The 2021 air quality monitoring data compiled by the EPA shows a downward trend of concentrations across all air pollutants for five consecutive years. The average number of days with Air Quality Index (AQI) of 100 or less, meaning in the categories of Good or Moderate AQI, exceeded 90% in 2020 and 2021. Also, there were fewer and fewer days with AQI above 100 (Unhealthy categories) in both years and zero days with AQI of 200 or higher (Very Unhealthy and Hazardous categories).

The EPA pointed out that the national PM_2.5 concentration reached the goal of an average concentration of 15.7 μg/m³ for the whole of 2021 and the ultimate goal of an average annual concentration of 15 μg/m3 for 2020 to 2023, as set by the Executive Yuan-approved Air Pollution Control Plan. As for ozone, the average annual concentration continues to drop. Compared to recent years, in 2021 there was a significant decrease in hourly values of ozone over 120 ppb as well as a drop in 8-hour periods of ozone over 60 ppb. The number of station-days in 2021 that had an 8-hour ozone red alert showed an improvement of nearly 60% over the previous year. 

The primary cause of poor air quality in 2021 was PM_2.5, mostly present from January to March. Further analysis reveals poor horizontal and vertical dispersions caused by meteorological factors such as stationary air masses and low altitude of the mixing layer. Furthermore, the Central Weather Bureau monitoring data displays an increase in hours with low wind speed and a clear drop of rainfall from January to March 2021. Neither of these meteorological conditions helps disperse particulate matter, leading to increased accumulation of PM_2.5 concentration.

The EPA noted that, since the revision of the Air Pollution Control Act (空氣污染防制法), it has worked on tightening control measures and evaluating 101 sets of relevant regulations as well as completing amelioration of multiple pollution sources ahead of schedule. For example, the number of Phase-1-to-3 large diesel vehicles taken off the road reached double the annual goal, and the goal of phasing out 1.2 million motorcycles has been achieved for Phase-1-to-4 motorcycles from 2020 to 2021.

For stationary sources, state-run enterprises have seen their pollution emissions reduced by 45% compared to 2016. Ninety-eight percent of their boilers listed for control have been improved. Other accomplishments include setting emission standards for hazardous air pollutants (HAPs) and tightening emission standards for the cement industry. 

As for mobile sources, the results so far include the removal of 38% of Phase-1-to-3 high-polluting large diesel vehicles, 26% of old motorcycles, and assistance given to local governments in designating 15 air quality maintenance zones. For regulating fugitive sources, amended regulations strengthened control of the restaurant industry and construction projects. The number of airborne dust incidents in Zhuoshui River and Kaoping River dropped from nine and eight in 2020 to four and zero, respectively, in 2021.

The EPA will continue to work with other central government departments and local governments to safeguard air quality and protect public health by reducing air pollution emissions. 

Excerpt from Major Environmental Policies, February 2022