Ultrafine Particle Concentrations in Urban Environments

Ultrafine particles (UFPs), defined as airborne aerosols with diameters below 0.1 µm, are pervasive in cities and arise predominantly from combustion sources, photochemical reactions and industrial activities. Their small size affords high number concentrations and large surface-to-mass ratios, enhancing chemical reactivity and the capacity to carry adsorbed toxins deep into the respiratory tract. In urban settings, motor vehicle emissions, particularly from diesel engines, dominate UFP levels, but emerging evidence highlights the role of atmospheric nucleation events driven by volatile organic compounds and sulphur gases under strong sunlight. Spatial and temporal variability in UFP concentrations reflects traffic patterns, meteorology and urban morphology, complicating exposure assessment. Health concerns centre on cardiovascular and pulmonary effects, with epidemiological associations between UFP exposure and inflammation, oxidative stress and exacerbations of chronic disease. Advances in monitoring technology, including scanning mobility particle sizers and mobile sensor networks, now enable high‐resolution mapping of particle number concentrations. Improved understanding of UFP sources, transformation and human exposure pathways underpins the design of targeted mitigation strategies, from low-emission traffic zones to urban greening, that aim to reduce public health burdens worldwide.

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Ultrafine Particle Concentrations in Urban Environments publication trend

The graph below shows the total number of articles in ultrafine particle concentrations in urban environments across all publications each year (not limited to Nature Index journals).

Technical terms

Ultrafine particle (UFP): An aerosol particle with an aerodynamic diameter smaller than 0.1 µm, characterised by high number concentration and surface area.

Particle number concentration (PNC): The count of particles per unit volume of air, typically expressed in particles cm⁻³, used to quantify UFP exposure.

New particle formation (NPF): Atmospheric process in which gaseous precursors nucleate and grow into stable ultrafine particles under suitable conditions of vapour saturation and low pre-existing particle surface area.

Positive Matrix Factorisation (PMF): A statistical receptor-modelling technique that deconvolutes observed particle number size distributions into contributing source factors without prior source profiles.

References

1. Ultrafine particles: unique physicochemical properties relevant to health and disease. Experimental & Molecular Medicine (2020).
2. Sources, characteristics, toxicity, and control of ultrafine particles: An overview. Geoscience Frontiers (2022).
3. Ultrafine particles in cities. Environment International (2014).
4. Exposure Assessment for Atmospheric Ultrafine Particles (UFPs) and Implications in Epidemiologic Research. Environmental Health Perspectives (2005).
5. Traffic and nucleation events as main sources of ultrafine particles in high-insolation developed world cities. Atmospheric Chemistry and Physics (2015).
6. Source apportionment of particle number size distribution in urban background and traffic stations in four European cities. Environment International (2019).