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1. How is ammonia emission potential calculated using IASI satellite data?

2. What is the correlation between IASI ammonia measurements and ground-based ammonia measurements?

3. What is the resolution of the MERRA-2 reanalysis product used in the GEOS-Chem model?

4. Why choose EC-Earth climate model?

Accepted Answer

Ammonia emission potential is calculated using IASI satellite data by measuring the total column concentration of ammonia (molecules cm-2) and soil temperature at the surface. The equation used is Eq. (2-1) or Eq.(A-15) in Appendix A: soil = [NH 3 ] col . T soil exp ( -b T soil ) M NH 3 a . N a . c' . 1 k (2-1). This calculation considers the dissolution of ammonia in soil water following Henry's law and assumes equal emission and loss in steady state conditions. The soil atmosephere exchange coefficient (deposition velocity) affects the calculation and is influenced by factors such as surface roughness, wind speed, boundary layer height, and pH. Look up tables provide values for different land cover types and seasons based on a resistance model. The mass transfer coefficient ranges from 10^-3 to 10^-2 m/s in soil and manure mixtures, and 10^-6 to 10^-5 m/s in manure alone. The full derivation of the equation is explained in Appendix A.

Accepted Answer

Recent studies have shown a good correlation between IASI ammonia measurements and ground-based ammonia measurements. A study by Viatte et al. (2021) found a correlation coefficient (R) of 0.75, indicating a strong relationship between the two datasets. This correlation was observed when comparing ammonia measurements from the Infrared Atmospheric Sounding Interferometer (IASI) with those from a ground-based instrument. The consistency of results between satellite and ground-based measurements is crucial for validating the accuracy of ammonia retrievals from IASI and ensuring reliable data for further research and analysis.

Accepted Answer

The MERRA-2 reanalysis product used in the GEOS-Chem model has a resolution of 2deg x 2.5deg. This product is the second version of the MERRA atmospheric reanalysis product by NASA Global Modulation Assimilation Office (NASA/GMAO) (Gelaro et al., 2017). The MERRA-2 reanalysis product is driven by the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) reanalysis product, which is used as boundary conditions for the nested domains over Europe at a 0.5deg x 0.625deg horizontal resolution. The global simulation for the nested domains is created using a resolution of 2deg x 2.5deg. The model output for March of 2011 includes the monthly mean for selected diagnostics, and anthropogenic emissions are taken primarily from the global Community Emissions Data System (CEDS) inventory (Hoesly et al., 2018). Biogenic non-agricultural ammonia, as well as ocean ammonia sources, are taken from the Global Emission Inventories Activities database (GEIA, Bouwman et al., 1997). Open fire emissions are generated using the GFED 4.1s inventory (Randerson et al., 2015). The ammonia emissions over Europe are obtained using the Harmonized Emissions Component module (HEMCO) (Keller et al., 2014).

Accepted Answer

The EC-Earth climate model is chosen due to its compatibility with the ammonia product from IASI, which uses ERA5 for retrievals. It calculates emission potential from the T skin product of ERA5. The model uses the ECMWF Integrated Forecasting System for the atmosphere-land component (IFS), complemented with other model components to simulate Earth system interactions. However, the versions of IFS models used in ERA5 and EC-Earth are not identical, as the climate model product is not assimilated and is not initialized with observations. The model is used for future projections under different shared socio-economic pathways (SSP) from 2015 to 2100, analyzing two scenarios: SSP2-4.5 and SSP5-8.5.

Accepted Answer

The GEOS-Chem model simulates atmospheric ammonia by analyzing monthly averaged ammonia total columns output. It compares these outputs to IASI total columns gridded on the same horizontal resolution and over the same month. The model shows coincident sources of ammonia, reflecting its ability to reproduce ammonia columns over major agricultural source regions in Europe. However, GEOS-Chem underestimates ammonia columns by up to 2 x 10^16 molecules/cm2 in some source regions, especially in England, North Eastern France, the North European Plain, and Spain. The differences in the model's simulation are mainly due to the time coincidence and the fact that only cloud-free data are used to retrieve ammonia. The model's MRD values vary across different regions, with the Po Valley in Italy having the highest MRD value (+110%) and New Aquitaine in the southwest of France having the lowest (-20%). Despite the bias and MRD, the spatial distribution between IASI and GEOS-Chem is consistent, indicating that the meteorological and soil parameters affecting one dataset are applicable to the other.

Accepted Answer

The dominant ammonia loss mechanisms in agricultural source regions in Europe during March 2011 are chemical reactions, wet deposition, and dry deposition. Chemical reactions, such as the transformation of ammonia into inorganic particulate matter, account for more than 50% of the total ammonia loss pathways in most regions. Wet deposition and dry deposition also contribute to the loss of ammonia, with wet deposition accounting for 1 to 5% of the total loss. Additionally, transport mechanisms play a role in ammonia loss, with 30% to 34% of the total sinks in regions neighboring the Atlantic Ocean.

Accepted Answer

Ammonia emission potential in Europe varies based on source regions such as the North European Plain, Brittany, and the Po valley. The GEOS-Chem chemistry transport model accurately reproduces key spatio-temporal patterns of ammonia levels. Emission potentials range from 2 x 10^3 to 9.5 x 10^4 in fertilized lands (croplands). The increase in T skin temperature affects ammonia emission from the soil. Ammonia columns are expected to double under the SSP5-8.5 scenario and increase by up to 50% under the SSP2-4.5 scenario. The eastern part of Europe, including Italy, Spain, Belgium, and the Netherlands, experiences the highest increase in ammonia columns. Future research should focus on ammonia emission potential in different seasons and land use types, as well as daily emission potentials to understand diurnal variability. The launch of the IRS on MTG satellites in 2025 will aid in obtaining ammonia columns at different times of the day.

Accepted Answer

Henry's equilibrium describes the relationship between the concentration of ammonia gas in the air and its dissolved form in water. When ammonia gas dissolves in water, it follows Henry's law, which states that the concentration of dissolved ammonia is directly proportional to the partial pressure of ammonia gas above the solution. The equilibrium can be expressed mathematically as: [NH3] = kH * PNH3, where [NH3] is the concentration of dissolved ammonia, kH is Henry's law constant, and PNH3 is the partial pressure of ammonia gas. In the case of ammonia, the Henry's law constant is 2.75 x 10^-3 mol/(L·atm). This constant is influenced by factors such as temperature and the presence of other solutes in the solution. Understanding Henry's equilibrium is crucial for predicting the behavior of ammonia in various environmental and industrial processes.

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Most frequently asked questions

1. How is ammonia emission potential calculated using IASI satellite data?

2. What is the correlation between IASI ammonia measurements and ground-based ammonia measurements?

3. What is the resolution of the MERRA-2 reanalysis product used in the GEOS-Chem model?

4. Why choose EC-Earth climate model?

5. How does GEOS-Chem model simulate atmospheric ammonia?

6. What are the dominant ammonia loss mechanisms in agricultural source regions in Europe during March 2011?

7. How does ammonia emission potential vary in Europe?

8. What is Henry's equilibrium in relation to ammonia dissolution?

References

The ERA5 global reanalysis

Overview of the Coupled Model Intercomparison Project Phase 6 (CMIP6) experimental design and organization

The Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2)

The Shared Socioeconomic Pathways and their energy, land use, and greenhouse gas emissions implications: An overview

Global modeling of tropospheric chemistry with assimilated meteorology : Model description and evaluation

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