In the northern hemisphere, boreal forests are a major source of biogenic volatile organic compounds (BVOCs), which drive atmospheric processes and lead to cloud formation and changes in the Earth’s radiation budget. Although forest vegetation is known to be a significant source of BVOCs, the role of soil and the forest floor, and especially interannual variations in fluxes, remains largely unknown due to a lack of long-term measurements. Our aim was to determine the interannual, seasonal and diurnal dynamics of boreal forest floor volatile organic compound (VOC) fluxes and to estimate how much they contribute to ecosystem VOC fluxes. We present here an 8-year data set of forest floor VOC fluxes, measured with three automated chambers connected to the quadrupole proton transfer reaction mass spectrometer (quadrupole PTR-MS). The exceptionally long data set shows that forest floor fluxes were dominated by monoterpenes and methanol, with relatively comparable emission rates between the years. Weekly mean monoterpene fluxes from the forest floor were highest in spring and in autumn (maximum 59 and 86 μg m-2 h-1, respectively), whereas the oxygenated VOC fluxes such as methanol had highest weekly mean fluxes in spring and summer (maximum 24 and 79 μg m-2 h-1, respectively). Although the chamber locations differed from each other in emission rates, the inter-annual dynamics were very similar and systematic. Accounting for this chamber location dependent variability, temperature and relative humidity, a mixed effects linear model was able to explain 79–88% of monoterpene, methanol, acetone, and acetaldehyde fluxes from the boreal forest floor. The boreal forest floor was a significant contributor in the forest stand fluxes, but its importance varies between seasons, being most important in autumn. The forest floor emitted 2–93% of monoterpene fluxes in spring and autumn and 1–72% of methanol fluxes in spring and early summer. The forest floor covered only a few percent of the forest stand fluxes in summer.
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机译：在北半球，北方森林是生物挥发性有机化合物（BVOC）的主要来源，它驱动大气过程并导致云的形成和地球辐射预算的变化。尽管已知森林植被是BVOC的重要来源，但由于缺乏长期测量，土壤和森林地面的作用，尤其是通量的年际变化仍然未知。我们的目的是确定北方森林地表挥发性有机化合物（VOC）通量的年际，季节和昼夜动态，并估算它们对生态系统VOC通量的贡献。我们在这里展示了一个为期8年的森林地面VOC通量数据集，该数据集是通过连接到四极质子转移反应质谱仪（quadrupole PTR-MS）的三个自动室测量的。异常长的数据集表明，林地通量主要由单萜和甲醇构成，年间的排放率相对可比。春季和秋季，森林地面的单萜平均每周通量最高（分别为最大59和86μgm -2 h -1 ），而氧化的VOC通量例如甲醇在春季和夏季具有最高的每周平均通量（分别为24和79μgm -2 h -1 ）。尽管各室的排放速率互不相同，但年度动态却非常相似且系统。考虑到该室位置相关的可变性，温度和相对湿度，一个混合效应线性模型能够解释来自北方森林地表的单萜烯，甲醇，丙酮和乙醛通量的79–88％。北方森林地表是林分通量的重要贡献，但其重要性随季节而变化，在秋季尤为重要。在春季和秋季，森林地表排放了2–93％的单萜类通量，在春季和初夏排放了1–72％的甲醇。夏季，森林地面仅覆盖了林分通量的百分之几。
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