Abstract Urban trees provide natural shade and moderate human exposure to solar ultraviolet radiation. To date, most studies quantifying UV attenuation by urban tree canopies have taken place in Australia, with no studies in North America. Few studies have utilized sensors sensitive to UV-B radiation, although the shorter wavelengths are more important in determining erythemal (skin burning) UV. We collected solar UV radiation exposure data beneath 64 individuals of 16 tree species commonly planted in the City of Toronto's schoolyards and public parks, using UV electronic logging dosimeters that have a spectral response closely matching the erythemal action spectrum. Additional data were collected on canopy structure (crown radii, crown transparency, crown depth, diameter at breast height, height to live crown, and leaf-level data). UV protection factor (PF: the ratio of open-site UV to below-canopy UV) varied 2.6-fold among species, ranging from ∼1.3−3.4. Statistical models for variation among trees indicated that crown transparency (%), the ratio of crown breadth to height to live crown, and species shade tolerance were important predictors of PF. Acer platanoides ‘Crimson King’, Celtis occidentalis L., Quercus bicolor Willd., and Fagus sylvatica ‘Purpurea’ showed the highest PF values (>3), and Ginkgo biloba L. and Acer rubrum L. showed the lowest PF values (

中文翻译：

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城市公共空间阔叶针叶树紫外线防护因子评价

摘要 城市树木为人类提供自然遮荫和适度的太阳紫外线辐射。迄今为止，大多数量化城市树冠紫外线衰减的研究都是在澳大利亚进行的，但没有在北美进行研究。很少有研究使用对 UV-B 辐射敏感的传感器，尽管较短的波长在确定红斑（皮肤灼伤）紫外线方面更为重要。我们使用光谱响应与红斑作用光谱密切匹配的紫外线电子测井剂量计，收集了多伦多市校园和公园中常见种植的 16 种树种的 64 个人下的太阳紫外线辐射暴露数据。收集了有关冠层结构的其他数据（冠半径、冠透明度、冠深、胸高直径、活冠高度和叶级数据）。紫外线防护系数（PF：开放场地紫外线与冠层紫外线的比率）在物种之间变化 2.6 倍，范围为~1.3-3.4。树木间变异的统计模型表明，树冠透明度 (%)、树冠宽度与高度与活树冠的比率以及物种耐荫性是 PF 的重要预测因子。Acer platanoides 'Crimson King'、Celtis occidentalis L.、Quercus bicolor Willd. 和 Fagus sylvatica 'Purpurea' 的 PF 值最高（>3），而 Ginkgo biloba L. 和 Acer rubrum L. 的 PF 值最低（