Ultrafine particles (UFPs) pose a human health risk as they can penetrate deep into the respiratory system. The Harvard supersite in Boston, MA provides one of the longest time series of UFP concentrations. This study examined the hypothesis that long-term reductions in PM_2.5 mass and sulfur have influenced UFP trends by limiting the ability of UFPs to coagulate onto the accumulation mode via polydisperse coagulation with larger particles. The study used Generalized Additive Models (GAMs) to assess whether changes in PM_2.5 mass and sulfur concentrations resulted in smaller than expected (assuming no change in PM_2.5 mass or sulfur) decreases in daily UFP trends over the 20-year period from 1999 to 2018. The impact of PM_2.5 mass and sulfur changes were represented as UFP penalties. Bootstrapping was applied to calculate standard errors for the different trend and penalty estimates. Results showed that PM_2.5 mass and sulfur concentrations declined significantly over the study period. The analysis found an estimated 7.3% (95% CI: 3.5, 11.1%) UFP penalty due to long-term PM_2.5 mass trends, and a 9.9% (95% CI: 6.2, 13.7%) UFP penalty due to long-term sulfur trends. Findings from this study suggest that future UFP control efforts should account for the role of PM_2.5 mass and sulfur changes.

Implications

Using one of the longest available time series of UFP concentrations (1999 to 2018), this study examined the hypothesis that long-term trends of PM_2.5 mass and sulfur concentrations have an impact on UFP trends. We found that PM_2.5 mass and sulfur reductions had a small but significant impact, i.e., penalty, on UFP trends. Improved understanding of the impact of PM_2.5 mass and sulfur concentrations on UFP trends can inform future air quality control efforts.

中文翻译：

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从1999年到2018年，PM2.5的质量和硫的减少对马萨诸塞州波士顿市超细颗粒趋势的长期影响。

超细颗粒（UFP）可能会深入呼吸系统，因此对人类健康构成威胁。马萨诸塞州波士顿市的哈佛超级站点提供了UFP浓度最高的时间序列之一。这项研究检验了以下假设：PM _2.5质量和硫的长期减少通过限制UFP通过较大颗粒的多分散凝结而凝结到堆积模式的能力，影响了UFP趋势。该研究使用通用添加剂模型（GAM）评估了从1999年到20年间20年间每日UFP趋势的减少，PM _2.5质量和硫浓度的变化是否导致小于预期（假设PM _2.5质量或硫没有变化）的降低。 2018 PM的影响_2.5质量和硫的变化表示为UFP处罚。采用自举法来计算不同趋势和惩罚估计的标准误差。结果表明，在研究期间，PM _2.5的质量和硫浓度显着下降。该分析发现，由于长期PM _2.5质量趋势，估计UFP罚金为7.3％（95％CI：3.5，11.1％），由于长期PM2.9质量趋势，有9.9％（95％CI：6.2，13.7％）UFP罚金硫的趋势。这项研究的结果表明，未来的UFP控制工作应说明PM _2.5的质量和硫含量变化的作用。

含义

本研究使用UFP浓度的最长可用时间序列之一（1999年至2018年），检验了以下假设：PM _2.5质量和硫浓度的长期趋势会影响UFP趋势。我们发现，减少PM _2.5的质量和减少硫含量对UFP趋势影响不大，但影响显着。更好地了解PM _2.5的质量和硫浓度对UFP趋势的影响可以为将来的空气质量控制工作提供参考。