What question did this study set out to answer?

This study aims to analyze PM2.5's chemical characteristics and assess multi-pollutant health risks during different pandemic stages.

February 25, 2026Open Access

Integrated analysis of PM2.5 chemical characteristics and multi-pollutant health risks in Central Taiwan: Implications for optimizing the air quality health index (AQHI) during the COVID-19 pandemic

Key Points

This study aims to analyze PM2.5's chemical characteristics and assess multi-pollutant health risks during different pandemic stages.
Analyzed PM2.5 chemical characteristics from 2020 to 2022 in Taichung, Taiwan
Examined concentrations of PM2.5, O3, and NO2 across industrial and traffic sites
Conducted health-risk analysis using AQHI and outpatient records stratified by pre-, during-, and post-pandemic stages
Performed source apportionment analyses for PM2.5 pollutants
PM2.5 characteristics changed significantly due to COVID-19 restrictions
Total water-soluble ions increased due to higher electricity demand during the pandemic
PAH concentrations decreased during lockdown but rebounded sharply post-pandemic
High-risk AQHI levels were linked to increased respiratory and cardiovascular morbidity
AQHI proved to be a more sensitive metric for assessing short-term health risks than AQI

Abstract

Conventional Air Quality Index (AQI) systems often underrepresent multi-pollutant health impacts. The Air Quality Health Index (AQHI), which integrates daily concentrations of PM 2.5 , O 3 , and NO 2 to estimate population-level health risks, addresses this limitation by accounting for multi-pollutant exposure effects. This study investigated the chemical characteristics of PM 2.5 in Taichung, Taiwan, from 2020 to 2022, focusing on polycyclic aromatic hydrocarbons (PAHs) and water-soluble ions (WSIs) across industrial and traffic areas. During pandemic restrictions, remote work and online learning increased electricity demand, coinciding with elevated total water-soluble ion concentrations, largely driven by increases in non–sea-salt sulfate (nss-SO₄ 2− ; 11.8 ± 4.12 μg/m 3 ) in the industrial area. In contrast, PAH concentrations declined during lockdowns but exhibited a pronounced rebound during the warm season in the post-pandemic period, reaching approximately two to three times the levels observed during the pandemic stage. Source apportionment analyses indicated that traffic-related emissions, particularly diesel exhaust, were the dominant contributors to ambient PAHs. Health-risk analysis based on AQHI and outpatient records (2016–2022; stratified by pre-, during-, and post-pandemic stages) revealed that high-risk AQHI levels (≥7) were associated with increased respiratory and cardiovascular morbidity. Lag-effect analysis showed acute and persistent risks from PM 2.5 and NO₂, whereas O₃ exhibited delayed inverse statistical associations. The findings demonstrate that AQHI is a more sensitive short-term, health-relevant metric than AQI under pandemic-altered activity patterns. This integrated approach offers empirical evidence supporting Taiwan's adoption of AQHI for risk communication and for protecting vulnerable populations. • COVID-19 restrictions reshaped PM 2.5 composition across industrial and traffic sites. • Increased power demand elevated nss-SO₄ 2− , while PAHs rebounded sharply post-pandemic. • High-toxicity HMW-PAHs were dominated by diesel and combustion-related emissions. • AQHI revealed stage-specific cardiovascular and respiratory risks with clear lag effects. • AQHI outperformed AQI in capturing short-term multi-pollutant health risks.

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Cite This Study

Chen et al. (Mon,) studied this question.

synapsesocial.com/papers/699e90eff5123be5ed04e2a7 https://doi.org/https://doi.org/10.1016/j.scitotenv.2026.181584

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