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氨(NH3)是大气环境中一种重要的活性氮,对生态环境有着重要影响:NH3与气态硫酸(H2SO4)反应会生成硫酸铵((NH4)2SO4)或硫酸氢铵(NH4HSO4)气溶胶,与气态硝酸(HNO3)反应会生成硝酸铵(NH4NO3)气溶胶,这些气溶胶是大气细颗粒物(PM2.5)的重要组成成分[1]。高浓度的PM2.5是产生雾霾的主要因素,影响大气能见度及大气辐射强迫,引发一系列环境效应,对人体健康产生不利影响[2-3]。NH3通过干湿沉降进入地面或水体中,会导致土壤酸化及水体富营养化,对生态环境产生影响[4-5]。
植被冠层可作为大气NH3的源或汇,交换方向和大小受冠层内及大气中NH3浓度梯度影响[6-7],植被冠层NH3交换受到土壤、叶片表皮、叶片气孔等影响:叶片气孔与大气中NH3交换是双向的,叶片表皮则通常为NH3的汇[8-11]。近年来,对农业系统植被冠层-大气NH3交换以及冠层内NH3浓度梯度已开展了大量观测研究[12-13],且根据NH3在植被-大气中双向交换的特点和规律建立了双向交换概念模型并进行了参数化处理[8],并广泛用于农田和森林系统土壤-植被-大气NH3交换的模拟和预测[11, 14-15]。城市绿化植被作为城市的重要组成部分,被认为是主要的城市净化系统,其冠层与大气也存在NH3的交换。但目前对城市绿化植被NH3变化观测基础数据十分缺乏,城市绿化植被与大气NH3交换过程尚不明确,冠层内部NH3浓度梯度及源汇关系不清。
本研究基于典型城市绿化植被系统测量了植被冠层内部及冠层上方自由大气中NH3浓度梯度,并同步获得冠层下绿化植被质外体氨补偿点(χs),为今后进一步深入研究城市绿化植被对大气NH3的调节以及空气质量影响提供基础数据。
城市绿化林中大气氨浓度垂直分布观测
Observation on the vertical distribution of atmospheric ammonia in urban green vegetation canopy
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摘要: 城市绿化植被与大气存在氨气(NH3)交换,但冠层内部NH3源汇关系不清。本研究基于典型城市绿化植被系统测量了植被冠层内不同高度及自由大气中NH3浓度梯度,并同步获得冠层下绿化植物质外体氨补偿点(χs)。结果表明,观测期间NH3浓度日变化明显,不同高度NH3浓度均为白天高于夜间,白天、夜间NH3整体平均浓度分别为(12.5±3.35) μg·m−3 和(11.9±2.76 )μg·m−3 。冠层内NH3浓度随高度增加降低,单位高度(m)降低量与所在高度植被密度有关。对植被补偿点的观测表明植物对NH3主要起到吸收作用,与城市空旷地区NH3浓度梯度相比,植被NH3吸收作用大于NH3干沉降作用对冠层NH3浓度梯度的影响;与农作物冠层内NH3浓度梯度相比,城市较为分散的植被分布导致绿化植被冠层内气体混合相对均匀,其NH3浓度梯度相对农作物冠层差异不明显。本研究为今后进一步深入研究城市绿化植被对大气NH3的调节以及空气质量影响提供基础数据。Abstract: There is an exchange of ammonia (NH3) between urban green vegetation and atmosphere, but the relationship of source and sink of NH3 in the canopy is unclear. Based on the typical urban green vegetation system, the NH3 concentration gradients in the canopy and free atmosphere were measured, and the ammonia compensation points (χs) of vegetation on the ground were obtained at the same time. Results showed that the diurnal variation of NH3 was distinct during the observation period, and the average concentration of NH3 was (12.5±3.35 )μg·m−3 in the daytime, which was higher than those in night((11.9±2.76) μg·m−3).The concentration of NH3 in the canopy decreased with the increase of height, and the reduction of unit height (m) was related to the density of vegetation at that layer. The calculation of χs showed that NH3 was absorbed by the plants. Comparing the discrepancy of NH3 concentration gradient between vegetation covered area and the area without vegetation in urban, we found that the effect of vegetation absorption on NH3 concentration gradient was greater than NH3 dry deposition in canopy. Compared with the concentration gradient of NH3 in crop canopy, the gas mixing in-canopy of urban vegetation was more sufficient with the relatively scattered vegetation distribution, and caused the gradient of ammonia in the canopy vegetation was not obvious.
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Key words:
- urban green vegetation /
- canopy /
- ammonia /
- vertical distribution
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表 1 本研究与其他NH3垂直浓度(μg·m−3)梯度观测研究对比
Table 1. Overview of measured vertical NH3 concentrations (μg·m−3) in previous studies and in this study
空旷地(农村)
Open area (Rural)玉米
Corn甘蔗
Sugar cane空旷地(北京)
Open area (Beijing)空旷地(北京)
Open area (Beijing)绿植覆盖(北京)
Open area (Beijing)0 m — 8.8 173.3 — — 12.4 1 m 6.8(1 m) 3.1 78.3 — — 12.3 1—5 m 11.5(4 m) — 61.8(2 m) — 12.5 12.2(3 m) 5—10 m — — — 7.9 13.4 12.1 10—20 m 9.6 — — 15.8 13.8 11.7(15 m) 日期 (Data) 2014.07 2005 2017.07 2019.02 2016.03—2017.03 2019.09 参考文献 [25] [12] [13] [26] [27] 本研究 -
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