1a:I[76865,["/_next/static/chunks/d07a36b34c614bac.js","/_next/static/chunks/a439560253821848.js","/_next/static/chunks/992d80515d7f780d.js","/_next/static/chunks/3adfb55b15c8d19c.js","/_next/static/chunks/b642b3e65e2c6231.js","/_next/static/chunks/fc50eca1ad01dc11.js","/_next/static/chunks/afc6bdd59b458409.js","/_next/static/chunks/6448cccc5d968256.js"],"Grid"] 1b:I[17291,["/_next/static/chunks/d07a36b34c614bac.js","/_next/static/chunks/a439560253821848.js","/_next/static/chunks/992d80515d7f780d.js","/_next/static/chunks/3adfb55b15c8d19c.js","/_next/static/chunks/b642b3e65e2c6231.js","/_next/static/chunks/fc50eca1ad01dc11.js","/_next/static/chunks/afc6bdd59b458409.js","/_next/static/chunks/6448cccc5d968256.js"],"GridCol"] 1c:I[34616,["/_next/static/chunks/d07a36b34c614bac.js","/_next/static/chunks/a439560253821848.js","/_next/static/chunks/992d80515d7f780d.js","/_next/static/chunks/3adfb55b15c8d19c.js","/_next/static/chunks/b642b3e65e2c6231.js","/_next/static/chunks/fc50eca1ad01dc11.js","/_next/static/chunks/afc6bdd59b458409.js","/_next/static/chunks/6448cccc5d968256.js"],"Avatar"] 1d:I[32972,["/_next/static/chunks/d07a36b34c614bac.js","/_next/static/chunks/a439560253821848.js","/_next/static/chunks/992d80515d7f780d.js","/_next/static/chunks/3adfb55b15c8d19c.js","/_next/static/chunks/b642b3e65e2c6231.js","/_next/static/chunks/fc50eca1ad01dc11.js","/_next/static/chunks/afc6bdd59b458409.js","/_next/static/chunks/6448cccc5d968256.js"],"default"] 1e:T513,Ultrafine particles (UFPs) under 100 nm pose significant health risks inadequately addressed by traditional mass-based metrics. The WHO emphasizes particle number concentration (PNC) for assessing UFP exposure, but large-scale evaluations remain scarce. In this study, we developed a stacking-based machine learning framework integrating data-driven and physical-chemical models for a national-scale UFP exposure assessment at 1 km spatial and 1-hour temporal resolutions, leveraging long-term standardized PNC measurements in Switzerland. Approximately 20% (1.7 million) of the Swiss population experiences high UFP exposure exceeding an annual mean of 10⁴ particles‧cm^-3, with a national average of (9.3 ± 4.7)×10³ particles‧cm^-3, ranging from (5.5 ± 2.3)×10³ (rural) to (1.4 ± 0.5)×10⁴ particles‧cm^-3 (urban). A nonlinear relationship is identified between the WHO-recommended 1-hour and 24-hour exposure reference levels, suggesting their non-interchangeability. UFP spatial heterogeneity, quantified by coefficient of variation, ranges from 4.7 ± 4.2 (urban) to 13.8 ± 15.1 (rural) times greater than PM_2.5. These findings provide crucial insights for the development of future UFP standards.

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