The Chemistry of Atmosphere-Forest Exchange (CAFE) Model – Part 2: Application to BEARPEX-2007 observations
The Chemistry of Atmosphere-Forest Exchange (CAFE) Model – Part 2: Application to BEARPEX-2007 observations
复制标题
DOI：
10.5194/acp-11-1269-2011
复制
发表时间：
2010-09
影响因子：
6.3
通讯作者：
G. Wolfe;J. Thornton;N. Bouvier-Brown;A. Goldstein;J. Park;M. Mckay;D. Matross;J. Mao;W. Brune;B. LaFranchi;E. C. Browne;K. Min;P. Wooldridge;R. Cohen;J. Crounse;I. Faloona;J. Gilman;W. Kuster;J. Gouw;A. Huisman;F. Keutsch
中科院分区：
文献类型：
--
作者：
G. Wolfe;J. Thornton;N. Bouvier-Brown;A. Goldstein;J. Park;M. Mckay;D. Matross;J. Mao;W. Brune;B. LaFranchi;E. C. Browne;K. Min;P. Wooldridge;R. Cohen;J. Crounse;I. Faloona;J. Gilman;W. Kuster;J. Gouw;A. Huisman;F. Keutsch
在另一篇文章中，我们介绍了大气-森林交换化学(CAFE)模型，这是一个垂直分辨的一维化学传输模型，旨在探索近地表反应气体交换的细节。在这里，我们将CAFE应用于2007年生物圈对气溶胶的影响和光化学实验(BEARPEX-2007)的中午观测。在这项工作中，我们评估了CAFE建模方法，论证了冠层内化学对森林-大气交换的重要性，并指出了目前对冠层内过程理解的主要缺陷。CAFE通常重现BEARPEX-2007的观测结果，但需要增强的自由基循环机制，以克服在温暖(~29°C)期间观测到的羟基(OH)浓度被低估6倍的问题。模拟的过氧基硝酸酯(APN)通量对化学产生和损失的梯度非常敏感，这表明即使化学时间尺度相对于林冠混合时间尺度较长，化学也可能扰动森林-大气交换。在较温暖的条件下，模型将过氧乙酰硝酸盐(PAN)通量低估了50%，将交换速度低估了近三倍，这表明相对于源，近地表APN汇被低估了。硝酸通常在该地点的总干氮沉降量中占主导地位，但在较冷的条件下，其他活性氮(NO_Y)物种可占氮沉降量的28%。向上的NO2通量使冠层以上的净Ny通量比总沉积通量低约30%。CAFE对臭氧通量和交换速度的预测不足约20%。角质层和地面沉积参数的很大不确定性排除了非气孔通量归因于化学或表面吸收的决定性因素。对几种排放物种的垂直浓度梯度的模型测量比较表明，下层冠层空域可能只与上层冠层弱耦合。未来模拟森林-大气交换的努力将需要对非气孔沉积有更机械性的理解，并对冠层内混合过程有更彻底的描述。
In a companion paper, we introduced the Chemistry of Atmosphere-Forest Exchange (CAFE) model, a vertically-resolved 1-D chemical transport model designed to probe the details of near-surface reactive gas exchange. Here, we apply CAFE to noontime observations from the 2007 Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX-2007). In this work we evaluate the CAFE modeling approach, demonstrate the significance of in-canopy chemistry for forest-atmosphere exchange and identify key shortcomings in the current understanding of intra-canopy processes. CAFE generally reproduces BEARPEX-2007 observations but requires an enhanced radical recycling mechanism to overcome a factor of 6 underestimate of hydroxyl (OH) concentrations observed during a warm (~29 °C) period. Modeled fluxes of acyl peroxy nitrates (APN) are quite sensitive to gradients in chemical production and loss, demonstrating that chemistry may perturb forest-atmosphere exchange even when the chemical timescale is long relative to the canopy mixing timescale. The model underestimates peroxy acetyl nitrate (PAN) fluxes by 50% and the exchange velocity by nearly a factor of three under warmer conditions, suggesting that near-surface APN sinks are underestimated relative to the sources. Nitric acid typically dominates gross dry N deposition at this site, though other reactive nitrogen (NO_y) species can comprise up to 28% of the N deposition budget under cooler conditions. Upward NO_2 fluxes cause the net above-canopy NO_y flux to be ~30% lower than the gross depositional flux. CAFE under-predicts ozone fluxes and exchange velocities by ~20%. Large uncertainty in the parameterization of cuticular and ground deposition precludes conclusive attribution of non-stomatal fluxes to chemistry or surface uptake. Model-measurement comparisons of vertical concentration gradients for several emitted species suggests that the lower canopy airspace may be only weakly coupled with the upper canopy. Future efforts to model forest-atmosphere exchange will require a more mechanistic understanding of non-stomatal deposition and a more thorough characterization of in-canopy mixing processes.