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

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。

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 ofχs 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.