Over the past several years, it has become apparent that vehicular emissions include significant quantities of ammonia (NH₃) arising from the implementation of increasingly stringent nitrogen oxide (NOx) emissions controls on light-duty (LDV) and heavy-duty (HDV) vehicles. (1) In the case of LDVs, the NH₃ forms and slips through the catalytic reduction of NOx in the 3-way catalyst systems and the selective catalytic reduction (SCR), although details of the mechanism are not fully understood. Using remote sensing methods, Farren et al. (2) reported that NH₃ emissions increased as vehicle mileage increased and that cold start emissions were 1.7 times higher than when the catalyst was fully operational. Emissions from HDVs and new diesel LDVs come from overdosing with urea and maldistribution of the NH₃ decomposed from the urea on the catalyst during SCR. (3) As a result of these increased NOx controls, vehicular emissions might now be the dominant urban source of NH₃ (see Zhou et al. and references therein as an example). (4) A recent study by Reche et al. (5) has also found that NH₃ concentrations were highest at the traffic site in Barcelona compared to a number of other locations. They also found that concentrations have been increasing over the past decade (2011–2020). At this time, we do not know why the concentrations are increasing. Are the changing control technologies, such as moving from Euro 2 to Euro 6d or Tier 2 to Tier 3 vehicles, resulting in increased emissions per vehicle? Farren et al. (2) reported decreased NH₃ emissions from Euro 2 (1.13 ± 0.04 g/kg) to Euro 6 (0.49 ± 0.01 g/kg) for gasoline and gasoline-hybrid vehicles, so it appears that better controls on spark-ignition passenger cars are not increasing the per vehicle emissions. However, similar information is not available for U.S. vehicles as they move from Tier 2 to Tier 3 standards, and there are no data on the LDV diesel Euro6 and especially Euro6d that are equipped with SCR systems using urea. In the United States, SCRs in HDVs started being sold in 2010 and have been increasing in the fleet over the past decade. Measurements of 277 U.S. HDVs found that SCR systems increased NH₃ emissions from near-zero levels to 0.18 ± 0.07 g/kg^–1 of fuel, respectively. The distribution of emissions of NH₃ are skewed with 10% of trucks contributing 95% of the on-road fleet’s total NH₃ emissions. Thus, both LDVs and HDVs are increasing the urban emissions of NH₃ and are contributing to local concentrations in heavily trafficked urban areas. In Europe, the Euro 6d requirements began in 2019 and required emissions measurements with methods that represented real-world emissions. However, ammonia emissions have not been reported. Those diesel cars are equipped with SCR systems using urea, and NH₃ slip might occur. Thus, the high proportion of diesel LDVs in the EU mean these emissions from SCR-equipped LDVs might be quite relevant for EU air quality but not for the US since the proportion of diesel LDVs in the US is very small. Given the importance of NH₃ in controlling the formation of particulate nitrate (NH₄NO₃) (6) and ammonium chloride (NH₄Cl) in areas where high chlorine (Cl) containing coal is burned, (7) it is important that a much greater effort be made to understand the changing NH₃ emissions from vehicles. Ammonia emissions can be reduced if manufacturers explicitly work to avoid an excessively rich gasoline/air mixture in spark ignition vehicles or excessive use of urea in the SCRs of diesel vehicles. Thus, if NH₃ were made a regulated emission species, then such efforts will be made to meet the standards, measurements will be made to ensure compliance, and the NH₃ impacts on urban PM_2.5 will be reduced as we strive to approach the new WHO air quality guidelines for PM_2.5. In the longer term, it can be expected that we will replace combustion-based transport with electric vehicles (EVs) and NOx and NH₃ emissions will cease to be an issue. However, even then, we have to recognize that EVs are not “zero emission” vehicles (8) and that air quality plans require additional short and midterm actions to further abate PM. Dr. Philip K. Hopke is the Bayard D. Clarkson Distinguished Professor Emeritus at Clarkson University and Adjunct Professor in the Department of Public Health Sciences of the University of Rochester School of Medicine and Dentistry. He was the founding Director of the Center for Air Resources Engineering and Science (CARES), and the Director of the Institute for a Sustainable Environment (ISE). He served as Chair of EPA’s Clean Air Scientific Advisory Committee (CASAC), President of the American Association for Aerosol Research (AAAR), and was a member of the multiple advisory committees. He is a fellow of the International Aerosol Research Assembly, the American Association for the Advancement of Science, the Air and Waste Management Association, and the AAAR. His research interests include chemical characterization of ambient aerosol samples, multivariate statistical methods for data analysis, characterization of source/receptor relationships for ambient air pollutants, indoor air quality, and exposure and risk assessment. This article references 8 other publications. This article has not yet been cited by other publications. Dr. Philip K. Hopke is the Bayard D. Clarkson Distinguished Professor Emeritus at Clarkson University and Adjunct Professor in the Department of Public Health Sciences of the University of Rochester School of Medicine and Dentistry. He was the founding Director of the Center for Air Resources Engineering and Science (CARES), and the Director of the Institute for a Sustainable Environment (ISE). He served as Chair of EPA’s Clean Air Scientific Advisory Committee (CASAC), President of the American Association for Aerosol Research (AAAR), and was a member of the multiple advisory committees. He is a fellow of the International Aerosol Research Assembly, the American Association for the Advancement of Science, the Air and Waste Management Association, and the AAAR. His research interests include chemical characterization of ambient aerosol samples, multivariate statistical methods for data analysis, characterization of source/receptor relationships for ambient air pollutants, indoor air quality, and exposure and risk assessment. This article references 8 other publications.

