Forest-atmosphere exchange of ozone: sensitivity to very reactive biogenic VOC emissions and implications for in-canopy photochemistry
Forest-atmosphere exchange of ozone: sensitivity to very reactive biogenic VOC emissions and implications for in-canopy photochemistry
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DOI：
10.5194/acp-11-7875-2011
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发表时间：
2011-08
影响因子：
6.3
通讯作者：
G. Wolfe;J. Thornton;M. Mckay;A. Goldstein
中科院分区：
文献类型：
--
作者：
G. Wolfe;J. Thornton;M. Mckay;A. Goldstein
抽象的。了解森林环境内部和上方臭氧的归宿对于评估人类活动对城乡交界处生态系统和空气质量的影响至关重要。观测到的森林-大气臭氧交换速度往往比仅用气孔吸收所能解释的要快得多，这表明树冠层内存在额外的臭氧汇。使用大气-森林交换化学（CAFE）模型，结合2007年生物圈对气溶胶和光化学实验（BEARPEX-2007）的夏季中午观测，我们探讨了臭氧分解非常活跃但尚未识别的生物挥发性有机化合物（BVOC）可能影响森林-大气臭氧交换的假设的可行性和影响。非气孔过程通常产生67%的观测到的臭氧通量，但臭氧与测得的BVOC，包括单萜和倍半萜的反应，可以只占2%的流量在选定的时间范围内。通过纳入额外的排放和化学代理非常活泼的挥发性有机化合物（VRVOC），经历快速臭氧分解，我们证明，在冠层化学臭氧汇~2 × 108 molec cm−3 s−1可以关闭臭氧通量预算。即使在这种情况下，臭氧的65分钟化学寿命也比约2分钟的冠层停留时间长得多，这突出表明，即使化学反应相对于垂直混合“缓慢”，化学反应也会影响反应性痕量气体交换。这种VRVOC臭氧分解水平可以使OH和RO 2的产量增加多达1 pptv s-1，并根据实际产品产量显著改变它们各自的垂直分布。反应产物也会对氧化的挥发性有机化合物的收支产生重大影响，进而对二次有机气溶胶质量产生重大影响。考虑到化学臭氧通量对冠层内化学和臭氧沉积估计的潜在重大影响，今后的工作应侧重于量化森林内的臭氧反应性和非气孔（如表皮）沉积。
Abstract. Understanding the fate of ozone within and above forested environments is vital to assessing the anthropogenic impact on ecosystems and air quality at the urban-rural interface. Observed forest-atmosphere exchange of ozone is often much faster than explicable by stomatal uptake alone, suggesting the presence of additional ozone sinks within the canopy. Using the Chemistry of Atmosphere-Forest Exchange (CAFE) model in conjunction with summer noontime observations from the 2007 Biosphere Effects on Aerosols and Photochemistry Experiment (BEARPEX-2007), we explore the viability and implications of the hypothesis that ozonolysis of very reactive but yet unidentified biogenic volatile organic compounds (BVOC) can influence the forest-atmosphere exchange of ozone. Non-stomatal processes typically generate 67 % of the observed ozone flux, but reactions of ozone with measured BVOC, including monoterpenes and sesquiterpenes, can account for only 2 % of this flux during the selected timeframe. By incorporating additional emissions and chemistry of a proxy for very reactive VOC (VRVOC) that undergo rapid ozonolysis, we demonstrate that an in-canopy chemical ozone sink of ~2 × 108 molec cm−3 s−1 can close the ozone flux budget. Even in such a case, the 65 min chemical lifetime of ozone is much longer than the canopy residence time of ~2 min, highlighting that chemistry can influence reactive trace gas exchange even when it is "slow" relative to vertical mixing. This level of VRVOC ozonolysis could enhance OH and RO2 production by as much as 1 pptv s−1 and substantially alter their respective vertical profiles depending on the actual product yields. Reaction products would also contribute significantly to the oxidized VOC budget and, by extension, secondary organic aerosol mass. Given the potentially significant ramifications of a chemical ozone flux for both in-canopy chemistry and estimates of ozone deposition, future efforts should focus on quantifying both ozone reactivity and non-stomatal (e.g. cuticular) deposition within the forest.