Department of Applied Physics, Faculty of Sciences, University of Valladolid, Paseo de Belén, 7, 47011 Valladolid, Spain.
Department of Applied Physics, Faculty of Sciences, University of Valladolid, Paseo de Belén, 7, 47011 Valladolid, Spain.
Sci Total Environ. 2014 Apr 1;476-477:158-64. doi: 10.1016/j.scitotenv.2014.01.019. Epub 2014 Jan 23.
This paper provides evidence that symmetry of CO2 concentration distribution may indicate sources or dispersive processes. Skewness was calculated by different procedures with CO2 measured at a rural site using a Picarro G1301 analyser over a two-year period. The usual skewness coefficient was considered together with fourteen robust estimators. A noticeable contrast was obtained between day and night, and skewness decreased linearly with the logarithm of the height. One coefficient was selected from its satisfactory relationship with the median concentration in daily evolution. Three analyses based on the kernel smoothing method were conducted with this coefficient to investigate its response to yearly and daily evolutions, wind direction, and wind speed. Left-skewed distributions were linked to thermal turbulence during midday, especially in spring-summer, or with high wind speeds. Almost symmetric distributions were associated with sources, such as the Valladolid City plume reinforced with spring emissions and the lack of emissions in summer in the remaining directions. Finally, right-skewed distributions were related to low wind speeds and stable stratification at night, furthered by strong emissions in spring. Skewness intervals were proposed and their average median concentrations were calculated such that the relationship between skewness and concentration depends on the analysis performed. Since some skewness coefficients may also be negative, they provide better information about sources or dispersive processes than concentration.
本文提供了证据表明 CO2 浓度分布的对称性可能表明源或扩散过程。在两年的时间里，使用 Picarro G1301 分析仪在农村站点测量 CO2，通过不同的程序计算偏度。考虑了通常的偏度系数和 14 个稳健估计量。白天和黑夜之间存在明显的对比，偏度随高度的对数线性减小。从与每日浓度变化的中位数的良好关系中选择了一个系数。使用该系数进行了基于核平滑方法的三种分析，以研究其对年变化、日变化、风向和风速的响应。在中午，与热湍流有关的偏态分布，尤其是在春夏季节，或者与高风速有关的偏态分布。几乎对称的分布与源有关，例如在春季排放增强的巴利亚多利德城市羽流，以及在其他方向夏季缺乏排放。最后，与夜间低风速和稳定分层有关的偏态分布，在春季强排放的作用下进一步加剧。提出了偏度区间，并计算了它们的平均中位数浓度，使得偏度和浓度之间的关系取决于所进行的分析。由于一些偏度系数也可能为负，因此它们比浓度更能提供有关源或扩散过程的信息。
