scholarly journals Evidence of nitric acid uptake in warm cirrus anvil clouds during the NASA TC4 campaign

2010 ◽  
Vol 115 ◽  
Author(s):  
Eric Scheuer ◽  
Jack E. Dibb ◽  
Cynthia Twohy ◽  
David C. Rogers ◽  
Andrew J. Heymsfield ◽  
...  
Keyword(s):  
Nitric Acid ◽  
Acid Uptake

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 Supersaturation, dehydration, and denitrification in Arctic cirrus

2005 ◽  
Vol 5 (7) ◽  
pp. 1757-1772 ◽  
Author(s):  
B. Kärcher
Keyword(s):  
Nitric Acid ◽  
Cloud Base ◽  
Acid Uptake ◽  
Ice Crystal ◽  
Air Masses ◽  
Cloud Properties ◽  
Diffusion Limited ◽  
Small Crystals ◽  
Ice Crystal Size ◽  
Efficient Uptake

Abstract. A polar cirrus case study is discussed with the help of a one-dimensional model with explicit aerosol and ice microphysics. It is demonstrated that continuous cooling of air in regions with small amounts of ice and slow ice deposition rates of water vapor drives significant in-cloud supersaturations over ice, with potentially important consequences for heterogeneous halogen activation. Radiatively important cloud properties such as ice crystal size distributions are investigated, showing the presence of high number concentrations of small crystals in the cloud top region at the tropopause, broad but highly variable size spectra in the cloud interior, and mostly large crystals at the cloud base. It is found that weakly forced Arctic cirrostratus are highly efficient at dehydrating upper tropospheric air. Estimating nitric acid uptake in cirrus with an unprecedented treatment of diffusion-limited trapping in growing ice crystals suggests that such clouds could also denitrify upper tropospheric air masses efficiently, but a closer comparison to suitable observations is needed to draw a definite conclusion on this point. It is also shown that low temperatures, high ice supersaturations, and the absence of ice above but close to the cloud top region cause efficient uptake of nitric acid in background aerosol particles.

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.

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