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, 368 (1621), 20130166

Towards a Climate-Dependent Paradigm of Ammonia Emission and Deposition

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Towards a Climate-Dependent Paradigm of Ammonia Emission and Deposition

Mark A Sutton et al. Philos Trans R Soc Lond B Biol Sci.

Abstract

Existing descriptions of bi-directional ammonia (NH3) land-atmosphere exchange incorporate temperature and moisture controls, and are beginning to be used in regional chemical transport models. However, such models have typically applied simpler emission factors to upscale the main NH3 emission terms. While this approach has successfully simulated the main spatial patterns on local to global scales, it fails to address the environment- and climate-dependence of emissions. To handle these issues, we outline the basis for a new modelling paradigm where both NH3 emissions and deposition are calculated online according to diurnal, seasonal and spatial differences in meteorology. We show how measurements reveal a strong, but complex pattern of climatic dependence, which is increasingly being characterized using ground-based NH3 monitoring and satellite observations, while advances in process-based modelling are illustrated for agricultural and natural sources, including a global application for seabird colonies. A future architecture for NH3 emission-deposition modelling is proposed that integrates the spatio-temporal interactions, and provides the necessary foundation to assess the consequences of climate change. Based on available measurements, a first empirical estimate suggests that 5°C warming would increase emissions by 42 per cent (28-67%). Together with increased anthropogenic activity, global NH3 emissions may increase from 65 (45-85) Tg N in 2008 to reach 132 (89-179) Tg by 2100.

Keywords: ammonia; atmospheric modelling; deposition; emission.

Figures

Figure 1.
Figure 1.
Simulated changes in N deposition in eastern USA, showing the ratios for 2020/2001 (adapted from Pinder et al. [5]). (a) Oxidized N deposition, (b) reduced N deposition and (c) total N deposition.
Figure 2.
Figure 2.
Spatial variability in global ammonia emissions based on JRC/PBL [34] (livestock, fertilizers, biomass burning, fuel consumption) and Riddick et al. [35] (seabirds). Emissions from oceans, humans, pets, natural soils and other wild animals (table 1) are not mapped. High-resolution maps for the UK are given in the electronic supplementary material, figure S1.
Figure 3.
Figure 3.
Resistance analogue of NH3 exchange including cuticular, stomatal and ground pathways. Two schemes for cuticular exchange are illustrated: scheme 1, steady-state uptake according to a varying cuticular resistance (Rw); scheme 2, dynamic exchange with a pool of NH4+ treated with varying capacitance (Cd) and charge (Qd). Other resistances are for turbulent atmospheric transfer (Ra), the quasi-laminar boundary layer (Rb), within-canopy transfer (Rac), cuticular adsorption/desorption (Rd) and stomatal exchange (Rs). Also shown are the air concentration (χa), cuticular concentration (χd), stomatal compensation point (χs), litter/soil surface concentration (χl) and the canopy compensation point (χc). Exchange between aqueous NH4+ pools is shown with dashed lines, including Kr, the exchange rate between leaf surface and apoplast.
Figure 4.
Figure 4.
Effect of temperature scenarios (annual change of +3°C and −3°C) on (a) simulated nitrogen pools (foliar substrate N, and Γs) and (b) net NH3 fluxes. Simulations conducted using the PaSim model for managed grassland in Scotland following cutting and fertilization with ammonium nitrate.
Figure 5.
Figure 5.
Satellite estimates of the NH3 column (106 molecules cm−2) and ground temperature, showing the mean for 2009, 2010 and 2011 (from the infrared atmospheric sounding interferometer on the MetOp platform), as compared with ground-based measurements of atmospheric NH3 concentrations at three selected sites.
Figure 6.
Figure 6.
Measured percentage of excreted Nr that is volatilized as NH3 (Pv) as a function of mean temperature during field campaigns (dashed line: Pv(%) = 1.9354e0.109 T; R2 = 0.75), as compared with estimates from the GUANO model for a global selection of seabird colonies. The dotted line shows the value used in a first bioeneregics (BE) model of Blackall et al. [59], while the solid line was applied in a temperature-adjusted bioenergetics (TABE) model, by Riddick et al. [35] using equation (3.3). The bars on the measured points apply to colonies including burrow-nesting birds and indicate the estimated Pv if the colony were entirely populated by bare-rock breeders.
Figure 7.
Figure 7.
Global application of the GUANO model illustrating the average percentage of excreted N that is volatilized as NH3. Excretion calculated based on colony seabird energetics [35], combined with hourly meteorological estimates through 2010–2011.
Figure 8.
Figure 8.
Proposed modelling architecture for treating the climate-dependence of ammonia fluxes in regional and global atmospheric transport and chemistry models. In this approach, static emission inventories are replaced by calculations depending on prevailing meteorology, while allowing for bi-directional exchange with area sources/sinks, giving the basis to assess climate change scenarios including the consequences of climate feedbacks through altered NH3 emissions. The effect of altered air chemistry may also be fed back into the climate model.

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