The epidemiological evidence for ultrafine particles (UFP; particles with diameter <100 nm) causing chronic health effects independent of fine particulate matter (PM_2.5) mass is inconclusive. A prevailing view is that urban UFP and PM_2.5 mass have different spatial patterns, which should allow epidemiological studies to distinguish their independent, chronic health effects. We investigate intraurban spatial correlation of PM_2.5 and UFP exposures in Pittsburgh, Pennsylvania. Measurements and predictions of a land-use regression model indicate moderate spatial correlation between particle number concentrations (PNC; a proxy for UFP) and PM_2.5 (R² of 0.38 and 0.41, respectively). High-resolution (1-km) chemical transport model simulations predict stronger spatial correlation (R² ≈ 0.8). The finding of moderate to strong spatial correlation was initially surprising because secondary aerosol contributes the vast majority of PM_2.5 mass. However, intraurban spatial patterns of both PNC and PM_2.5 are driven by local emissions and both pollutants largely behave as passive tracers at time scales of 1 day or less required for transport across most urban environments. Although previous research has shown little temporal correlation between PNC and PM_2.5, our finding of moderate to strong spatial correlation may complicate epidemiological analyses to separate the chronic health effects of PNC from PM_2.5 mass.

中文翻译：

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城市规模的超细颗粒数量与细颗粒质量的空间相关性：对健康评估的意义。

关于超细颗粒（UFP；直径<100 nm的颗粒）引起慢性健康影响的流行病学证据尚无定论，这与细小颗粒物质（PM _2.5）无关。普遍的看法是，城市UFP和PM _2.5的质量具有不同的空间格局，这应允许流行病学研究区分其独立的慢性健康影响。我们调查宾夕法尼亚州匹兹堡的PM _2.5和UFP暴露的城市内部空间相关性。土地利用回归模型的测量和预测表明，颗粒物浓度（PNC； UFP的替代物）和PM _2.5（R ²分别为0.38和0.41）。高分辨率（1公里）的化学品运输模型模拟预测更强的空间相关性（- [R ² ≈0.8）。起初令人惊讶的是发现了中等至强烈的空间相关性，因为次级气溶胶占了PM _2.5质量的绝大部分。但是，PNC和PM _2.5的城市内部空间格局都是由局部排放驱动的，并且在大多数城市环境中运输所需的1天或更短的时间内，两种污染物在很大程度上都充当被动示踪剂。尽管先前的研究表明PNC和PM _2.5之间的时间相关性很小，我们发现中度到强空间相关性可能会使流行病学分析复杂化，从而将PNC的慢性健康影响与PM _2.5质量区分开。