Abstract：
Aerosol ammonium (NH4+), mainly produced from the reactions of ammonia (NH3) with acids in the atmosphere, has significant impacts on air pollution, radiative forcing, and human health. Understanding the source and formation mechanism of NH4+ can provide scientific insights into air quality improvements. However, the sources of NH3 in urban areas are not well understood, and few studies focus on NH3/NH4+ at different heights within the atmospheric boundary layer, which hinders a comprehensive understanding of aerosol NH4+. In this study, we perform both field observation and modeling studies (the Community Multiscale Air Quality, CMAQ) to investigate regional NH3 emission sources and vertically resolved NH4+ formation mechanisms during the winter in Beijing. Both stable nitrogen isotope analyses and CMAQ model suggest that combustion-related NH3 emissions, including fossil fuel sources, NH3 slip, and biomass burning, are important sources of aerosol NH4+ with more than 60% contribution occurring on heavily polluted days. In contrast, volatilization-related NH3 sources (livestock breeding, N-fertilizer application, and human waste) are dominant on clean days. Combustion-related NH3 is mostly local from Beijing, and biomass burning is likely an important NH3 source (∼15%-20%) that was previously overlooked. More effective control strategies such as the two-product (e.g., reducing both SO2 and NH3) control policy should be considered to improve air quality.
摘要：
气溶胶铵（NH4+），主要由氨（NH3）与大气中的酸反应产生，对空气污染有重大影响，辐射强迫，和人类健康。了解NH4+的来源和形成机制可以为空气质量改善提供科学见解。然而,城市地区的NH3来源还不清楚，很少有研究关注大气边界层内不同高度的NH3/NH4+，这阻碍了对气溶胶NH4+的全面了解。在这项研究中,我们进行现场观察和建模研究(社区多尺度空气质量，CMAQ）调查了北京冬季区域NH3排放源和垂直解析的NH4形成机制。稳定的氮同位素分析和CMAQ模型都表明与燃烧相关的NH3排放，包括化石燃料来源，NH3泄漏,生物质燃烧，是气溶胶NH4的重要来源，在严重污染的日子里有超过60％的贡献。相比之下,与挥发相关的NH3源(家畜育种，氮肥施用,和人类废物)在清洁的日子里占主导地位。与燃烧有关的NH3主要来自北京，生物质燃烧可能是以前被忽视的重要NH3源(~15%-20%)。更有效的控制策略，如双产品(例如，应考虑减少SO2和NH3）控制政策，以改善空气质量。
