scholarly journals Exploring the sensitivity of atmospheric nitrate concentrations to nitric acid uptake rate using the Met Office's Unified Model

2021 ◽  
Vol 21 (20) ◽  
pp. 15901-15927
Author(s):  
Anthony C. Jones ◽  
Adrian Hill ◽  
Samuel Remy ◽  
N. Luke Abraham ◽  
Mohit Dalvi ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Ammonium Nitrate ◽  
Thermodynamic Equilibrium ◽  
Unified Model ◽  
Limiting Factor ◽  
Acid Uptake ◽  
Fast Simulation ◽  
Near Surface ◽  
Uptake Rates ◽  
Nitrate Concentrations

Abstract. Ammonium nitrate is a major aerosol constituent over many land regions and contributes to air pollution episodes, ecosystem destruction, regional haze, and aerosol-induced climate forcing. Many climate models that represent ammonium nitrate assume that the ammonium–sulfate–nitrate chemistry reaches thermodynamic equilibrium instantaneously without considering kinetic limitations on condensation rates. The Met Office's Unified Model (UM) is employed to investigate the sensitivity of ammonium nitrate concentrations to the nitric acid uptake coefficient (γ) in a newly developed nitrate scheme in which first-order condensation theory is utilised to limit the rate at which thermodynamic equilibrium is attained. Two values of γ representing fast (γ=0.193) and slow (γ=0.001) uptake rates are tested in 20-year global UM integrations. The global burden of nitrate associated with ammonium in the “fast” simulation (0.11 Tg[N]) is twice as great as in the “slow” simulation (0.05 Tg[N]), while the top-of-the-atmosphere radiative impact of representing nitrate is −0.19 W m−2 in the fast simulation and −0.07 W m−2 in the slow simulation. In general, the fast simulation exhibits better spatial correlation with observed nitrate concentrations, while the slow simulation better resolves the magnitude of concentrations. Local near-surface nitrate concentrations are found to be highly correlated with seasonal ammonia emissions, suggesting that ammonia is the predominant limiting factor controlling nitrate prevalence. This study highlights the high sensitivity of ammonium nitrate concentrations to nitric acid uptake rates and provides a novel mechanism for reducing nitrate concentration biases in climate model simulations. The new UM nitrate scheme represents a step change in aerosol modelling capability in the UK across weather and climate timescales.

scholarly journals Exploring the sensitivity of atmospheric nitrate concentrations to nitric acid uptake rate using the Met Office's Unified Model

2021 ◽  
Author(s):  
Anthony C. Jones ◽  
Adrian Hill ◽  
Samuel Remy ◽  
N. Luke Abraham ◽  
Mohit Dalvi ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Ammonium Nitrate ◽  
Thermodynamic Equilibrium ◽  
Unified Model ◽  
Limiting Factor ◽  
Acid Uptake ◽  
Fast Simulation ◽  
Near Surface ◽  
Uptake Rates ◽  
Nitrate Concentrations

Abstract. Ammonium nitrate is a major aerosol constituent over many land regions and contributes to air pollution episodes, ecosystem destruction, regional haze, and aerosol-induced climate forcing. Many climate models that represent ammonium nitrate assume that the ammonium-sulphate-nitrate chemistry reaches thermodynamic equilibrium instantaneously without considering kinetic limitations on condensation rates. The Met Office's Unified Model (UM) is employed to investigate the sensitivity of ammonium nitrate concentrations to the nitric acid uptake coefficient (γ) in a newly-developed nitrate scheme in which first order condensation theory is utilised to limit the rate at which thermodynamic equilibrium is attained. Two values of γ representing fast (γ = 0.193) and slow (γ = 0.001) uptake rates are tested in 20-year global UM integrations. The global burden of nitrate associated with ammonium in the “fast” simulation (0.11 Tg[N]) is twice as great as in the “slow” simulation (0.05 Tg[N]), while the top-of-the-atmosphere radiative impact of representing nitrate is −0.19 Wm−2 in the “fast” simulation and −0.07 Wm−2 in the “slow” simulation. In general, the “fast” simulation exhibits better spatial correlation with observed nitrate concentrations while the “slow” simulation better resolves the magnitude of concentrations. Local near-surface nitrate concentrations are found to be highly correlated with seasonal ammonia emissions suggesting that ammonia is the predominant limiting factor controlling nitrate prevalence. This study highlights the high sensitivity of ammonium nitrate concentrations to nitric acid uptake rates and provides a mechanism for reducing nitrate concentration biases in climate model simulations. The new UM nitrate scheme represents a step-change in aerosol modelling capability in the UK across weather and climate timescales.