中文翻译：

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改进的车辆 NOx 控制是否会导致城市 NH3 排放量增加？

在过去几年中，由于对轻型 (LDV) 和重型 (HDV) 实施日益严格的氮氧化物 (NOx) 排放控制，车辆排放包括大量氨 (NH ₃ ) 已变得很明显车辆。(1) 在 LDV 的情况下，NH ₃在三元催化系统中的 NOx 催化还原和选择性催化还原 (SCR) 中形成并逸出，尽管其机理的细节尚不完全清楚。Farren 等人使用遥感方法。(2)报道NH ₃排放量随着车辆行驶里程的增加而增加，冷启动排放量是催化剂完全运行时的 1.7 倍。HDV 和新型柴油 LDV 的排放来自过量使用尿素和在 SCR 期间从尿素分解的 NH _{3在催化剂上的分布不均。}(3) 由于这些增加的 NOx 控制，车辆排放现在可能是 NH ₃的主要城市来源（参见 Zhou 等人及其参考文献作为示例）。(4) Reche 等人最近的一项研究。(5) 还发现NH ₃与其他一些地点相比，巴塞罗那交通站点的浓度最高。他们还发现，过去十年（2011-2020）的浓度一直在增加。目前，我们不知道为什么浓度会增加。不断变化的控制技术，例如从 Euro 2 到 Euro 6d 或从 Tier 2 到 Tier 3 的车辆，是否会导致每辆车的排放量增加？法伦等人。(2) 报告减少NH ₃汽油和汽油混合动力汽车的排放量从欧 2 (1.13 ± 0.04 g/kg) 到欧 6 (0.49 ± 0.01 g/kg)，因此对火花点火乘用车的更好控制似乎并没有增加每辆车的排放量. 但是，由于美国车辆从 Tier 2 转向 Tier 3 标准，因此没有类似的信息，并且没有关于配备使用尿素的 SCR 系统的 LDV 柴油 Euro6 尤其是 Euro6d 的数据。在美国，HDV 中的 SCR 于 2010 年开始销售，并且在过去十年中一直在增加。对 277 辆美国 HDV 的测量发现，SCR 系统分别将 NH ₃排放量从接近零的水平增加到 0.18 ± 0.07 g/kg ^–1燃料。NH _{3排放分布}10% 的卡车占公路车队总 NH ₃排放量的 95%。因此，LDV 和 HDV 都在增加城市 NH ₃的排放，并导致交通繁忙的城市地区局部浓度增加。在欧洲，欧 6d 要求始于 2019 年，要求使用代表实际排放的方法进行排放测量。然而，尚未报告氨排放。这些柴油车配备了使用尿素的 SCR 系统，可能会发生 NH ₃泄漏。因此，欧盟柴油 LDV 的高比例意味着配备 SCR 的 LDV 的这些排放可能与欧盟空气质量非常相关，但与美国无关，因为美国柴油 LDV 的比例非常小。鉴于 NH 的重要性₃在燃烧含高氯 (Cl) 的煤的地区控制颗粒硝酸盐 (NH ₄ NO ₃ ) (6) 和氯化铵 (NH ₄ Cl) 的形成，(7) 重要的是要付出更大的努力了解车辆的 NH ₃排放变化。如果制造商明确努力避免火花点火车辆中的汽油/空气混合物过浓或柴油车辆的 SCR 中过度使用尿素，则可以减少氨排放。因此，如果将 NH ₃设为管制排放物种，则将努力达到标准，将进行测量以确保合规性，以及 NH ₃对城市 PM _{2.5的影响随着我们努力接近世界卫生组织新的 PM 2.5}空气质量指南，将会减少。从长远来看，可以预期我们将用电动汽车 (EV) 以及 NOx 和 NH _{3取代基于燃烧的交通工具}排放将不再是一个问题。然而，即便如此，我们也必须认识到电动汽车不是“零排放”车辆 (8)，空气质量计划需要额外的短期和中期行动来进一步减少 PM。Philip K. Hopke 博士是克拉克森大学的 Bayard D. Clarkson 杰出名誉教授和罗切斯特大学医学和牙科学院公共卫生科学系的兼职教授。他是空气资源工程与科学中心 (CARES) 的创始主任和可持续环境研究所 (ISE) 的主任。他曾担任 EPA 清洁空气科学咨询委员会 (CASAC) 主席、美国气溶胶研究协会 (AAAR) 主席，并且是多个咨询委员会的成员。他是国际气溶胶研究大会、美国科学促进会、空气和废物管理协会以及 AAAR 的成员。他的研究兴趣包括环境气溶胶样品的化学表征、数据分析的多元统计方法、环境空气污染物的源/受体关系表征、室内空气质量以及暴露和风险评估。本文引用了其他 8 个出版物。这篇文章尚未被其他出版物引用。Philip K. Hopke 博士是克拉克森大学的 Bayard D. Clarkson 杰出名誉教授和罗切斯特大学医学和牙科学院公共卫生科学系的兼职教授。他是空气资源工程与科学中心 (CARES) 的创始主任和可持续环境研究所 (ISE) 的主任。他曾担任 EPA 清洁空气科学咨询委员会 (CASAC) 主席、美国气溶胶研究协会 (AAAR) 主席，并且是多个咨询委员会的成员。他是国际气溶胶研究大会、美国科学促进会、空气和废物管理协会以及 AAAR 的成员。他的研究兴趣包括环境气溶胶样品的化学表征、数据分析的多元统计方法、环境空气污染物的源/受体关系表征、室内空气质量以及暴露和风险评估。本文引用了其他 8 个出版物。