臺灣空氣品質的氣候特徵與大氣環流之影響

The monitoring of air quality in Taiwan has laid the groundwork for a substantial database in recent years. Besides tracking various air pollutants' concentrations, the adoption of two indices, the Pollution Standards Index (PSI) previously used and the current Air Quality Index (AQI), has standardized the assessment of air quality. While previous studies predominantly focused on individual pollution events or regional air quality, fewer analyses were approached from a climatic perspective. Hence, this study separately tallies the proportions of exceeded PSI and AQI pollution monitoring instances, analyzes the primary pollutants contributing to these exceedances, and presents Taiwan's air quality changes over time through yearly cycles and interannual variations. This year's research outcomes on Taiwan's air quality have materialized in two published papers. One paper authored by Hung and Shih (2023) scrutinizes Taiwan's air quality changes over recent decades, including the COVID-19 period. Their findings underscore Taiwan's significant achievements in reducing various common air pollutants such as CO, NOx, PM10, PM2.5, and SO2. However, reducing ozone (O3) has proven considerably challenging due to the intricate interplay of precursor reduction and meteorological influences, contrasting with these achievements. Additionally, another paper, pending publication and approved for review, authored by Hung et al. (2024), compares the daily data of PM10, PM2.5, and O3 concentrations in seven different air quality regions across Taiwan with daily precipitation and NOx concentrations. The results reveal that from mid-autumn to mid-spring, local emissions tend to accumulate due to poor atmospheric dispersion caused by unfavorable environmental wind patterns, compounded by external pollutants brought in by the northeasterly monsoon, resulting in significantly elevated PM10 or PM2.5 concentrations. Precipitation acts as a mitigating factor, reducing particle pollutants not only during the rainy and summer seasons but also during winter and spring, notably affecting the rainier northern region on the windward side of the northeasterly monsoon, lowering PM10 and PM2.5 concentrations compared to the sheltered central and southern regions. Moreover, this study elucidates that the relationship between NOx and O3 concentrations isn't purely linear. Besides the equilibrium among various precursors, factors like sunlight play a crucial role in influencing O3 concentrations.