Project Outline

Volatile reactive nitrogen oxides (NOy), comprised of NOx (NO + NO₂) and NOz (HONO + HNO₃ + N₂O₅ + …), negatively impact air quality as they are precursors to smog and acid rain, modify climate by enhancing concentrations of tropospheric ozone (O₃), and can exacerbate respiratory issues such as asthma, acute bronchitis, and chronic obstructive pulmonary disease – especially in adolescent and geriatric populations (1). NOy can also react on heterogeneous surfaces, such as aerosols, eventually being deposited in terrestrial, aquatic, or marine ecosystems – a process shown to contribute to plant community change as well as aquatic eutrophication (2). Very little is known about NOy fluxes from natural sources, even though these sources account for over a half of all atmospheric NOy. Soil is the dominant natural contributor (24%), with this percentage increasing as vehicle and industry emissions decline (3). As NOy are relatively short-lived, chemical lifetime ~ 20 mins for nitrous acid (HONO) and up to 18 hours for nitrogen dioxide (NO₂), their concentration profiles tend to be localised and consistent depending on the environment (4). Sources and sinks of NOy are important in addressing air quality and developing reliable policy, where government policy changes may not produce expected result due to these natural sources. Importantly, descriptions of soil NOy emissions (especially NO₂ and HONO) in climate models are non-existent, due to a lack of data regarding the mechanisms that control NOy fluxes from soil. Most research on ground-level NOy sources has focused on identifying abiotic mechanisms; however, far less work has been done to elucidate biogenic contributions, resulting in a significant omission in climate models. Agricultural areas have been shown to be major contributors to soil NOy emissions, due to fertiliser use, irrigation, and soil disturbance (5,6); however, mechanisms at the plant-soil-microbe interface have yet to be elucidated. By coupling field-based crop trials to robust chemical quantification and molecular analyses, we will test hypotheses regarding how a major agricultural crop, its soil, and associated soil microbes influence NOy fluxes.

References

1. Pitts et al. 2000. Chemistry of the Upper and Lower Atmosphere pp. 264-93.
2. Field et al. 2014. The role of nitrogen deposition in widespread plant community change across semi-natural habitats. Ecosystems 17: 864-77.
3. Fowler et al. 2013. The global nitrogen cycle in the twenty-first century. Philos Trans R Soc Lond B Biol. Sci. 368: 1621.
4. Li et al. 2012. Exploring the atmospheric chemistry of nitrous acid (HONO) at a rural site in Southern China. Atmos Chem Phys 12: 1497-1513.
5. Hudman et al. 2012. Steps towards a mechanistic model of global soil nitric oxide emissions: implementation and space based-constraints. Atmos Chem Phys 12: 7779-95.
6. Wang et al. 2021. Improved modelling of soil NOx emissions in a high temperature agricultural region: role of background emissions on NO2 trend over the US. Environ Res Let 16: 084061.

Techniques

Training during this fellowship includes a wide range of molecular techniques and analyses (microbial culturing, DNA extraction from soil, PCR, sequencing, and bioinformatics) as well as analytical chemistry (trace gas quantification, reactive mass spectrometry, and building sampling microcosms). Field-based cultivation and management of agricultural crops will also be likely.