Collaborative Research: Particulate Nitrate Photolysis as a Daytime Nitrous Acid Source and a Reactive Nitrogen Recycling Pathway in the Troposphere

本项目将研究以下假设：在地表边界层以上对流层低氮氧化物条件下，气溶胶颗粒中硝酸盐的光解和有机气溶胶中二氧化氮的转化是亚硝酸(HONO)的主要白天来源。由于HONO很容易被光解为羟基自由基(OH)和一氧化氮，进一步假设气溶胶粒子中的颗粒硝酸盐(PNO3)的光解是将硝酸/硝酸盐循环回对流层中具有光化学反应活性的氮氧化物的重要途径。将开展一系列研究活动，包括现场测量、实验室实验和建模。具体来说：*将在美国国家科学基金会/国家大气研究中心C-130研究机的飞行过程中进行测量，以确定美国东南部和邻近沿海水域背景大陆和海洋气团中HONO的浓度分布，并建立白天HONO生成量与其他物理化学参数之间的关系，包括pNO3、颗粒有机物、二氧化氮、臭氧、气溶胶颗粒表面积和太阳辐射。*从C-130收集的气溶胶样本将用于实验室实验，以确定过滤器上气溶胶pNO3光解产生HONO的速率。*模型计算将基于现场测量和实验室实验的结果，研究pNO3光解和二氧化氮在作为HONO来源的有机气溶胶上的吸收，并研究pNO3光解是否是硝酸/硝酸盐再循环的有效途径，以及*评估这一过程在对流层光化学中的作用。这项研究将提供关于对流层中HONO、硝酸、pNO3和其他相关参数的垂直分布的信息。如果上述两个假设被证明是有效的，就会有重大的大气影响：对流层的光化学反应可能比通常预测的更大，这是由于可再动员的HONO和氮氧化物以及升高的OH水平，通常导致臭氧和次级粒子的产生增加。因此，这项研究可以大大提高我们对区域和全球范围内对流层反应氮化学和大气氧化能力的理解。该项目还将为大气化学领域的博士后研究人员、研究生、本科生和高中生提供研究和培训机会。这项研究还涉及更大的空气质量和全球气候变化问题，即研究结果将提供有关大气氧化能力的有用信息，从而深入了解包括一些温室气体在内的大气污染物是如何被降解的。

This project will investigate the hypothesis that photolysis of particulate nitrate in aerosol particles, and to a lesser extent nitrogen dioxide conversion on organic aerosols, are major daytime sources of nitrous acid (HONO) under low nitrogen oxide conditions in the troposphere above the surface boundary layer. Since HONO is readily photolyzed to hydroxyl radical (OH) and nitric oxide, it is further hypothesized that photolysis of particulate nitrate (pNO3) in aerosol particles represents an important pathway to recycle nitric acid/nitrate back to photochemically reactive nitrogen oxides in the troposphere. A series of research activities will be undertaken involving field measurements, laboratory experiments and modeling. Specifically:* Measurements will be made during flights of the NSF/National Center for Atmospheric Research C-130 research aircraft to establish HONO concentration distributions in background continental and oceanic air masses over the southeastern U.S and adjacent coastal waters and to establish relationships between the daytime HONO production and other physical and chemical parameters, including pNO3, particulate organic matter, nitrogen dioxide, ozone, aerosol particle surface area, and solar radiation.* Aerosol samples collected from the C-130 will be used in laboratory experiments to determine the HONO production rate from the photolysis of aerosol pNO3 on filters.* Model calculations will be done based on the results of field measurements and laboratory experiments, to examine pNO3 photolysis and nitrogen dioxide uptake on organic aerosol as a HONO source and investigate if pNO3 photolysis is an efficient re-recycling pathway for nitric acid/nitrate, and* To evaluate the role of this processes in tropospheric photochemistryThe research will provide information on the vertical distribution of HONO, nitric acid, pNO3 and other relevant parameters in the troposphere. If the above two hypotheses are proven valid, there are significant atmospheric implications: The troposphere may be more photochemically reactive than generally predicted, due to the remobilized HONO and nitrogen oxides as well as elevated OH levels, generally leading to an enhanced production of ozone and secondary particles. The research may therefore significantly improve our understanding of tropospheric reactive nitrogen chemistry and atmospheric oxidation capacity on regional and global scales. The project will also provide research and training opportunities for postdoctoral researchers, graduate, undergraduate, and high school students in the field of atmospheric chemistry. The research is also relevant to the larger question of air quality and global climate change, i.e., the results from the research will provide useful information regarding atmospheric oxidation capacity and thus insights into how atmospheric pollutants, including some greenhouse gases, are degraded.