Starting from the morning of 15 October, overseas ozone (O₃) and fine particulate matter (PM_2.5) gradually started affecting the air quality in Northern Taiwan. At 6 a.m., the O₃ concentration at the Cape Fuguei monitoring station was 80 ppb, and PM_2.5 was 24 mg/m³. In the afternoon, the effect gradually spread to Central and Southern Taiwan. According to the monitoring data gathered at 2 p.m., Western Taiwan had O₃ levels ranging from 70 to 85 ppb, and PM_2.5 levels were around 25 to 35 mg/m³. On the 16th and 17th, the impact of foreign pollutants continued, and the air quality was mostly at the orange alert level. In Southern Taiwan where the wind speed was weaker, there were brief periods of red-level alerts. Starting on the 18th, the northeast monsoon weakened, and on the 19th, it shifted to easterly winds, reducing the influence from abroad. Air quality in Northern Taiwan and the Hsinchu-Miaoli area improved to a moderate level, while Central and Southern Taiwan remained at moderate to orange alert levels. It was estimated that from the 20th onwards, air quality gradually improved to a good to moderate level.

The MOENV had previously advised local governments to monitor changes in air quality and take appropriate actions, including strengthening emission reductions at large factories, controlling dust at construction sites and storage yards, and conducting inspections in the food industry and for open burning activities. The MOENV also coordinated with Taipower's Taichung and Hsinta thermal power plants to reduce air pollutant emissions in advance. Additionally, on 16 October, the MOENV convened its first contingency meeting in this year's air pollution season in Kaohsiung, which was attended by environmental bureau officials from counties and cities south of Yunlin County. They were reminded to collectively reduce emissions from local pollution sources so as to reduce the pollution burden in downwind areas.

The MOENV advised the public to be vigilant. Sensitive groups, the elderly and children, who have weaker immunity should avoid engaging in vigorous outdoor activities for extended periods, and people should use public transportation as much as possible to reduce pollution emissions. Air quality is greatly influenced by meteorological conditions, and short-term weather remains unpredictable. The public is advised to stay updated on the latest air quality information. The latest air quality changes can be found at the Taiwan Air Quality Monitoring Network website (https://airtw.moenv.gov.tw) Different alert levels can be set through the Environmental Info Push App to enhance personal protection and stay informed about air quality information at all times.

Excerpt from Major Environmental Policies, October 2023