Unveiling secondary inorganic PM2.5 pollution in northern Taiwan: The role of aerosol acidity and transformation processes
Journal
Science of The Total Environment
Journal Volume
969
Start Page
178979
ISSN
0048-9697
Date Issued
2025-03-15
Author(s)
Ankita Katoch
Chi-Chi Lin
Thi Phuong Thao Ho
Kuan-Ting Liu
Atar Singh Pipal
YU-HSIANG CHENG
Abstract
Efforts are being made to manage air pollution in Taiwan. To address the concern of anthropogenic aerosol loadings, it is imperative to comprehensively monitor and analyze the physicochemical and thermodynamic properties of secondary inorganic PM2.5 constituents. This study focuses on the high-resolution inorganic aerosol chemistry in an urban area of northern Taiwan, using hourly measurements of trace gases and water-soluble inorganic ions (WSIIs), integrated with the ISORROPIA II thermodynamic model. Our findings indicate that aerosol acidity (pH) and aerosol liquid water content (ALWC) are crucial in controlling gas-to-particle phase partitioning of fine aerosols and PM2.5 mass loadings in the ambient air. The relationship between ALWC and the conversion ratios, including sulfur oxidation ratio (SOR), nitrogen oxidation ratio (NOR), and ammonia conversion ratio (NHR), indicates that secondary ion formation increases with higher ALWC, thereby directly affecting air quality. The diurnal pattern of NOR highlights the significant role of photochemical reactions in NO3− formation during the day, while the nighttime increase in SOR levels, coupled with their daytime decrease, supports the occurrence of nighttime aqueous-phase oxidation driven by elevated ALWC. Peak neutralization of secondary anions by NH4+ was observed during winter under NH3-rich conditions, leading to a hygroscopic increase in PM2.5 mass concentrations. The pH sensitivity analysis of regional atmospheric secondary PM2.5 formation identified NO3− as the limiting factor. This suggests that reducing HNO3 and precursor NOx levels, rather than NH3, would more effectively and quickly lower PM2.5 concentrations. Implementing such a strategy could offer a cost-effective and impactful solution for managing high aerosol loadings in northern Taiwan.
Subjects
Inorganic nitrogen
Oxidation ratios
Secondary transformation
Thermodynamic modeling
SDGs
Publisher
Elsevier BV
Type
journal article