A top-down approach of surface carbonyl sulfide exchange by a Mediterranean oak forest ecosystem in southern France
A top-down approach of surface carbonyl sulfide exchange by a Mediterranean oak forest ecosystem in southern France
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DOI：
10.5194/acp-16-14909-2016
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发表时间：
2016-12-02
影响因子：
6.3
通讯作者：
Genty, Bernard
中科院分区：
文献类型：
--
作者：
Belviso, Sauveur;Reiter, Ilja Marco;Genty, Bernard
在法国南部的地中海森林生态系统中，土壤，树叶和大气动力学对表面羰基硫（OCS）交换的作用（O3 HP）在2012年6月和2013年6月进行了调查，基本上是一种自上而下的方法。大气数据表明，该网站是适当的估计总初级生产力（GPP）直接从涡度协方差测量的OCS通量，但它是不够的缩放净生态系统交换（NEE）GPP从观测的垂直梯度OCS相对于CO2在白天。首先，OCS和二氧化碳（CO2）的日变化和垂直梯度显示没有净交换OCS在夜间时，生态系统呼吸的碳通量占主导地位。这与其他橡树林地生态系统的地中海气候，在夜间吸收OCS的土壤和/或植被已经观察到。由于温度，水，和有机碳含量的土壤中的O3 HP应有利于OCS的吸收，夜间净吸收的缺乏将表明，其在土壤中的总消耗是由排放过程，仍然是其特征的补偿。其次，在光合作用期间OCS的吸收以两种不同的方式表征。我们测量了臭氧（O-3）的沉积速度和估计的分区O-3沉积之间的气孔和非气孔途径开始前的OCS和O-3表面浓度的联合调查。我们观察到的气孔通路的相对重要性在上午的时间和同步急剧下降的OCS（幅度在60-100 ppt的范围内）和O-3（幅度在15-30 ppb的范围内）的混合比日出后，在夜间边界层的破裂。植物对OCS的吸收也从垂直剖面进行了表征。然而，在2012年6月，计算生态系统对外大陆架的相对吸收（ERU）的时间窗口被限制在中午之后的几个小时内，而外大陆架是划分所测量的NEE的有用工具。这是由于OCS的垂直分布的中断夹带OCS丰富的对流层空气在早上，因为垂直梯度的CO2反转时，它仍然是轻的。此外，2013年6月白天，受污染的空气质量（高达700 ppt的OCS）导致大气OCS/CO2比率发生巨大变化，进一步减少了ERU计算的时间窗口。
The role that soil, foliage, and atmospheric dynamics have on surface carbonyl sulfide (OCS) exchange in a Mediterranean forest ecosystem in southern France (the Oak Observatory at the Observatoire de Haute Provence, O3HP) was investigated in June of 2012 and 2013 with essentially a top-down approach. Atmospheric data suggest that the site is appropriate for estimating gross primary production (GPP) directly from eddy covariance measurements of OCS fluxes, but it is less adequate for scaling net ecosystem exchange (NEE) to GPP from observations of vertical gradients of OCS relative to CO2 during the daytime. Firstly, OCS and carbon dioxide (CO2) diurnal variations and vertical gradients show no net exchange of OCS at night when the carbon fluxes are dominated by ecosystem respiration. This contrasts with other oak woodland ecosystems of a Mediterranean climate, where nocturnal uptake of OCS by soil and/or vegetation has been observed. Since temperature, water, and organic carbon content of soil at the O3HP should favor the uptake of OCS, the lack of nocturnal net uptake would indicate that its gross consumption in soil is compensated for by emission processes that remain to be characterized. Secondly, the uptake of OCS during the photosynthetic period was characterized in two different ways. We measured ozone (O-3) deposition velocities and estimated the partitioning of O-3 deposition between stomatal and non-stomatal pathways before the start of a joint survey of OCS and O-3 surface concentrations. We observed an increasing trend in the relative importance of the stomatal pathway during the morning hours and synchronous steep drops of mixing ratios of OCS (amplitude in the range of 60-100 ppt) and O-3 (amplitude in the range of 15-30 ppb) after sunrise and before the break up of the nocturnal boundary layer. The uptake of OCS by plants was also characterized from vertical profiles. However, the time window for calculation of the ecosystem relative uptake (ERU) of OCS, which is a useful tool for partitioning measured NEE, was limited in June 2012 to a few hours after midday. This was due to the disruption of the vertical distribution of OCS by entrainment of OCS rich tropospheric air in the morning and because the vertical gradient of CO2 reverses when it is still light. Moreover, polluted air masses (up to 700 ppt of OCS) produced dramatic variation in atmospheric OCS/CO2 ratios during the daytime in June 2013, further reducing the time window for ERU calculation.