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Variability of CO_2 concentrations and fluxes in and above an urban street canyon

机译：城市街道峡谷内外的CO_2浓度和通量的变化

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摘要

The variability of CO_2 concentrations and fluxes in dense urban environments is high due to the inherent heterogeneity of these complex areas and their spatio-temporally variable anthropogenic sources. With a focus on micro- to local-scale CO_2-exchange processes, measurements were conducted in a street canyon in the city of Basel, Switzerland in 2010. CO_2 fluxes were sampled at the top of the canyon (19 m) and at 39 m while vertical CO_2 concentration profiles were measured in the center and at a wall of the canyon. CO_2 concentration distributions in the street canyon and exchange processes with the layers above show, apart from expected general diurnal patterns due mixing layer heights, a strong dependence on wind direction relative to the canyon. As a consequence of the resulting corkscrew-like canyon vortex, accumulation of CO_2 inside the canyon is modulated with distinct distribution patterns. The evaluation of diurnal traffic data provides good explanations for the vertical and horizontal differences in CO_2-dis-tribution inside the canyon. Diurnal flux characteristics at the top of the canyon can almost solely be explained with traffic density expressed by the strong linear dependence. Even the diurnal course of the flux at 39 m shows a remarkable relationship to traffic density for east wind conditions while, for west wind situations, a change toward source areas with lower emissions leads to a reduced flux.
机译：由于这些复杂区域的固有异质性及其时空变化的人为来源，在稠密的城市环境中，CO_2浓度和通量的变化性很高。着眼于微尺度到局部尺度的CO_2交换过程，2010年在瑞士巴塞尔市的一个街道峡谷中进行了测量。在峡谷顶部（19 m）和39 m处采样了CO_2通量。同时在峡谷的中心和壁上测量了垂直的CO_2浓度分布。除混合层高度引起的预期的一般昼夜模式外，街道峡谷中的CO_2浓度分布以及与以上各层的交换过程还显示出相对于峡谷的强风向依赖性。由于产生了像开瓶器一样的峡谷涡流，因此峡谷内CO_2的积累受到不同分布模式的调节。每日流量数据的评估为峡谷内CO_2分布的垂直和水平差异提供了很好的解释。峡谷顶部的日通量特性几乎可以完全用强线性相关性表示的交通密度来解释。甚至在39 m的通量的昼夜变化过程中，在东风条件下也显示出与交通密度显着的关系，而在西风情况下，向排放量较低的源区的变化导致通量减小。

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