Gas-phase ammonia (NH₃), emitted primarily from agriculture, contributes significantly to reactive nitrogen (N_r) deposition. Excess deposition of N_r to the environment causes acidification, eutrophication, and loss of biodiversity. The exchange of NH₃ between land and atmosphere is bidirectional and can be highly heterogenous when underlying vegetation and soil characteristics differ. Direct measurements that assess the spatial heterogeneity of NH₃ fluxes are lacking. To this end, we developed and deployed two fast-response, quantum cascade laser-based open-path NH₃ sensors to quantify NH₃ fluxes at a deciduous forest and an adjacent grassland separated by 700 m in North Carolina, United States from August to November, 2017. The sensors achieved 10 Hz precisions of 0.17 ppbv and 0.23 ppbv in the field, respectively. Eddy covariance calculations showed net deposition of NH₃ (-7.3 ng NH₃-N m⁻² s⁻¹) to the forest canopy and emission (3.2 ng NH₃-N m⁻² s⁻¹) from the grassland. NH₃ fluxes at both locations displayed diurnal patterns with absolute magnitudes largest midday and with smaller peaks in the afternoons. Concurrent biogeochemistry data showed over an order of magnitude higher NH₃ emission potentials from green vegetation at the grassland compared to the forest, suggesting a possible explanation for the observed flux differences. Back trajectories originating from the site identified the upwind urban area as the main source region of NH₃. Our work highlights the fact that adjacent natural ecosystems sharing the same airshed but different vegetation and biogeochemical conditions may differ remarkably in NH₃ exchange. Such heterogeneities should be considered when upscaling point measurements, downscaling modeled fluxes, and evaluating N_r deposition for different natural land use types in the same landscape. Additional in-situ flux measurements accompanied by comprehensive biogeochemical and micrometeorological records over longer periods are needed to fully characterize the temporal variabilities and trends of NH₃ fluxes and identify the underlying driving factors.

主要从农业排放的气相氨 (NH ₃ ) 对活性氮 (N _r ) 沉积有重要贡献。_{N r}过量沉积到环境中会导致酸化、富营养化和生物多样性丧失。_{陆地和大气之间的 NH 3}交换是双向的，并且当底层植被和土壤特征不同时可能是高度异质的。缺乏评估NH ₃通量的空间异质性的直接测量。为此，我们开发并部署了两个快速响应、基于量子级联激光的开路 NH ₃传感器来量化 NH ₃2017 年 8 月至 11 月，美国北卡罗来纳州的落叶林和相距 700 m 的相邻草地的通量。传感器在现场分别实现了 0.17 ppbv 和 0.23 ppbv 的 10 Hz 精度。涡流协方差计算显示 NH ₃ (-7.3 ng NH ₃ -N m ^-2 s ^-1 ) 向森林冠层的净沉积和草地的排放 (3.2 ng NH ₃ -N m ^-2 s ^-1 )。两个位置的NH ₃通量均显示出日变化，中午绝对量级最大，下午峰值较小。_{同期生物地球化学数据显示，NH 3}高出一个数量级以上与森林相比，草地上绿色植被的排放潜力，这为观察到的通量差异提供了可能的解释。来自该场地的回溯轨迹确定上风城区是NH ₃的主要来源区。_{我们的工作强调了这样一个事实，即相邻的自然生态系统共享相同的空气流域但不同的植被和生物地球化学条件在 NH 3}交换中可能存在显着差异。_{在放大点测量、缩小模拟通量和评估 N r}时，应考虑这种异质性同一景观中不同自然土地利用类型的沉积。需要额外的原位通量测量以及更长时间的综合生物地球化学和微气象记录，以充分表征 NH ₃通量的时间变化和趋势，并确定潜在的驱动因素。