• 关键词：氨气  质子转移反应质谱  正交矩阵因子分解法(PMF)  农业源  北方平原

• 基金项目：国家重点研发计划（No.2017YFC0209501）；大气污染防治攻关项目（No.DQGG0103-02）；国家自然科学基金（No.41675126，41730106）

• 史林林
• 1. 南京信息工程大学环境科学与工程学院, 南京 210044;2. 江苏省大气环境监测与污染控制高技术研究重点实验室, 南京 210044

• 房鑫
• 北京大学环境科学与工程学院, 环境模拟与污染控制国家重点联合实验室, 北京 100871

• 杨栋森
• 1. 南京信息工程大学环境科学与工程学院, 南京 210044;2. 江苏省大气环境监测与污染控制高技术研究重点实验室, 南京 210044

• 郭松
• 北京大学环境科学与工程学院, 环境模拟与污染控制国家重点联合实验室, 北京 100871

• 郑军
• 1. 南京信息工程大学环境科学与工程学院, 南京 210044;2. 江苏省大气环境监测与污染控制高技术研究重点实验室, 南京 210044

• 马嫣
• 1. 南京信息工程大学环境科学与工程学院, 南京 210044;2. 江苏省大气环境监测与污染控制高技术研究重点实验室, 南京 210044

• 马鑫
• 1. 南京信息工程大学环境科学与工程学院, 南京 210044;2. 江苏省大气环境监测与污染控制高技术研究重点实验室, 南京 210044

• 摘要：氨是大气中广泛存在的碱性气体，已有的研究表明，氨能够参与包括硫酸/水体系的三元成核过程，进而促进新粒子的形成；同时，氨也是大气二次有机气溶胶（SOA）的重要前体物，对二次有机气溶胶的形成具有不可忽视的影响.了解大气中氨的污染情况，实现对大气中氨的高时间分辨率的在线观测，对于研究大气中氨的时空分布及来源解析，进而加深对气溶胶生成机理及气溶胶在大气辐射平衡与气候变化中作用的认识有重要意义.本研究使用一台自主搭建的质子转移反应质谱仪（PTR-MS），以丙酮作为反应试剂，由电晕放电离子源产生质子化的丙酮反应试剂离子（（C₃H₆O）_nH⁺）（n=1，2），与大气中的气态氨及其他碱性气体发生质子转移反应后进行质谱检测.丙酮（C₃H₆O）相较于水（H₂O）和乙醇（C₂H₅OH），具有更高的质子亲和力（PA=194.1 kcal·mol^-1），对PA较高的碱基化合物的选择性更好，可减少其他物质对四极杆质谱检测结果的影响.本研究在2017年11月9日—2018年1月10日和2018年11月12日—2019年1月2日华北地区气溶胶生成机理综合研究联合外场观测期间，将PTR-MS部署于山东省德州市平原县气象局观测场内，对大气中的氨气进行实时在线观测.结果表明，两次观测的气态氨平均值分别为（5.89±5.27）ppbv和（2.65±2.41）ppbv，均呈现出一个明显的日变化规律，即上午6：00—7：00出现峰值，随后逐渐下降，在下午大约15：00浓度达到最低值，随后上升.结合正交矩阵因子分解法（Positive Matrix Factorization，PMF）模型对当地近地面大气中氨气进行初步的来源分析，发现当地大气中氨气的来源主要是周边农村在冬季大量使用生物质燃料燃烧取暖造成的生活排放和当地交通源排放.两次冬季观测中当地农村取暖等生活排放分别占到66.0%和55.0%；交通排放在两次观测中分别占到27.0%和36.8%；农田土壤释放、畜牧养殖排放和工业排放等其他来源占比较低，分别是6.2%和7.5%；外部传输来源只占到很少一部分，分别是0.8%和0.7%.2018年的冬季观测相较于2017年，氨气浓度总体出现下降，主要来源还是以当地农村冬季生活和取暖燃烧排放为主，但通过相关政策管控，这一污染来源得到改善.

• Abstract：Ammonia (NH₃) is a ubiquitous basic gas in the atmosphere. Previous studies have demonstrated that ammonia can participate in ternary nucleation process including sulfuric acid and water and thus promote new particle formation (NPF) in the atmosphere. NH₃ is also an important precursor for secondary aerosol and may exert nonnegligible effects on secondary organic aerosol (SOA) formation. Hence, comprehensive understanding of the atmospheric NH₃ and obtaining high time-resolution NH₃ data sets in real time are crucial for elucidating its temporal and spatial distribution and potential sources, which are prerequisite to study the NPF mechanisms and the effects of aerosol on solar-terrestrial radiation budget and climate change. In this study, a custom-built proton-transfer reaction mass spectrometer (PTR-MS) was used to detect NH₃. The PTR-MS was equipped with a corona discharge ion source and acetone was utilized to generate reagent ions ((C₃H₆O)_nH⁺), where n can be 1 or 2. Since the proton affinity of acetone (PA=194.1 kcal·mol^-1) is much higher than that water or ethanol and the PA of most alkaline gases is higher than 200 kcal·mol^-1, most common VOCs will not be detected by acetone and therefore cannot interfere with the quadrupole mass spectrometer detection. In this study, we conducted two field measurements of NH₃ in the Northern China Plain from 9 November 2017 to 10 January 2018 and from 12 November 2018 to 2 January 2019. The observation site was located at the Meteorological Bureau of Pingyuan County of Dezhou, Shandong. During the two field campaigns, the average NH₃ were (5.89±5.27) ppbv and (2.65±2.41) ppbv, respectively. Both observations showed clear diurnal variations, i.e., NH₃ reached daily maximum around 6:00—7:00 and then start decreasing to daily minimum around 15:00. Using positive matrix factorization (PMF), we performed source apportionment of NH₃ for both campaigns. The results showed that biomass burning for heat generation and automobile exhausts were the most important emission sources of NH₃. For each individual year, specifically, biomass burning contributed about 66.0% and 55.0% of the observed NH₃; automobile exhausts accounted for 27.0% and 36.8%; 6.2% and 7.5% of the total were due to domestic activities, such as soil emissions and sewages; long-distance transport accounted for a small percentage, 0.8% and 0.7%, respectively. From 2017 to 2018, the wintertime NH₃ decreased significantly due to the implementation of air pollution abatement strategies, despite the fact that biomass burning was still the dominant source of NH₃, which should be further strictly controlled in the future.

• Key words：ammonia  proton transfer reaction mass spectrometry  PMF  agriculture emission  North China Plain

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