Air-Parcel Residence Times Within Forest Canopies
Air-Parcel Residence Times Within Forest Canopies
复制标题
航空包裹在森林冠层内的停留时间
DOI：
10.1007/s10546-017-0269-7
复制
发表时间：
2017
影响因子：
4.3
通讯作者：
J. Fuentes
中科院分区：
文献类型：
--
作者：
T. Gerken;M. Chamecki;J. Fuentes
基于一个简单的湍流扩散模型和一级化学动力学模型，我们提出了一个理论模型来确定中性条件下气团停留时间和林冠外释放的反应气体。在中性层结条件下，将气团停留时间的理论预测值与大涡模拟得到的值进行了比较。气团停留时间的中位数从上冠层的几秒到接近地面的约30分钟不等，在下冠层的停留时间分布偏向较长的时间。理论模型和大涡模拟得到的概率密度函数吻合较好，而理论模型只需要冠层高度和冠层内部涡散系数的信息。建立的涡旋扩散系数模型还需要冠层顶部的摩擦速度和垂直速度标准差的参数化剖面。气团停留时间的理论模型被扩展到包括植物排放的碳氢化合物的达姆克勒数(Da)范围内的一级化学反应。由此得到的林冠外输出分数范围从接近1的$$Da=10^{-3}$$Da=10-3到小于0.3的$$Da=10$$Da=10。这些结果强调了在计算反应性痕量气体的林冠外输出分数时考虑气团停留时间的影响的必要性。
We present a theoretical model, based on a simple model of turbulent diffusion and first-order chemical kinetics, to determine air-parcel residence times and the out-of-canopy export of reactive gases emitted within forest canopies under neutral conditions. Theoretical predictions of the air-parcel residence time are compared to values derived from large-eddy simulation for a range of canopy architectures and turbulence levels under neutral stratification. Median air-parcel residence times range from a few sec in the upper canopy to approximately 30 min near the ground and the distribution of residence times is skewed towards longer times in the lower canopy. While the predicted probability density functions from the theoretical model and large-eddy simulation are in good agreement with each other, the theoretical model requires only information on canopy height and eddy diffusivities inside the canopy. The eddy-diffusivity model developed additionally requires the friction velocity at canopy top and a parametrized profile of the standard deviation of vertical velocity. The theoretical model of air-parcel residence times is extended to include first-order chemical reactions over a range of of Damköhler numbers (Da) characteristic of plant-emitted hydrocarbons. The resulting out-of-canopy export fractions range from near 1 for $$Da =10^{-3}$$Da=10-3 to less than 0.3 at $$Da = 10$$Da=10. These results highlight the necessity for dense and tall forests to include the impacts of air-parcel residence times when calculating the out-of-canopy export fraction for reactive trace gases.
影响因子：
3.7
作者：
Pan, Y.;Chamecki, M.
通讯作者：
Chamecki, M.