Taiwan said it met its annual target for fine particulate pollution in 2025, but officials warned that worsening ozone pollution linked to climate change poses a growing challenge, prompting plans to tighten controls on products that emit volatile organic compounds (VOCs).
The environment ministry said the island’s average PM2.5 concentration in 2025 was 12.6 micrograms per cubic metre, below its target of 14 micrograms, signalling steady progress in reducing fine particle pollution.
PM2.5 refers to airborne particles with a diameter of 2.5 micrometres or smaller that can penetrate deep into the lungs and bloodstream.
The World Health Organization (WHO)’s guideline for annual PM2.5 exposure is 5 micrograms per cubic metre, above which health risks rise steadily. Long-term exposure above about 10 micrograms is linked to higher rates of heart disease, stroke and lung cancer, while levels above 25 micrograms are associated with sharply increased hospitalisations and premature deaths.
Under the government’s air quality policy white paper released in May, Taiwan aims to cut PM2.5 levels to 10 micrograms by 2030 and below 8 micrograms by 2035.
“Ozone is actually the more significant challenge now,” Huang Wei-ming, head of the ministry’s air quality division, told a news conference on Wednesday.
The number of days triggering red alerts for eight-hour ozone exposure totalled 88 this year, down 72 per cent from 2019, but has remained broadly flat over the past five years.
Ground-level ozone is a harmful air pollutant that irritates the respiratory system and is distinct from the protective ozone layer in the upper atmosphere. Average hourly ozone concentrations edged up slightly in 2025, indicating that improvement efforts have stalled, Huang said.
Officials believe climate change is exacerbating the problem. Higher temperatures increase evaporation rates, raising concentrations of volatile organic compounds (VOCs) in the atmosphere. VOCs are a large group of chemicals that easily evaporate into the air and are released from sources ranging from vehicle exhaust and factories to paints and cleaning products.
Together with nitrogen oxides (NOx), VOCs act as ozone precursors, forming ozone through photochemical reactions that accelerate in hot conditions. NOx are gases mainly produced by fuel combustion in vehicles, power plants and industrial facilities.
Climate change is also leading to more stable atmospheric conditions and weaker winds, reducing vertical and horizontal dispersion and allowing ozone to accumulate, said Lung Shih-chun, deputy director of Academia Sinica’s Research Center for Environmental Changes.
To tackle ozone pollution, the ministry plans to strengthen controls not only on industrial facilities and vehicles, but also on consumer sources of VOCs such as building paints and household cleaning products.
“Volatile organic compounds come in many forms. They are emitted not just by industry and transport, but also from daily life, which makes them very difficult to regulate,” the environment ministry’s Huang said.
Separately, Taiwan will begin monitoring PM0.1, known as ultrafine particles, from 1 January, aligning with European Union standards. PM0.1 refers to particles smaller than 0.1 micrometres in diameter, which are far smaller than PM2.5 and can enter the bloodstream and organs more easily.
PM0.1 particles are far smaller than PM2.5 and have a much larger total surface area, making them more harmful to human health.
Yang Li-hao, a professor of occupational safety and health at China Medical University, described PM0.1 as a “Trojan horse” that can carry toxic substances deep into the body. The total surface area of PM0.1 is about 100 times that of the same mass of PM2.5, he said.
The EU has required member states to complete PM0.1 monitoring networks by the end of next year. Taiwan will set up three official monitoring stations in Taipei, Taichung and Tainan, along with three academic stations in Taipei and Kaohsiung, mainly in traffic hotspots where PM0.1 is often generated by tyre wear.
Taiwan began deploying a PM2.5 monitoring network in 2005, and air quality has improved since then. “Starting PM0.1 monitoring 20 years later can be seen as the beginning of a new generation of air quality governance,” Yang said.
Unlike PM2.5, which is measured by mass concentration, PM0.1 is so small and light that it is measured by particle number concentration, rather than weight. This counts the number of particles in a given volume of air instead of their total mass.
The WHO has yet to set formal standards, but suggests that average levels of around 20,000 particles per square centimetre per hour, or more than 10,000 over 24 hours, can be considered high.
