Nitrogen oxide and radical reservoir species in the troposphere

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The goal of this research program is to improve the scientific understanding of chemical processes in the troposphere (the lowest layer of the atmosphere) that control the abundances of ozone (O3) and secondary organic aerosol (SOA), which in high concentration adversely affect human health and the Earth's climate. Tropospheric O3 production occurs through photo-oxidation of volatile organic compounds (VOC) via the NOx (=NO+NO2) and HOx (=OH+HO2) catalytic radical chains. This research program seeks to remove uncertainties in the production, removal, and transport (in the form of reservoir species) of NOx and HOx radicals. Alkyl nitrates (organic compounds containing the -ONO2 group) are critical in this context because they act either as reservoir species, temporarily storing NOx and redistributing it around the globe, or as NOx sinks, permanently removing it through hydrolysis to nitric acid, a major component of acid rain. Because alkyl nitrates are less volatile than their VOC precursors, their formation is also linked to SOA growth. However, many details have not been worked out (e.g., air-water partitioning coefficients), in particular for alkyl nitrates derived from biogenic VOC. We will accomplish our research objectives through novel, one-of-a-kind analytical methods and conduct laboratory experiments to investigate the chemistry of organic nitrates and of free radicals and their reservoir species, including nitrous acid, organic peroxy radicals, and chlorine nitrate (ClNO3). We will use methods pioneered in my lab, e.g., cavity ring-down and cavity-enhanced absorption spectroscopy, to systematically study alkyl nitrates derived from both anthropogenic and biogenic sources. Specifically, we will measure their yields in reactions between RO2 with NO () and unsaturated VOCs with NO3, determine their Henry's law constants, quantify the amount of NOx recycled when they are reacted with OH radicals (), and measure their aerosol uptake parameters (). We will also investigate heterogeneous photo-oxidation processes which are considerably altered by photosensitizers such as the only recently recognized imidazoles. Results from these laboratory studies will be parameterized for incorporation into atmospheric models. In addition, we will construct a peroxy-radical chemical amplifier (PERCA) to detect peroxide explosives. These are readily synthesized using household chemicals but currently escape trace vapor detection by routine methods. The information that this research program will provide will allow policy makers and stakeholders to make more informed decisions on pollution control strategies. The benefits to Canadians will be the training of experts to assist in this process. A reduction of environmental impacts of anthropogenic activities will have economic benefits to society though improved health and a reduced climate impact.