The EPA's initial analysis of the 2020 air quality monitoring data shows that the annual average concentrations of all pollutants including PM_2.5 had decreased. Ozone concentration went from a slow rise to a slight decrease. The monitoring results indicate that the overall air quality has been improving year after year.

The EPA says that the percentage of days with good air quality index (AQI) has been on the rise in the past five years. The number of days with good and moderate AQI (AQI 100) accounted for over 90% in 2020. The number of red alerts caused by PM_2.5 and detected by monitoring stations throughout the country went from 146 in 2019 to 15 in 2020, displaying a significant air quality improvement.

The EPA points out that the decrease in the number of days with poor air quality (AQI > 100, orange alerts indicating unhealthy for sensitive groups) year after year has led to changes in the significance of major pollutants. PM_2.5 and eight-hour ozone average concentration had both been main indicator pollutants through the years. However, the percentage of eight-hour ozone concentration as the indicator pollutant had surpassed PM_2.5 since 2019 and become the main indicator pollutant for poor air quality. In other words, PM_2.5 and its impact has continued to drop while the change or decrease in ozone concentrations has been less obvious.

The percentage of eight-hour ozone concentration as the main pollutant has been on the rise year after year, but in fact the number of orange alert days has gradually decreased in the past two years. Long-term monitoring also shows lowered peak ozone concentrations. A closer look into the changes in ozone concentrations reveals that concentrations of ozone precursors such as nitrogen oxides (NOx) and volatile organic matters have continued to decrease in the past ten years, hence high-concentration ozone was less likely to form and therefore fewer high-concentration ozone episodes occurred. However, lower NOx concentration slowed down ozone depletion causing ozone concentration to increase, and the transboundary ozone has been on the rise, resulting in higher background ozone concentrations.

To investigate the environmental changes that might be related to the improved air quality, the EPA looked into the monitoring data from the Central Weather Bureau (CWB), which shows that the total rainfall decreased and the total hours of low wind speed increased in 2020. Although this meteorological condition is unfavorable for washing away particulate matter in the air or dispersion, the PM_2.5 concentration was still lower in 2020 compared to 2019, reflecting that air pollution control was effective. The monitoring results from CWB also show improved visibility in 2020 than in 2019, consistent with what would be expected with lower PM_2.5 concentrations.

The EPA has been jointly implementing the Air Pollution Control Action Plan () (2020-2023) with local governments and other central departments to reduce emissions of primary particulate matter, sulfur oxides (SOx), NOx, and volatile organic compounds. The implementation of the Plan was focused on four areas: stationary pollution sources, mobile pollution sources, fugitive pollution sources, and comprehensive management. Under the joint effort, the national average PM_2.5 concentration was 15.0g/m³ between 20 January and 20 December 2020, a significant improvement compared to 17.2g/m³ in the same period in 2019. With such achievement, the EPA is expecting to reach the goal of lowering the annual national average concentration of fine particulate matter to 15g/m³ by 2023, and the objective of increasing the number of days with good air quality by 1% year to year and decreasing the number of days with poor air quality by half earlier than planned.

Excerpt from Major Environmental Policies, Jan 2021