About Ambient Ultrafine Particles
This article is a summary of the White paper Ambient ultra-fine particles: evidence for policymakers. What are ultra-fine particles, why are they important, and what is the challenge? The white paper dives into the current state of knowledge concerning exposure, toxicology, epidemiology and current regulations. I have written a short introduction:
An ultrafine particle is a particle sized bout 100nm in diameter or less. The same definition applies to a nanoparticle. UFP constitutes a somewhat arbitrary classification of particles in terms of their size because there is no objective natural division between UFP and lager particles. As UFP have little mass, their concentrations are most commonly measures and expressed in terms of particle number concentration (PNC) per unit volume of air (the number of particles per cubic cm). In contrast, larger particles (f.a. PM 2.5 and lager) are measured in terms of mass concentration (microgram per cubic meter). The term UFP is often uses loosely, meaning various ranges of PNC in the submicrometer range.
They come from vehicle exhaust, aviation, shipping, power plants, industry, residential heating, and indoor sources such as cooking and burning candles. They can also form in the atmosphere from gases under sunlight.
Why are UFP important?
- Health risks: UFP penetrate deep into the lungs, enter the bloodstream, and can trigger inflammation and cardiovascular, respiratory, and developmental problems. They may cause harm even when PM2.5/PM10 levels are low.
- Environmental risks: UFP can act as seeds for cloud formation, influencing rainfall and climate.
Why are they a challenge?
- Science: Monitoring UFP requires costly instruments and there is no standard method. Their short lifetime and large variation across space and time make measurements difficult.
- Policy: Current air quality laws focus on PM2.5/PM10 mass, not UFP. Measures that reduce PM mass may not reduce UFP and in some cases even can increase them.
What We Know
- Exposure:
- UFP levels in clean environments: <1,000 particles/cm³.
- Urban background: <10,000 particles/cm³.
- Near traffic or during new particle formation, levels can spike far higher.
- Indoor levels are often dominated by cooking and other household sources.
- Health impacts (Toxicology):
- UFP can be more harmful per unit mass than larger particles.
- Toxicity depends on particle source and composition.
- Short high exposures may be as important as long-term averages.
- Epidemiology:
- Studies link UFP to health problems, but results vary because sources, climates, and measurement methods differ.
- More systematic studies and standardized monitoring are needed.
- Regulation:
- Reducing PM2.5/PM10 alone will not guarantee UFP reduction.
- Black carbon controls help, but not all UFP are eliminated.
- Long-term monitoring at selected ‘super sites’ and source-specific control (traffic, biomass burning, aviation) is needed.
Key messages for policymakers
- UFP are a distinct pollutant – they need to be regulated separately from PM2.5/PM10.
- Health and climate impacts are significant. UFP can worsen disease burden and alter weather patterns.
- Better monitoring is essential, Standardization and investment in long-term UFP monitoring sites are needed.
- Source control works. Especially for transport, biomass burning.
- Indoor exposure matters. Stricter ventilation and emission controls in buildings are important.
The above summary is derived from the White paper Ambient Ultra-fine Particles: evidence for policymakers. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License.