scholarly journals Sensitivity of nitrate aerosols to ammonia emissions and to nitrate chemistry: implications for present and future nitrate optical depth

2016 ◽  
Vol 16 (3) ◽  
pp. 1459-1477 ◽  
Author(s):  
F. Paulot ◽  
P. Ginoux ◽  
W. F. Cooke ◽  
L. J. Donner ◽  
S. Fan ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Heterogeneous Reaction ◽  
Convective Transport ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Ammonia Emissions ◽  
Near Surface ◽  
Nitrate Concentrations ◽  
The Impact

Abstract. We update and evaluate the treatment of nitrate aerosols in the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model (AM3). Accounting for the radiative effects of nitrate aerosols generally improves the simulated aerosol optical depth, although nitrate concentrations at the surface are biased high. This bias can be reduced by increasing the deposition of nitrate to account for the near-surface volatilization of ammonium nitrate or by neglecting the heterogeneous production of nitric acid to account for the inhibition of N2O5 reactive uptake at high nitrate concentrations. Globally, uncertainties in these processes can impact the simulated nitrate optical depth by up to 25 %, much more than the impact of uncertainties in the seasonality of ammonia emissions (6 %) or in the uptake of nitric acid on dust (13 %). Our best estimate for fine nitrate optical depth at 550 nm in 2010 is 0.006 (0.005–0.008). In wintertime, nitrate aerosols are simulated to account for over 30 % of the aerosol optical depth over western Europe and North America. Simulated nitrate optical depth increases by less than 30 % (0.0061–0.010) in response to projected changes in anthropogenic emissions from 2010 to 2050 (e.g., −40 % for SO2 and +38 % for ammonia). This increase is primarily driven by greater concentrations of nitrate in the free troposphere, while surface nitrate concentrations decrease in the midlatitudes following lower concentrations of nitric acid. With the projected increase of ammonia emissions, we show that better constraints on the vertical distribution of ammonia (e.g., convective transport and biomass burning injection) and on the sources and sinks of nitric acid (e.g., heterogeneous reaction on dust) are needed to improve estimates of future nitrate optical depth.

scholarly journals Secondary inorganic aerosol simulations for Europe with special attention to nitrate

2004 ◽  
Vol 4 (3) ◽  
pp. 857-874 ◽  
Author(s):  
M. Schaap ◽  
M. van Loon ◽  
H. M. ten Brink ◽  
F. J. Dentener ◽  
P. J. H. Builtjes
Keyword(s):  
Seasonal Variation ◽  
Nitric Acid ◽  
Ammonium Nitrate ◽  
Model Simulation ◽  
Volatile Component ◽  
Sea Salt ◽  
Heterogeneous Reactions ◽  
Aerosol Formation ◽  
High Ammonia ◽  
Nitrate Concentrations

Abstract. Nitrate is an important component of (secondary inorganic) fine aerosols in Europe. We present a model simulation for the year 1995 in which we account for the formation of secondary inorganic aerosols including ammonium sulphate and ammonium nitrate, a semi volatile component. For this purpose, the chemistry-transport model LOTOS was extended with a thermodynamic equilibrium module and additional relevant processes to account for secondary aerosol formation and deposition. During winter, fall and especially spring high nitrate levels are projected over north western, central and eastern Europe. During winter nitrate concentrations are highest in Italy, in accordance with observed data. In winter nitric acid, the precursor for aerosol nitrate is formed through heterogeneous reactions on the surface of aerosols. Modelled and observed sulphate concentrations show little seasonal variation. Compared to sulphate levels, appreciable ammonium nitrate concentrations in summer are limited to those areas with high ammonia emissions, e.g. the Netherlands, since high ammonia concentrations are necessary to stabilise this aerosol component at high temperatures. As a consequence of the strong seasonal variation in nitrate levels the AOD depth of nitrate over Europe is especially significant compared to that of sulphate in winter and spring when equal AOD values are calculated over large parts of Europe. Averaged over all stations the model reproduces the measured concentrations for NO3, SO4, NH4, TNO3 (HNO3+NO3), TNH4 (NH3+NH4) and SO2 within 20%. The daily variation is captured well, albeit that the model does not always represent the amplitude of single events. The model underestimates wet deposition which was attributed to the crude representation of cloud processes. Comparison of retrieved and computed aerosol optical depth (AOD) showed that the model underestimates AOD significantly, which was expected due to the lack of carbonaceous aerosols, sea salt and dust in the model. The treatment of ammonia was found to be a major source for uncertainties in the model representation of secondary aerosols. Also, inclusion of sea salt is necessary to properly assess the nitrate and nitric acid levels in marine areas.

