Abstract:

Ammonia (NH₃) and amines, which are key alkaline gases, play pivotal roles in atmospheric nitrogen cycling, air quality, and human health. Although gasoline vehicles are a significant source of NH₃ and amine emissions, their emission profiles have not been inadequately characterized. This study addresses this gap by conducting on-road measurements of NH₃ and amines in particulate matter (PM) emitted from nine light-duty gasoline trucks adhering to different emission standards (China V and China VI). The findings revealed that the emission factors for NH₃ and amines in PM from gasoline vehicle exhaust were (1479.3±1745.7) μg·kg⁻¹ and (701.1±169.5) ng·kg⁻¹, respectively. Notably, the NH₃ concentrations in PM were 3-4 orders of magnitude higher than those of amines, underscoring the critical need for a heightened focus on NH₃ emissions from gasoline vehicles. Furthermore, the emission factors for NH₃ in PM from China V and China VI standard vehicles were (2208.8±2169.9) μg·kg⁻¹ and (822.8±801.8) μg·kg⁻¹, respectively. Similarly, the amine emission factors in PM from China V standard vehicles [(1341.7±2931.0) ng·kg⁻¹] were significantly higher than those from China VI standard vehicles [(530.5±199.1) ng·kg⁻¹]. These results demonstrate that stricter emission standards effectively curtail NH₃ and amine emissions in PM, primarily due to enhanced PM emission control in the China VI standards, which substantially reduces PM concentration per unit mass of fuel combustion, thereby indirectly lowering emissions of nitrogen-containing compounds, such as NH₃ and amines. Additionally, the emission factors of NH₃ and amines from both the China V and China VI standard gasoline vehicles exhibited an initial decreasing trend, followed by an increase with vehicle speed. Specifically, the emission factors decreased with increasing speed in the low- to medium-speed range (0-60 km·h⁻¹), but increased in the medium- to high-speed range (60-90 km·h⁻¹), reaching their lowest levels under medium-speed conditions. For instance, NH₃ emission factors in PM from China V standard vehicles under low-, medium-, and high-speed conditions were (2581.4±1708.5) μg·kg⁻¹, (1352.0±883.5) μg·kg⁻¹, and (2692.9± 3052.5) μg·kg⁻¹, respectively. NH₃ emissions under low-speed conditions were 1.9 and 0.96 times those under medium- and high-speed conditions, respectively, indicating the lowest NH₃ emissions under medium-speed conditions. Similarly, the China VI standard vehicles exhibited the lowest NH₃ emissions under medium speed conditions. The amine emission factors under high-speed conditions were 2.2 and 19.6 times those under low- and medium-speed conditions, respectively, further confirming the lowest emissions under medium-speed conditions. This phenomenon is attributed to the optimal air-fuel ratio and exhaust temperature under medium-speed conditions, which enhanced the synergistic removal efficiency of NH₃ and amines by the three-way catalytic converter (TWC). Among the amine components, C2−amines (e.g., DMAH⁺ and EAH⁺) were the dominant species across the different emission standards and driving speeds, accounting for 71.8%-96.1% of the total amines. This study employed both the control variable method and random forest model to quantitatively assess the relative contributions of emission standards and driving speed to NH₃ and amine emissions. The results indicated that emission standards were the primary factors influencing NH₃ and amine emissions compared with driving speed. For instance, compared with China V standard vehicles, China VI standard vehicles reduced NH₃ and organic amine emissions in PM by 62.7% and 60.5%, respectively. Specifically, MMAH⁺, DMAH⁺, EAH⁺, TMAH⁺, DEAH⁺, and TEAH⁺ emissions decreased by 95.3%, 82.0%, 37.5%, 98.8%, 93.0%, and 94.0%, respectively, with the implementation of stricter emission standards. This suggests that upgrading gasoline vehicle emission standards can significantly reduce the NH₃ and amine emissions from PM. This study provides novel insights into the emission characteristics of NH₃ and amines from gasoline vehicles, offering valuable information for formulating stricter emission control policies and optimizing the post-treatment technologies. However, owing to limitations in data availability, this study did not comprehensively cover all potential influencing factors of the study variables. Future research should expand the sample size and incorporate additional factors, such as driving mileage and engine displacement, while combining laboratory simulations with real-world driving tests to deepen the understanding of NH₃ and amine emission mechanisms in gasoline vehicle exhausts. This study contributes to a better understanding of the NH₃ and amine emission profiles of gasoline vehicles, providing a scientific basis for improving air quality and guiding future emission control strategies.

Key words: gasoline vehicles, NH₃ and amines, emission characteristics, random forest model, influence factors

摘要：

氨和有机胺作为为数不多的碱性气体，可显著影响大气氮循环、环境空气质量和人体健康。汽油车作为氨和有机胺的重要排放源，其排放特征尚不清楚。基于车载实验对9辆不同排放标准轻型汽油卡车尾气颗粒物中氨和有机胺的排放开展实测。结果发现，汽油车尾气颗粒物中氨的排放量[(1479.3±1745.7) μg·kg⁻¹]显著高于有机胺[(701.1±169.5) ng·kg⁻¹]，两者相差3-4个数量级，且两者在颗粒相的分布特征会受环境温湿度的影响。其次，汽油车排放标准的提高可以显著抑制颗粒物中氨和有机胺的排放，如国五标准汽油车颗粒物中有机胺的排放因子[(1341.7±199.1) ng·kg⁻¹]显著高于国六[(530.5±1597.1) ng·kg⁻¹]。再者，随着行驶速度的增加汽油车颗粒物中氨和有机胺的排放因子呈现出先减小再增大的趋势，表现为中速条件下排放最低。不同排放标准和行驶速度的汽油车中C2−胺（如DMAH⁺和EAH⁺）是有机胺的绝对优势组分，占比可达71.8%-96.1%。此外，结合控制变量法和随机森林模型分析发现汽油车排放标准是影响氨和有机胺排放的主要控制因子，提高排放标准可以显著降低汽油车颗粒物中氨和有机胺的排放。这项工作为掌握汽油车颗粒物中氨和有机胺的排放特征提供了新的认识，可有效服务于空气质量的改善。

关键词: 汽油车, 氨和有机胺, 排放特征, 随机森林模型, 影响因素