## 1 Introduction  
Emission regulations have significantly reduced the number of floating particles on roads since the 1990s. Although the amounts of sulfur oxides and nitrogen oxides floating in the air have decreased, they have remained at certain concentration levels. According to the World Meteorological Agency, the concentration of suspended solids in Seoul has been relatively high compared to those in major cities worldwide for the last 10 years. In addition to exhaust emissions, particles such as road dust resuspension, road surface abrasion, brakes, and tire wear also contribute to air particle concentrations [1]. As the amount of fine dust emitted by engine combustion has greatly reduced, there has been increasing interest in fine dust generated by non-exhaust sources. In the road pollutant sector, as announced by the German Environment Agency, the relative contribution of non-exhaust emission fine dust will account for 93% of PM10 and 74% of PM2.5 by 2030, and similar results were predicted by the NAEI (National Atmospheric Emissions Inventory) [2]. The most important factors that result in direct particulate matter emissions are tires, brakes, clutches, and road wear [3]. Braking rotors that require the ability to absorb the high temperature and friction energy generated by vehicle braking and that can quickly release heat energy have been inspected for decades. Gray cast iron has been widely selected because of its poor wear properties in contact with brake pads and the low generation of harmful substances owing to wear processes [4]. However, there have been continuous developments and changes in the materials of brake pads. Brake pads are typically made of asbestos, semi-metallic(SM) materials, non-asbestos organics (NAO), and low-strength and low-carbon materials [5; 6]. Asbestos fibers are largely avoided because of their carcinogenic properties, and new asbestos-free friction materials and brake pads have been developed [7]. Automotive brake pads typically include reinforcing fibers, binders, abrasives, lubricants, and fillers. Reinforced fibers such as brass, copper, steel, aramid, carbon, and glass are used to determine the main components of brake pads. A binder holding the ingredients of a brake pad provides bonding strength, and phenolic resin is generally used [8]. Studies have found that reinforced fibers and abrasive components are used for significant changes in the friction coefficients and strength. The friction coefficient depends on the features of the contact surfaces and the operating conditions, such as contact pressure, sliding velocity, and temperature. The formulation of brake pad components mainly affects the wear rate of the brake pad system [5; 8; 9; 10; 11]. Therefore, the ingredients of the pads used in the friction experiment vary from study to study [12]. Although the components of brake materials may vary according to the manufacturer, the main composition of particulate matter emitted by brake applications shows common components: iron, copper, antimony, and barium [1; 13]. Several challenges arise when studying non-exhaust traffic-related sources and particulates resulting from brake wear. One reason is that there is a lack of an experimental method for releasing and collecting fine particles from brake pads. Euro published the official method of sampling and measuring brake particle emissions from full-friction brakes in a dynamometer system in November 2022, but it still needs a standard form in other methods. This leads to different approaches of our study for comparing results. To analyze the fine dust generated from brake pads, it is necessary to collect fine particles generated from an actual vehicle. However, when measuring brake particles in the air during field tests, it may be difficult to distinguish them from particles produced from other sources, such as construction, tires, and road resuspended dust [14; 15]. Brake dynamometer experiments have implemented brake discs, pads, hydraulic systems, and vehicle power sources.