Solar radiation plays a major role in atmospheric photochemistry, contributing to the formation and growth of ultrafine particles (PN). PN affect global Earth's radiation balance, climate system, and human health. However, the impact of solar activity on ambient PN remains unclear. In this study, we investigated the associations between daily ambient PN concentrations [particle number (PN)/cm³] and solar radio flux [solar activity index (F_10.7 in sfu)] as a solar activity parameter, shortwave solar radiation (SWR), daylight time (DL), cosmic ray-induced ionization (CRII), and air pollution [PM_2.5, black carbon (BC) and SO₂] over a 19-year period in Boston, MA. We used generalized additive models adjusted for local environmental conditions. We found that F_10.7 was the strongest predictor for daily PN concentrations over all time lags (0–28 days of lags) and seasons. The effects were higher in winter and fall. In winter, an interquartile (IQR) of 60 sfu F_10.7 corresponded to an increase of 5770 PN/cm³ in the day of PN collection. In fall, an IQR of 75.5 sfu F_10.7 was associated with an increase of 5429 PN/cm³. The effects of F_10.7 on PN concentrations were slightly greater when the models were adjusted for air pollution. In summer, ambient PN concentrations were statistically significantly associated with F_10.7, SWR, and BC, with the strongest association found for PN and BC in the day of PN collection. Unlike the effects of F_10.7, SWR and local pollutants on PN concentrations, DL and CRII were negatively associated with ambient PN in the analyses. These findings suggest that solar activity may have a significant impact on daily ambient PN concentrations that affect the Earth's climate system and human health.

太阳辐射在大气光化学中起着重要作用，有助于超细颗粒 (PN) 的形成和生长。PN 影响全球地球的辐射平衡、气候系统和人类健康。然而，太阳活动对环境 PN 的影响仍不清楚。在这项研究中，我们调查了日常环境PN浓度之间的关联[粒子数（PN）/厘米³ ]和太阳能无线电通量[太阳活动指数（˚F _10.7在SFU）]作为太阳活动参数，短波太阳辐射（SWR） 、日光时间 (DL)、宇宙射线诱导电离 (CRII) 和空气污染 [PM _2.5、黑碳 (BC) 和 SO ₂] 在马萨诸塞州波士顿的 19 年期间。我们使用根据当地环境条件调整的广义加性模型。我们发现F _10.7是所有时间滞后（滞后 0-28 天）和季节中每日 PN 浓度的最强预测因子。冬季和秋季的影响更大。在冬季，60 sfu F _10.7的四分位间距 (IQR)对应于PN 收集当天的5770 PN/cm ³增加。在秋季，75.5 sfu F _10.7的 IQR与 5429 PN/cm ³的增加有关。F _10.7的影响当模型针对空气污染进行调整时，对 PN 浓度的影响略大。在夏季，环境 PN 浓度与F _10.7、SWR 和 BC在统计上显着相关，在 PN 收集当天发现的 PN 和 BC 关联最强。与F _10.7、SWR 和局部污染物对 PN 浓度的影响不同，在分析中，DL 和 CRII 与环境 PN 呈负相关。这些发现表明，太阳活动可能对影响地球气候系统和人类健康的每日环境 PN 浓度产生重大影响。