Seasonal Flux Measurements over a Colorado Pine Forest Demonstrate a Persistent Source of Organic Acids
Seasonal Flux Measurements over a Colorado Pine Forest Demonstrate a Persistent Source of Organic Acids
复制标题
DOI：
10.1021/acsearthspacechem.9b00182
复制
发表时间：
2019-09-19
影响因子：
3.4
通讯作者：
Farmer, Delphine K.
中科院分区：
文献类型：
--
作者：
Fulgham, S. Ryan;Brophy, Patrick;Farmer, Delphine K.
森林既可以是大气中挥发性有机化合物的来源，也可以是汇。由于多种模型测量比较报告了甲酸来源缺失，人们对森林在控制有机酸浓度方面所发挥的作用仍然知之甚少。 2016 年，我们对科罗拉多州黄松林中氧化挥发性有机化合物的浓度和涡流协方差通量进行了季节性测量。昼夜浓度分布显示中午达到最大值，这与之前的研究一致。我们观察到松林中的甲酸、丙酸、甲基丙烯酸和丁酸在所有季节都有持续但变化的向上通量。甲酸浓度和通量比其他有机酸高 10 倍，白天交换速度约为 4-6 cm s(-1)。其他有机酸在温暖季节具有与甲酸相似的交换速度，而在寒冷季节则具有小得多的交换速度。所有有机酸的向上通量随温度呈指数增加。观察到的净向上通量表明，干沉积小于有机酸的生态系统来源。与树冠内化学的估计相比，土壤和松树的初级排放量很小。我们的研究指出有机酸的生态系统来源被低估（例如，大型或多功能萜类化合物的树冠内化学），高估的干沉积汇（可能由于干旱环境）和/或上边界层中有机酸的未解决的汇。在温暖的季节，森林是大气有机酸的潜在重要来源，但有必要进一步研究干沉降机制和树冠内化学。
Forests can be both sources and sinks of volatile organic compounds to the atmosphere. The role that forests play in controlling organic acid concentrations remains poorly understood with multiple model-measurement comparisons reporting missing sources of formic acid. We conducted seasonal measurements of concentrations and eddy covariance fluxes of oxidized volatile organic compounds over a ponderosa pine forest in Colorado in 2016. Diel concentration profiles show mid-day maxima, consistent with previous studies. We observed persistent but variable upward fluxes of formic, propionic, methacrylic, and butyric acids from the pine forest during all seasons. Formic acid concentrations and fluxes were similar to 10 times higher than the other organic acids with daytime exchange velocities on the order of 4-6 cm s(-1). The other organic acids had similar exchange velocities as formic acid in the warmer seasons and much smaller exchange velocities in the colder seasons. The upward fluxes for all organic acids increased exponentially with temperature. The observed net upward flux demonstrated that dry deposition was smaller than ecosystem sources of the organic acids. Primary emissions from soil and pine trees were small, in contrast to estimates of in-canopy chemistry. Our study points to an underestimated ecosystem source of organic acids (e.g., in-canopy chemistry of large or multifunctional terpenoids), an overestimated dry deposition sink (potentially due to the arid environment), and/or an unresolved sink of organic acids in the upper boundary layer. Forests are potentially large sources of atmospheric organic acids in warmer seasons but further investigation into dry deposition mechanisms and in-canopy chemistry is warranted.