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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Protonation and oligomerization of gaseous isoprene on mildly acidic surfaces: Implications for atmospheric chemistry
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Protonation and oligomerization of gaseous isoprene on mildly acidic surfaces: Implications for atmospheric chemistry

机译：轻度酸性表面上气态异戊二烯的质子化和低聚：对大气化学的影响

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In a global process linking the Earth's climate with its ecosystems, massive photosynthetic isoprene (ISOP) emissions are converted to light-scattering haze. This phenomenon is imperfectly captured by atmospheric chemistry models: predicted ISOP emissions atop forest canopies would deplete the oxidizing capacity of the overhead atmosphere, at variance with field observations. Here we address this key issue in novel laboratory experiments where we apply electrospray mass spectrometry to detect online the products of the reactive uptake of gaseous ISOP on the surface of aqueous jets as a function of acidity. We found that ISOP is already protonated to ISOPH ~+ and undergoes cationic oligomerization to (ISOP) _2H ~+ and (ISOP) _3H ~+ on the surface of pH < 4 water jets. We estimate uptake coefficients, γ _(ISOP) = (0.5 - 2.0) × 10 ~(-6) on pH = 3 water, which translate into the significant reuptake of leaf-level ISOP emissions in typical (surface-to-volume ～5 m ~(-1)) forests during realistic (a few minutes) in-canopy residence times. Our findings may also account for the rapid decay of ISOP in forests after sunset and help bring the global budget of volatile organic compounds closer to balance.
机译：在将地球的气候与其生态系统联系起来的全球过程中，大量的光合作用异戊二烯（ISOP）排放物转化为光散射的薄雾。大气化学模型不能完美地捕捉到这种现象：森林冠层上的ISOP排放量预计会耗尽高架大气层的氧化能力，这与现场观测结果有所不同。在这里，我们在新颖的实验室实验中解决了这个关键问题，在该实验中，我们应用电喷雾质谱技术来在线检测水性喷射器表面上气态ISOP的反应性吸收随酸度变化的产物。我们发现，ISOP已质子化为ISOPH〜+，并且在pH <4的水射流表面上发生阳离子低聚反应，生成（ISOP）_2H〜+和（ISOP）_3H〜+阳离子。我们估计在pH = 3的水上的吸收系数，γ_（ISOP）=（0.5-2.0）×10〜（-6），这转化为典型（表面到体积〜在实际的（几分钟）树冠居住时间内需要5 m〜（-1））的森林。我们的发现还可能解释了日落之后森林中ISOP的快速衰减，并有助于使挥发性有机化合物的全球预算更趋于平衡。

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