicle environment, but the collected resultants of fine particles are quite different from the real field, and the main reason is the difference in the sampling system. The generated fine particles changed rapidly with some distance between the vehicle and the sampling spot by coagulation and molecularization [16; 17]. Pin-on-disc distribution meters have been frequently used in many studies to identify the friction and wear behaviors of disc brake materials in controlled environments, but each experiment has different results by researchers due to different test methods [18; 19; 20]. In this study, the pin-on-disk method was adopted to find out the friction characteristics in low-temperature areas that are not feasible in actual vehicles and dynamometers. Previous studies controlled the cleanliness of the air surrounding the pin-on-disc, which makes it possible to measure the air abrasion particles generated by the contact pair [14; 21]. The change in the amount of wear of metal materials according to atmospheric components is a well-known fact. As a result, fine particles in the normal state and the experimental state were observed in real time and were tested analyzing the difference of each one. When analyzing brake pad particulate matter, the particle number concentration is an important factor because several studies have found significant values among the distributions. [PERSON] found peaks in a relatively large one micrometer-sized fine particle section during a sampling of light-duty vehicle brake wear [22]. [PERSON] found number concentration peaks around 1 to 6 \(\upmu\)m with different types of pads at different temperatures [23]. There are also results with peaks in sections of tens to hundreds of nanometers in size. Studies on brake dynamometer tests have found several nanoparticles of 100-200 nm analyzed by SMPS around 300 \({}^{\circ}\)C [24]. [PERSON] found the characteristic particle number concentrations of airborne brake wear particles with different brake pads, resulting in peaks at 100, 280, 350, and 550 nm [14; 25]. Studies of brake pad specimens have shown a section where the incidence rate of ultrafine particles increased at 160 \({}^{\circ}\)C [26]. In the low temperature region, an inspection of the first reaction of a brake pad revealed that it corresponded to the evaporation of substances inside the pads, which led to the occurrence of fine particles [27]. In this study, considering the increasing contribution to air pollution from the friction of brake pads, a tribo-meter was used to conduct a friction experiment. In order to simulate the friction shape between the brake pad and the rotor, the surface contact method was selected. In the case of actual brake pads, the temperature rises sharply even if friction proceeds for a few seconds due to heat. Therefore, a pin-on-disc specimen test was designed to minimize the variables caused by temperature. By using a friction tester to analyze the concentration and distribution of particles produced under different driving conditions, the study provides valuable insights into the impact of vehicle deceleration on roadside air pollution. Number concentration data were obtained by analyzing fine particles generated from the friction test. We investigated and analyzed the characteristics of fine particles that depend on the conditions of the experiments.