Evaluation of the Chemical Characteristics and Predictive Model of Water-Soluble Inorganic Ions for Fine Particulate Matter Generated in Pohang

Objectives:This study aims to contribute to establishing the regional effective management of fine particulate matter by evaluating the chemical characteristics and contribution of fine particulate matter, and the accuracy of predictive model of fine particulate matter through the measurement of water-soluble inorganic ions (WSIIs) and electrical conductivity for fine particulate matter generated in Pohang.Methods:PM₁₀ and PM_2.5 samples were simultaneously collected using a low volume air sampler from April to November 2022. For sample analysis, cations of Ca²⁺, Mg²⁺, K⁺, NH₄⁺, Na⁺ and anions of Cl^-, NO₃^-, SO₄^2-, and electrical conductivity were measured after pretreatment by ultrasonic extraction. Results and Discussion:The average concentrations of WSIIs for PM₁₀ and PM_2.5 in Pohang were 12.1μg/m³ and 8.5μg/m³, respectively, accounting for 35.5% and 50.0% of each fine particulate matter. The sum of NH₄⁺, NO₃^-, SO₄^2- concentration was found to account for the majority of 71% and 78% of WSIIs in PM₁₀ and PM_2.5, respectively. The PM_2.5/PM₁₀ ratios for NH₄⁺, K⁺, and SO₄^2- were 95%, 89%, and 81%, respectively, mostly present in PM_2.5. The average ratio of PM_2.5/PM₁₀ for NO₃^- was 54%, but it rose sharply to 79% in November when the temperature was low, indicating an increase in contribution to the generation of PM_2.5 in winter. During the sampling period excluding April and July, the ion balance for cations and anions was relatively good at a 1:1 ratio and showed chemical properties of fine particulate matter close to neutral. A regression model was evaluated for the measured electrical conductivity of WSIIs and the concentration of fine particulate matter. The MAE and RMSE values for PM_2.5 were 1.8μg/m³ and 2.4μg/m³, respectively, which were lower than PM₁₀ (MAE 7.5 μg/m³, RMSE 10.3μg/m³), indicating high precision and accuracy. Conclusion:This study confirmed the origin of fine particulate matter generated in Pohang through WSIIs analysis, and suggested that the measured electrical conductivity of WSIIs could be used as a key parameter for measuring the concentration of fine particulate matter.