Ammonia

About: Ammonia is a research topic. Over the lifetime, 16217 publications have been published within this topic receiving 271940 citations. The topic is also known as: NH3 & azane.

Kinetics of NH3-oxidation, NO-turnover, N2O-production and electron flow during oxygen depletion in model bacterial and archaeal ammonia oxidisers

Abstract: Ammonia oxidising bacteria (AOB) are thought to emit more nitrous oxide (N2 O) than ammonia oxidising archaea (AOA), due to their higher N2 O yield under oxic conditions and denitrification in response to oxygen (O2 ) limitation. We determined the kinetics of growth and turnover of nitric oxide (NO) and N2 O at low cell densities of Nitrosomonas europaea (AOB) and Nitrosopumilus maritimus (AOA) during gradual depletion of TAN (NH3 + NH4+) and O2 . Half-saturation constants for O2 and TAN were similar to those determined by others, except for the half-saturation constant for ammonium in N. maritimus (0.2 mM), which is orders of magnitudes higher than previously reported. For both strains, cell-specific rates of NO turnover and N2 O production reached maxima near O2 half-saturation constant concentration (2-10 μM O2 ) and decreased to zero in response to complete O2 -depletion. Modelling of the electron flow in N. europaea demonstrated low electron flow to denitrification (≤1.2% of the total electron flow), even at sub-micromolar O2 concentrations. The results corroborate current understanding of the role of NO in the metabolism of AOA and suggest that denitrification is inconsequential for the energy metabolism of AOB, but possibly important as a route for dissipation of electrons at high ammonium concentration.

Vanadia on sulphated-ZrO2, a promising catalyst for NO abatement with ammonia in alkali containing flue gases

Abstract: Vanadia supported on TiO 2 , ZrO 2 , and sulphated-ZrO 2 have been prepared. These catalysts were characterized by elemental analysis, N 2 -BET, XRD, FTIR, and NH 3 -TPD methods. The stability of surface sulphated groups, studied by FTIR-spectroscopy, was found to depend dramatically on the temperature of the calcination of the samples. No considerable decomposition of surface sulphates was observed below 350 °C. The influence of potassium oxide additives on the acidity and activity in NO SCR with ammonia was studied. It was found that the introduction of small amounts of potassium (K/V molar ratio 2 and ZrO 2 based systems. For the sulphated system, surface sulphur groups, due to their strong acidity, represent attractive sites for the localization of potassium oxide and the decrease in the total acidity is less pronounced in this case. The results of NO SCR with ammonia reveal a noticeable shift of the maximum catalytic activity towards higher temperatures in going from the conventional catalyst to vanadia supported on sulphated zirconia. The loading of the catalysts with potassium leads to considerable decrease of their catalytic activity, and to a shift of the maximum catalytic activity towards lower temperatures. Among all the catalysts, V 2 O 5 /sulphated-ZrO 2 reveals the highest resistance towards alkali poisoning. The presence of SO 2 in the reaction mixture was found to enhance stability and activity of the V 2 O 5 /sulphated-ZrO 2 probably due to regeneration of surface sulphated groups at the reaction conditions. The potassium-doped V 2 O 5 /sulphated-ZrO 2 catalyst reveal high activity and stability at 300 °C, comparable with unpoisoned catalysts. At 400 °C the presence of potassium compounds seems to enhance the deactivation of the catalyst under reaction conditions during 30 h, possibly due to formation of potassium sulphate–pyrosulphate species reacting with vanadium oxide.

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

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.