Physical and Environmental Sciences Department; Center for Water Supply Studies, Texas A&M University, Corpus Christi, USA.
Physical and Environmental Sciences Department; Center for Water Supply Studies, Texas A&M University, Corpus Christi, USA.
Environ Pollut. 2023 Jan 1;316(Pt 1):120537. doi: 10.1016/j.envpol.2022.120537. Epub 2022 Nov 1.
Urban ammonia (NH) emissions contribute to poor local air quality and can be transported to rural landscapes, impacting sensitive ecosystems. The Colorado Front Range urban corridor encompasses the Denver Metropolitan Area, rural farmland/rangeland and montane forest between the city and the Rocky Mountains. Reactive nitrogen emissions from the corridor are partly responsible for increased N deposition to the wildland-urban interface (WUI) in this region. To determine the significance of individual NH sources to WUI ecosystems, we measured the concentration and isotopic composition (δN-NH) of ambient NH from April to October 2018 across a five-site urban to rural gradient in the corridor. The urban sites had higher NH concentrations and δN-NH values than the rural/suburban sites. Based on isotope mixing models, NH emission source contributions for all sites were fertilizer (12 ± 5.7%), livestock waste (18 ± 12%), vehicles (37 ± 23%), and biomass burning (34 ± 20%). Vehicle contributions were consistent across all months with an average of 35% and summer months showed a peak in biomass burning contributions (40%). As wildfires are projected to increase due to climate change, we stress a need for constraints on the isotopic signature of NH emitted from wildfires. Vehicle emissions contributed the greatest amount of NH (40%) at the urban sites while rural/suburban sites had higher agricultural contributions (41%). Had 2018 not had an anomalously high wildfire season, 46% and 60% of the NH would have been attributed to vehicle emissions at the WUI site and urban sites, respectively. NH emissions have historically been ascribed to agricultural activities but these findings illustrate the universal significance of vehicle emissions and the potential for sustained wildfire activity to be a primary contributor to NH. Air quality (e.g., particulate matter) and nitrogen deposition reduction plans may benefit by including management practices that address vehicle NH emissions.
城市氨气（NH）排放会导致当地空气质量变差，并可能被输送到农村地区，对敏感生态系统造成影响。科罗拉多落矶山山前带城市走廊包括丹佛大都市区、城市和落矶山脉之间的农村农田/牧场和山地森林。该走廊的活性氮排放部分导致了该地区野生-城市交错带（WUI）的氮沉积增加。为了确定个别 NH 源对 WUI 生态系统的重要性，我们在走廊的五个城市到农村梯度站点测量了 2018 年 4 月至 10 月的环境 NH 浓度和同位素组成（δN-NH）。城市站点的 NH 浓度和 δN-NH 值高于农村/郊区站点。基于同位素混合模型，所有站点的 NH 排放源贡献分别为肥料（12 ± 5.7%）、牲畜废物（18 ± 12%）、车辆（37 ± 23%）和生物质燃烧（34 ± 20%）。在所有月份，车辆的贡献都是一致的，平均为 35%，夏季生物质燃烧的贡献达到峰值（40%）。由于气候变化预计会增加野火，我们强调需要限制野火排放的 NH 同位素特征。在城市站点，车辆排放的 NH 量最大（40%），而农村/郊区站点的农业贡献较高（41%）。如果 2018 年没有异常高的野火季节，WUI 站点和城市站点的 NH 将分别有 46%和 60%归因于车辆排放。NH 排放历史上归因于农业活动，但这些发现说明了车辆排放的普遍重要性，以及持续的野火活动可能成为 NH 的主要贡献源。空气质量（例如颗粒物）和氮沉积减少计划可能受益于包括解决车辆 NH 排放的管理措施。
