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

该项目将研究这样一种假设，即在表面边界层以上的对流层中，在低氮氧化物条件下，气溶胶颗粒中硝酸盐颗粒的光解作用，以及有机气溶胶中二氧化氮的较小程度的转化，是白天亚硝酸（HONO）的主要来源。由于HONO很容易被光解为羟基自由基（OH）和一氧化氮，因此进一步假设气溶胶颗粒中硝酸颗粒（pNO3）的光解是将硝酸/硝酸盐再循环回对流层中光化学反应性氮氧化物的重要途径。将进行一系列研究活动，包括实地测量、实验室实验和建模。具体而言：*测量将在NSF/国家大气研究中心C-130研究飞机飞行期间进行，以建立美国东南部和邻近沿海水域背景大陆和海洋气团的HONO浓度分布，并建立白天HONO产生与其他物理和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，还有太阳辐射。*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。*将根据实地测量和实验室实验的结果进行模式计算，以检验有机气溶胶作为HONO来源的pNO3光解和二氧化氮吸收，并研究pNO3光解是否为硝酸/硝酸盐的有效再循环途径，以及*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pNO3及其他相关参数。如果上述两种假设被证明是有效的，将对大气产生重大影响：由于HONO和氮氧化物的再活化以及OH水平的升高，对流层的光化学反应可能比一般预测的更强烈，这通常会导致臭氧和二次粒子的产生增加。因此，这项研究可能会显著提高我们对对流层活性氮化学和大气氧化能力在区域和全球尺度上的认识。该项目还将为大气化学领域的博士后、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，从而深入了解包括一些温室气体在内的大气污染物是如何降解的。

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.