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

本项目将调查以下假设：气溶胶颗粒中硝酸盐微粒的光分解，以及在较小程度上有机气溶胶中二氧化氮的转化，是地面边界层上方对流层中低氮氧化物条件下亚硝酸的主要日间来源。由于HONO很容易光解为羟基自由基（OH）和一氧化氮，因此进一步假设气溶胶颗粒中的微粒硝酸盐（pNO 3）的光解是将硝酸/硝酸盐再循环回对流层中的光化学反应性氮氧化物的重要途径。将开展一系列研究活动，包括实地测量、实验室实验和建模。具体而言：* 将在NSF/国家大气研究中心C-130研究飞机飞行期间进行测量，以确定美国东南部和邻近沿海沃茨上空背景大陆和海洋气团中的HONO浓度分布，并确定白天HONO产生与其他物理和化学参数之间的关系，包括pNO 3、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收集的气溶胶样品将用于实验室实验，以确定气溶胶pNO 3在过滤器上的光解产生HONO的速率。模式计算将根据现场测量和实验室实验的结果进行，以检查pNO 3光解和二氧化氮吸收的有机气溶胶作为HONO源，并调查pNO 3光解是否是一个有效的再循环途径硝酸/硝酸盐，* 评估这一过程在对流层光化学中的作用研究将提供有关HONO，硝酸，对流层中的pNO 3和其他相关参数。如果上述两个假设被证明是有效的，则有显著的大气影响：对流层可能比通常预测的更具光化学反应性，这是由于HONO和氮氧化物的再活化以及OH水平的升高，通常会导致臭氧和次级粒子的产生增加。因此，这项研究可能会显着提高我们的理解对流层活性氮化学和大气氧化能力的区域和全球范围内。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。这项研究也与空气质量和全球气候变化这一更大的问题有关，即，研究结果将提供有关大气氧化能力的有用信息，从而深入了解大气污染物，包括一些温室气体是如何降解的。

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.