Seasonal observations of particulate composition are needed to characterize rural air quality near livestock facilities without assuming that nearby emissions determine ambient aerosol chemistry. This study examined PM_2.5 and eight water-soluble inorganic ions in weekly 24 h filter samples collected in Duseo-myeon, Ulsan, South Korea, from June 2023 to November 2025. Seasonal concentrations and nitrate mass fractions were evaluated alongside particulate ammonium-to-sulfate ratios and a stoichiometric neutralization index. PM_2.5 was highest in spring, whereas nitrate was highest in winter and lowest in summer, with seasonal means of 3.00 and 0.26 µg m⁻³, respectively. Spring and winter both frequently exhibited elevated ammonium-to-sulfate ratios, but nitrate exceeded sulfate by mass much more often in winter. The ratio intervals summarize observed composition and do not define thermodynamic thresholds or precursor-sensitivity regimes. The study provides a multi-year composition baseline for this rural site and shows that the seasonal PM_2.5 maximum and the strongest nitrate contribution did not coincide. Weekly sampling, incomplete gas-particle time matching, and the absence of concurrent thermodynamic constraints limit attribution of the observed nitrate abundance to specific sources or formation processes.

The composition of air pollutants in industrial complexes differs from that of general urban areas, often containing more hazardous substances that pose significant health risks to both workers and residents nearby. In this study, PM_2.5 and its 29 chemical components (eight ions, two carbon species, and 19 trace elements) were measured and analyzed at five monitoring sites adjacent to the Yeosu and Gwangyang industrial complexes from August 2020 to December 2024. Chemical characterization and source identification were conducted. The average PM_2.5 concentration was 18.63 ± 9.71 μg/m³, with notably higher levels observed during winter and spring. A low correlation (R = 0.56) between elemental carbon (EC) and organic carbon (OC) suggests a dominance of secondary aerosols. The charge balance analysis of [NH₄⁺] with [SO₄²⁻], [NO₃⁻], and [Cl⁻] showed slopes below the 1:1 line, indicating that NH₄⁺ is capable of neutralizing these anions. Positive matrix factorization (PMF) identified eight contributing sources—biomass burning (10.4%), sea salt (11.8%), suspended particles (7.1%), industrial sources (4.6%), Asian dust (5.2%), steel industry (21.8%), secondary nitrate (16.4%), and secondary sulfate (22.7%). These findings provide valuable insights for the development of targeted mitigation strategies and the establishment of effective emission control policies in industrial regions.