Physico-chemical Characteristics and Evolution of NR-PM1 in the Suburban Environment of Seoul

Abstract

In South Korea, particulate matter (PM) is generated from various emission sources, including domestic air pollutants and long-range transport. Effective air quality policies require an understanding of the chemical characteristics of PM and differences between urban and non-urban areas (suburban and background areas). We analyzed the chemical characteristics of non-refractory submicron aerosols (NR-PM₁) in Yongin City, a suburban area southeast of Seoul, using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) in spring/summer. In spring/summer, photochemical reactions resulted in the highest proportion of Organic Aerosol (OA) among NR-PM₁. Positive matrix factorization (PMF) revealed four OA sources: Primary OA and Secondary OA (Oxidized Primary OA (OPOA), Less Oxidized Oxygenated OA (LO-OOA), and More Oxidized Oxygenated OA (MO-OOA)). OPOA was formed from the oxidation of emissions from biomass burning and coal combustion; LO-OOA and MO-OOA were correlated with inorganic compounds and influenced by long-range transport. The majority of OA was SOA (82%). High temperatures and humidity accelerated the conversion of SO₂ to SO₄²⁻, resulting in the proportion of SO₄²⁻, second only to OA. Despite favorable conditions for nitrate formation in ammonium-rich conditions, the proportion of NO₃⁻ was relatively low due to the decomposition of NH₄NO₃ into gaseous NH₃ and HNO₃ at high temperatures. This indicated that while ammonium-rich conditions are conducive to NH₄NO₃ production, elevated temperatures lead to its decomposition, resulting in lower NO₃⁻ concentrations in spring/summer. In the case study, for the case associated with long-range transport, the PM concentration increased due to inorganic compounds such as NO₃⁻ and SO₄²⁻. Conversely, in cases of domestic air stagnation, the concentration of PM increased primarily due to the presence of OA. These findings provide crucial insights for air quality management in suburban areas and can guide policies to reduce PM levels in spring and summer.