scholarly journals The nitrate aerosol field over Europe: simulations with an atmospheric chemistry-transport model of intermediate complexity

2003 ◽  
Vol 3 (6) ◽  
pp. 5919-5976 ◽  
Author(s):  
M. Schaap ◽  
M. van Loon ◽  
H. M. ten Brink ◽  
F. J. Dentener ◽  
P. J. H. Builtjes
Keyword(s):  
Nitric Acid ◽  
The Netherlands ◽  
Ammonium Nitrate ◽  
Transport Model ◽  
Chemistry Transport Model ◽  
Intermediate Complexity ◽  
High Ammonia ◽  
Nitrate Concentrations ◽  
The Impact ◽  
North Western

Abstract. Nitrate is an important component of fine aerosols in Europe. We present a model simulation for the year 1995 in which we account for the formation of the ammonium nitrate, a semi volatile component. For this purpose, LOTOS, a chemistry-transport model of intermediate complexity, was extended with a thermodynamic equilibrium module and additional relevant processes to account for aerosol formation and deposition. Our earlier analysis of data on (ammonium) nitrate in Europe was used for model evaluation. During winter, fall and especially spring high nitrate levels are projected over north western, central and eastern Europe. During winter nitrate concentrations are highest in the Po valley, Italy. This is in accordance with the field that was constructed from the data. In winter nitric acid, the precursor for aerosol nitrate, is formed through heterogeneous reactions on the surface of aerosols. Appreciable ammonium nitrate concentrations in summer are limited to those areas with high ammonia emissions, e.g. The Netherlands, since high ammonia concentrations are necessary to stabilise this aerosol component at high temperatures. Averaged over all stations the model reproduces the measured concentrations for NO3, SO4, NH4, TNO3, TNH4 and SO2 within 20%. The daily variation is captured well, albeit that the model does not always represents the amplitude of single events. The model underestimates wet deposition which was attributed to the crude representation of cloud processes. The treatment of ammonia was found to be the major source for uncertainties in the model representation of secondary aerosols. Also, inclusion of sea salt is necessary to properly assess the nitrate and nitric acid levels in marine areas. Over Europe the annual forcing by nitrate is calculated to be 25% of that by sulphate. In summer nitrate is found to be regionally important, e.g. in The Netherlands, where the forcing of nitrate and sulphate are calculated to be equal. In winter, spring and fall the nitrate forcing over Europe is about half that by sulphate. Over north western Europe and the alpine region the forcing by nitrate was calculated to be similar to that of sulphate. Overall, nitrate forcing is significant and should be taken into account to estimate the impact of regional climate change in Europe.

scholarly journals Sensitivity of nitrate aerosols to ammonia emissions and to nitrate chemistry: implications for present and future nitrate optical depth

2015 ◽  
Vol 15 (18) ◽  
pp. 25739-25788 ◽  
Author(s):  
F. Paulot ◽  
P. Ginoux ◽  
W. F. Cooke ◽  
L. J. Donner ◽  
S. Fan ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Atmospheric Model ◽  
Geophysical Fluid Dynamics Laboratory ◽  
Ammonia Emissions ◽  
Free Troposphere ◽  
Near Surface ◽  
Nitrate Concentrations ◽  
The Impact

