研究臺中市超細懸浮微粒之特性、來源與歸趨

Abstract

超細懸浮微粒（Ultrafine particles, UFPs，粒徑 <0.1 µm）具有高度健康風險，但由於大氣過程複雜，其精確模擬與控制仍具挑戰性。本研究針對亞熱帶都市環境的臺中市進行超細懸浮微粒動態特徵之探討。 研究利用 2021 年 4 月的觀測資料，包含粒徑數目分布（PNSDs, 11.8–593.5 nm）、硫酸濃度以及氣象參數，並採用配置 15 個粒徑分箱的 GEOS-Chem-TOMAS 模式，測試五種成核機制（Base、Binary、Binary ion、Ternary、Ternary ion），以評估主要新粒子生成（New Particle Formation, NPF）過程。 模擬結果顯示，Base、Ternary 與 Ternary ion 機制產生零星成核爆發，而 Binary 機制作用極為有限。雖然硫酸（H2SO4）濃度高峰與爆發現象同時出現，但線性相關性極弱（Pearson R ≈ -0.04），顯示 NPF 為高度複合性的多因子過程。 統計比較結果指出，GEOS-Chem-TOMAS 模式對各粒徑模式下的粒子數濃度（PNCs）皆有顯著低估（NMBs：-8.5% 至 -90.9%），相關係數亦偏低（0.06–0.21），顯示模式難以重現觀測變化。 重要的是，無論觀測或模擬皆顯示在 2021 年 4 月缺乏典型「香蕉型」NPF 事件，而背景氣膠主要由 Aitken 與累積模態主導。模擬中的零星爆發未導致持續成長，顯示臺中市大氣條件普遍不利於持續 NPF 發生。 本研究結果凸顯模式改良之迫切需求。未來建議改進成核與成長參數化、引入更高解析度之都市排放清單，並提升氣象輸入準確性。同時，後續觀測應增設 <10 nm 粒徑偵測儀器，以加強對 NPF 的限制與模式評估。

Ultrafine particles (UFPs, <0.1 µm) pose significant health risks, yet their accurate modeling and control remain challenging due to complex atmospheric processes. This study investigated UFP dynamics in Taichung City, Taiwan, a subtropical urban environment. The research utilized comprehensive observational data from April 2021, including particle number size distributions (PNSDs, 11.8–593.5 nm), sulfuric acid, and meteorological parameters. The GEOS-Chem-TOMAS model, configured with 15 size bins, tested five nucleation schemes (Base, Binary, Binary ion, Ternary, Ternary ion) to assess dominant New Particle Formation (NPF) mechanisms. Simulation results showed sporadic nucleation bursts from Base, Ternary, and Ternary ion schemes, with negligible activity from Binary schemes. While elevated sulfuric acid (H2SO4) peaks coincided with bursts, a weak linear correlation (Pearson R ≈ -0.04) indicated NPF is a complex, multi-factorial process. A statistical comparison revealed the GEOS-Chem-TOMAS model consistently and significantly underestimated observed particle number concentrations (PNCs) across all modes (NMBs: -8.5% to -90.9%). Correlation coefficients were low (0.06–0.21), showing the model struggled to reproduce observed variability. Crucially, both observations and simulations consistently lacked classical "banana-shaped" NPF events throughout April 2021. Instead, background aerosols in Aitken and accumulation modes dominated. Sporadic simulated bursts did not lead to sustained growth, suggesting Taichung's atmospheric conditions were generally unfavorable for sustained NPF. These findings highlight the critical need for targeted model improvements. Future enhancements should focus on refining nucleation/growth parameterizations, incorporating higher-resolution urban emission inventories, and enhancing meteorological inputs. Employing sub-10 nm detection instruments in future observations would also improve NPF constraint and model evaluation.