Addressing gaps in estimates of NOx from California agricultural land

Authors: ZHU-BARKER, XIA - University Of California, Davis; Venterea, Rodney - Rod; BURGER, MARTIN - California Department Of Food And Agriculture; HORWATH, WILLIAM - University Of California, Davis

Submitted to: Science Advances
Publication Type: Other
Publication Acceptance Date: 4/13/2018
Publication Date: 5/25/2018
Citation: Zhu-Barker, X., Venterea, R.T., Burger, M., Horwath, W. 2018. Addressing gaps in estimates of NOx from California agricultural land. Science Advances. 4(1). 10.1126/sciadv.aao3477.
DOI: https://doi.org/10.1126/sciadv.aao3477

Interpretive Summary: Understanding the contribution of farming to nitric oxides (NOx) pollution in California and other agricultural regions is critical to developing fertilizer nitrogen (N) management guidelines that consider food security and environmental impact as agricultural production becomes increasingly intensified. Almaraz et al (Science Advances, 31 Jan 2018) reports that NOx fluxes from agricultural land may be a much larger source of NOx in California than is currently recognized. Using two independent approaches, i.e. a bottom-up spatial mass balance model and top-down airborne observation combined with the California emissions projection analysis model, Almaraz et al. showed that agricultural soils are a dominant source of NOx pollution in California, which is estimated to increase the current state NOx budget by 20-51%. However, this conclusion is challenged by the lack of uncertainties that are associated with model implementation and validation, as well as by the lack of accurate depiction of processes and factors that contribute to NOx production in the model. This report is interesting and timely because it brings NOx emissions from California agriculture to the forefront of current issues, and it is the first attempt to quantify those emissions at the state level. However, while we agree with the overall conclusion that agricultural soils need to be reevaluated as an important statewide NOx source, we also argue here that the absolute emission values reported are not qualified by appropriate uncertainty analysis and are clouded by unclear procedures. These limitations preclude conclusive acceptance of the reported emissions values as reliable estimates of the statewide agricultural NOx inventory. This information will be informative to scientists, land-managers and policy-makers interested in developing improved land management practices to reduce pollution while enhancing agricultural production capacity.

Technical Abstract: Understanding the contribution of farming to nitric oxides (NOx) pollution in California and other agricultural regions is critical to developing fertilizer nitrogen (N) management guidelines that consider food security and environmental impact as agricultural production becomes increasingly intensified. Almaraz et al (Science Advances, 31 Jan 2018) report that NOx fluxes from agricultural land may be a much larger source of NOx in California than is currently recognized. Using two independent approaches, i.e. a bottom-up spatial mass balance model and top-down airborne observation combined with the California emissions projection analysis model, Almaraz et al. showed that agricultural soils are a dominant source of NOx pollution in California, which is estimated to increase the current state NOx budget by 20-51%. However, this conclusion is challenged by the lack of uncertainties that are associated with model implementation and validation, as well as by the lack of accurate depiction of processes and factors that contribute to NOx production in the model. This report is interesting and timely because it brings NOx emissions from California agriculture to the forefront of current issues, and it is the first attempt to quantify those emissions at the state level. However, while we agree with the overall conclusion that agricultural soils need to be reevaluated as an important statewide NOx source, we also argue here that the absolute emission values reported are not qualified by appropriate uncertainty analysis and are clouded by unclear procedures. These limitations preclude conclusive acceptance of the reported emissions values as reliable estimates of the statewide agricultural NOx inventory.