Urban forests are recognized as eco-friendly filters to reduce PM_2.5 concentrations. However, there remains a lack of consensus on how PM_2.5 affects forests’ productivity in highly polluted urban areas by altering solar radiation components. Here, we tested the hypothesis that the effects of PM_2.5 on the solar radiation components and forest productivity differ by season because of seasonal variations in solar elevation angle (β) and PM_2.5 concentrations. The PM_2.5 concentrations and CO₂ fluxes were measured using optical particle counters and an eddy covariance system, respectively, from April 2018 to December 2019 at a natural deciduous oak stand and an evergreen pine plantation in the peri‑urban region of the Seoul Metropolitan Area, Republic of Korea. Complex relationships among PM_2.5 concentration, direct radiation (S_dir), diffuse radiation (S_df), air temperature (T_a), and net ecosystem production (NEP) were disentangled by season and β using structural equation modeling. We found that the S_df was the controlling factor of NEP in both the stands, showing a more substantial effect than that of S_dir, T_a, and PM_2.5. In the oak stand, when oaks hold their leaves (May–October), the increase in PM_2.5 concentrations enhanced S_df and NEP, and it was more significant when β increased from 10 to 20° to > 60° However, in the pine plantation, the increase in PM_2.5 concentrations enhanced S_df and NEP when β > 40° and PM_2.5 < 10,100 cm^–3. In contrast, when β < 40° and PM_2.5 > 10,100 cm^–3, PM_2.5 increase resulted in a greater S_dir reduction than S_df enhancement, which consequently led to a NEP reduction. Our study results demonstrated the contrasting seasonal effects of PM_2.5 on solar radiation components and forest productivity and highlighted the importance of integrating them into ecosystem modeling and environment management plans in urban or peri‑urban regions.

_{城市森林被认为是降低 PM 2.5}浓度的环保过滤器。_{然而，对于 PM 2.5}如何通过改变太阳辐射成分来影响高度污染城市地区的森林生产力，仍然缺乏共识。在这里，我们检验了这样一个假设，即由于太阳仰角 ( β ) 和 PM _2.5浓度的季节性变化，PM _2.5对太阳辐射成分和森林生产力的影响因季节而异。PM _2.5浓度和 CO ₂从 2018 年 4 月到 2019 年 12 月，分别使用光学粒子计数器和涡流协方差系统在大韩民国首尔都市区周边地区的天然落叶橡树林和常绿松树种植园测量通量。_{PM 2.5}浓度、直接辐射 ( S _dir )、漫射辐射 ( S _df )、气温 ( T _a ) 和净生态系统产量 (NEP)之间的复杂关系通过季节和β使用结构方程模型解开。我们发现S _df是两个林分中 NEP 的控制因素，显示出比S更显着的影响_目录、T _a和 PM _2.5。在橡树林中，当橡树保持叶子时（5-10 月），PM _2.5浓度的增加增强了S _df和 NEP，并且当β从 10 到 20° 增加到 > 60°时更为显着。在人工林中，当β > 40° 且 PM _2.5 < 10,100 cm ^–3时，PM _2.5浓度的增加会增强S _df和 NEP 。相反，当β < 40° 和 PM _2.5 > 10,100 cm ^–3时，PM _2.5的增加导致更大的S _dir减少比S _df增强，因此导致 NEP 减少。我们的研究结果证明了 PM _2.5对太阳辐射成分和森林生产力的对比季节性影响，并强调了将它们纳入城市或城市周边地区的生态系统建模和环境管理计划的重要性。