Photo-oxidation and multiphase reactions of atmospheric reduced nitrogen

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While molecular N2 comprises 78% of Earth's atmosphere, it is nitrogen-containing molecules typically present at much lower levels (parts per billion or trillion) that have major impacts on the radiative budget and reactivity of the atmosphere. For example, nitrous oxide (N2O) is a potent and long-lived greenhouse gas, ammonia (NH3) controls the formation and growth of particulate matter, and nitrogen oxide radicals (NO and NO2) regulate the atmosphere's oxidative capacity. A substantial fraction of global food production relies on fixed nitrogen from industrial fertilizer, but the intervention of humans in the global biogeochemical cycle of nitrogen has a series of important consequences for society including degraded air quality, ozone depletion, acid rain, and eutrophication of water bodies. ****The overall goal of this research is to identify and quantify the rates of chemical transformations of fixed nitrogen within the atmosphere, and the rates of its exchange (emission/deposition) with underlying ecosystems.******While emissions of NO resulting from human activity are predicted to decline globally over the next century, emissions of NH3 are expected to continue increasing with fertilizer production. In that scenario, the oxidation of NH3 could become a significant source of NO to the atmosphere, transforming the way we think about the reactive nitrogen budget. To investigate the importance of this pathway, we need more accurate information about the rates and products of gas phase chemical reactions involved in the oxidation of NH3. Many of these reactions have been studied under conditions that are relevant to combustion systems but not to Earth's atmosphere. One particularly interesting aspect of this chemistry is the involvement of the molecule HNO, which no one has measured in the atmosphere before. We hypothesize that it should be present in measurable quantities and propose to develop a system to measure it in different environments.******Ammonia does not only react in the gas phase, but also in a range of condensed phases in the environment such as dew, fog, clouds, snow, aqueous aerosol and organic aerosol. We will create artificial systems in the lab to study potential reactions, and we will also collect fog, dew and aerosol samples from the environment and carry out the reactions in them. The investigations of this condensed phase chemistry will be extended to other forms of reduced nitrogen, such as amines and isocyanates, which can be involved in reactions producing toxic and/or light-absorbing compounds. For this reason, the research is relevant to understanding the health and climate implications of atmospheric reactive nitrogen.***********