Nitrogen Oxide Isotopes for Soil Emissions (NOISE)

Nitrogen oxides (NOx = NO + NO2) are both a direct air pollutant and play a central role in the atmospheric chemistry controlling the removal of emitted gases and the production of secondary pollutants. Understanding NOx emissions both now and into the future is therefore essential if we are to tackle environmental challenges such as air pollution, climate and acid deposition. In many parts of the globe dramatic reductions in NOx emissions from road transport is resulting in current and projected NOx source profiles being unrecognisable from those of 20 years ago. Although something to be celebrated, this has resulted in a large and growing uncertainty in projections of future atmospheric change because the data on which current and future atmospheric emissions inventories and policy projections are based are no longer relevant. Several recent studies have suggested that heavily fertilised agricultural soils could now be a major source of NOx in many highly populated regions. If correct, the fact that these sources are vastly underestimated in current emissions inventories represents a critical flaw in atmospheric projections and a major omission from the current environmental policy agenda. This flaw is only going to grow as combustion sources of NOx continue to decrease, and therefore real-world observations that can constrain current NOx sources and support updates to current and future emission inventories are urgently needed. NOISE will take two approaches to address this urgent research need: By generating the most comprehensive dataset to-date on the biogeochemical drivers of soil NOx production we will develop a process-based parameterisation of soil NOx emission. Previous work has lacked the required observations to constrain such a parameterisation, but our extensive laboratory and field studies will enable the identification of the key microbial players in reactive nitrogen production and isolate effects of environmental factors on both NOx production and NOx isotopic fractionation. This soil NOx emission parameterisation will represent a significant advance over those used in current models that advise emission inventories and policy. Develop and demonstrate a robust observational method to assess the soil NOx contribution to ambient NOx levels, thus directly addressing the large variability reported in the literature. This will be achieved through the development of novel analytical technology capable of accurately measuring NOx isotopes at high time resolution. This approach represents a significant advance over previous methods as our advanced analytical technique enables real-world variability in isotopic signatures to be quantified and thus accounted for during the source apportionment. A unique strength of this project is the combination of world-leading expertise in atmospheric chemistry and microbial biogeochemistry, enabling a holistic approach to tackling a complex problem. Ultimately, NOISE will deliver a step-change in both the parameterisation of soil NOx emissions and our ability to validate these estimates, thus laying the foundations for significantly reducing a major uncertainty in predictions of future atmospheric change during the most radical change in NOx emissions since the industrial revolution.