Abstract
Abstract. Biogenic NO emissions from soils (SNOx) play important direct and indirect roles in tropospheric chemistry. The most widely applied algorithm to calculate SNOx in global models was published 15 years ago by Yienger and Levy (1995), and was based on very few measurements. Since then, numerous new measurements have been published, which we used to build up a compilation of world wide field measurements covering the period from 1978 to 2010. Recently, several satellite-based top-down approaches, which recalculated the different sources of NOx (fossil fuel, biomass burning, soil and lightning), have shown an underestimation of SNOx by the algorithm of Yienger and Levy (1995). Nevertheless, to our knowledge no general improvements of this algorithm, besides suggested scalings of the total source magnitude, have yet been published. Here we present major improvements to the algorithm, which should help to optimize the representation of SNOx in atmospheric-chemistry global climate models, without modifying the underlying principals or mathematical equations. The changes include: (1) using a new landcover map, with twice the number of landcover classes, and using annually varying fertilizer application rates; (2) adopting a fraction of 1.0 % for the applied fertilizer lost as NO, based on our compilation of measurements; (3) using the volumetric soil moisture to distinguish between the wet and dry states; and (4) adjusting the emission factors to reproduce the measured emissions in our compilation (based on either their geometric or arithmetic mean values). These steps lead to increased global annual SNOx, and our total above canopy SNOx source of 8.6 Tg yr−1 (using the geometric mean) ends up being close to one of the satellite-based top-down approaches (8.9 Tg yr−1). The above canopy SNOx source using the arithmetic mean is 27.6 Tg yr−1, which is higher than all previous estimates, but compares better with a regional top-down study in eastern China. This suggests that both top-down and bottom-up approaches will be needed in future attempts to provide a better calculation of SNOx.
Highlights
IntroductionMeasurements of the NO2 column from satellites have been used in “top-down” approaches to optimize emissions from various sources, including SNOx (Martin et al, 2003; Bertram et al, 2005; Jaegleet al., 2005; Muller and Stavrakou, 2005; Martin et al, 2006)
Nitrogen oxides (NOx = NO + NO2) play an important role in the chemical processes of the atmosphere, especially in the production and destruction of ozone (Chameides et al, 1992)
We have made significant improvements to the soil NO emission algorithm developed by Yienger and Levy (1995) using a much larger set of in situ measurements, along with several other recent advances such as more detailed land cover classifications
Summary
Measurements of the NO2 column from satellites have been used in “top-down” approaches to optimize emissions from various sources, including SNOx (Martin et al, 2003; Bertram et al, 2005; Jaegleet al., 2005; Muller and Stavrakou, 2005; Martin et al, 2006). We present major improvements to the algorithm by YL95 and derive updated emission factors, which could be used in other models as well. These new emission factors are calibrated in a bottom-up approach with a global compilation of measurements of SNOx. We compare our simulated emissions to the a posteriori top-down emissions of Jaegleet al. We compare our simulated emissions to the a posteriori top-down emissions of Jaegleet al. (2005), and discuss them in the context of other top-down studies by Muller and Stavrakou (2005), Wang et al (2007), Stavrakou et al (2008), and Zhao and Wang (2009)
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