Ten Years Behavior of Carbonaceous Ultrafine Particulate Matter (PM_0.1) in Phnom Penh, Cambodia

Abstract The long-term behavior of mass concentration of ambient ultrafine particulate matter was discussed on samples collected at a site located in Phnom Penh City, Cambodia, between 2011-2020. A cascade air sampler that can collect PM 0.1 (<0.1 μm) has been used at a site located on a roof floor of a 5-story building on the campus of the Institute of Technology of Cambodia (ITC) located near the central part of Phnom Penh City. The main goal was to investigate PM 0.1 and carbon compositions, including elemental carbon (EC) and organic carbon (OC). As a result, PM 0.1 increased by about 2.3 times, and PM 0.1 remarkably increased in the past ten years. EC and soot-EC, which are considered to be road traffic sources, also increase PM0.1 mass concentration. Soot-EC and the number of vehicles per year are correlated. Biomass burning indicators such as OC, char-EC, and hot spots number increase at the same time. Consequently, it is considered that the dry season (January to March) is greatly affected by open fires in Cambodia and neighboring countries.