Abstract. We update and evaluate the treatment of nitrate aerosols in the Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric model (AM3). Accounting for the radiative effects of nitrate aerosols generally improves the simulated aerosol optical depth, although nitrate concentrations at the surface are biased high. This bias can be reduced by increasing the deposition of nitrate to account for the near-surface volatilization of ammonium nitrate or by neglecting the heterogeneous production of nitric acid to account for the inhibition of N2O5 reactive uptake at high nitrate concentrations. Globally, uncertainties in these processes can impact the simulated nitrate optical depth by up to 25 %, much more than the impact of uncertainties in the seasonality of ammonia emissions (6 %) or in the uptake of nitric acid on dust (13 %). Our best estimate for present-day fine nitrate optical depth at 550 nm is 0.006 (0.005–0.008). We only find a modest increase of nitrate optical depth (< 30 %) in response to the projected changes in the emissions of SO2 (−40 %) and ammonia (+38 %) from 2010 to 2050. Nitrate burden is projected to increase in the tropics and in the free troposphere, but to decrease at the surface in the midlatitudes because of lower nitric acid concentrations. Our results suggest that better constraints on the heterogeneous chemistry of nitric acid on dust, on tropical ammonia emissions, and on the transport of ammonia to the free troposphere are needed to improve projections of aerosol optical depth.

Improving the global modeling of soils in JULES and the Unified Model: Updating from UM/HWSD to SoilGrids soil properties and from the Brooks & Corey to the van Genuchten soil-hydraulics model

2021 ◽  
Author(s):  
Patrick C. McGuire ◽  
Pier Luigi Vidale ◽  
Martin J. Best ◽  
David H. Case ◽  
Imtiaz Dharssi ◽  
...  
Keyword(s):  
Soil Properties ◽  
Land Surface ◽  
Climate Model ◽  
Model Updating ◽  
Unified Model ◽  
Pedotransfer Functions ◽  
Hydraulic Parameters ◽  
Near Surface ◽  
Soil Database ◽  
Soil Hydraulic

&lt;p&gt;&amp;#160;&amp;#160;&amp;#160; We have updated the soil properties used in JULES (Joint UK Land Environment Simulator), which is the land-surface component of the UM (Unified Model, the UK Met Office&amp;#8217;s climate model). JULES models the interaction of the land surface with the atmosphere, and simulates the energy, water, and carbon fluxes. JULES allows either: (i) the Brooks &amp; Corey (BC) model for estimating soil hydraulic properties, or (ii) the van Genuchten (VG) model but using hydraulic parameters translated from the BC model. One advantage of the VG model over the BC model is the smoother dependence of water retention upon matric potential for nearly saturated soils. Herein, we report on our work towards fully implementing the VG model in JULES and in the UM, through the implementation and evaluation of several VG pedotransfer functions (PTFs) for estimating the soil hydraulic parameters used in the hydraulic functions.&lt;/p&gt; &lt;p&gt;&amp;#160;&amp;#160;&amp;#160; We have tested three VG PTFs in global offline JULES runs (driven with WFDEI data over 1979-2012): the combination of T&amp;#243;th et al. PTFs 17 &amp; 20, the Weynants et al. PTF, and the Zhang &amp; Schaap ROSETTA3 H1 PTF (modified for sandy soils). We also modernized the soil basic properties that are conventionally used for JULES and the UM, from the UM version of the Harmonized World Soil Database (HWSD) to the SoilGrids database.&lt;/p&gt; &lt;p&gt;&amp;#160;&amp;#160;&amp;#160; Evaluation of JULES simulations shows (i) that the modified version of the Zhang &amp; Schaap ROSETTA3 H1 PTF is the best VG option, and (ii) that it compares favorably with the BC control model (which uses the Cosby et al. PTF and the UM/HWSD soils), in terms of the surface energy balance and the mitigation of near-surface temperature biases over mid-latitude continental regions. This modified version of the Zhang &amp; Schaap ROSETTA3 H1 PTF with SoilGrids soils is also currently being used in coupled land-atmosphere UM runs.&lt;/p&gt;

The Chemical Behaviour and Deposition of Ammonium Nitrate, Nitric Acid and Ammonia

1997 ◽  
pp. 426-432
Author(s):  
Ralph Dlugi ◽  
Lucia Kins ◽  
Thomas Seiler ◽  
Winfried Seidl ◽  
Peter Seifert ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Ammonium Nitrate ◽  
Chemical Behaviour
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