A rough picture about the ground-level ammonia (NH3)

Question

Ammonia is the only alkaline gas in the atmosphere. It is one of the key features to control the acidity of aerosols and the formation of ammonium salts.

In the environment of $NH_3$-rich and $NH_3$-poor, the formation pathway of the secondary aerosol would be distinct.

For example, if $NH_3$ is redundant after the combination with $_2SO_4$, they would continue to react with $HNO_3$ to form $NH_4NO_3$. However, if in the $NH_3$-poor environment, $HNO_3$ would react with the crustal material and thus form nitrate in the coarse mode.

In this way, the concentration levels of $NH_3$ affect the chemical composition, size distribution of atmospheric aerosols.

However, the ground-level monitoring of $NH_3$ is still limited in China with several published ones in limited spots.

Therefore, I want to learn that:

1. Is there any method to estimate NH3 concentration by other species?
2. Is there any dataset (e.g. remote sensing, measurements) offering the distribution of $NH_3$ concentration?

Answer 1

1. It seems difficult to find a reasonable proxy species for $\mathrm{NH}_3$, since its sources (primarily agriculture) are quite distinct from the sources of more commonly observed pollutants. Some observations of aerosol-bound $\mathrm{NH}_4^+$ might (or might not) be available, but due to the reasons you explain, it is non-trivial to infer the gas-phase $\mathrm{NH}_3$ concentration from the $\mathrm{NH}_4^+$ in aerosols.

2. There are papers about estimating atmospheric $\mathrm{NH}_3$ from satellite data, see for example here or here. These are for column-integrated and not surface $\mathrm{NH}_3$, however.

Answer 2

There are some NH3 retrievals available from the TES instrument on the Aura/NASA satellite. There are also some NH3 retrievals from the IASI instrument on the MetOP/ESA satellite. You can read about the retrievals in these papers:

Towards validation of ammonia (NH3) measurements from the IASI satellite

TES ammonia retrieval strategy and global observations of the spatial and seasonal variability of ammonia

These datasets are a good qualitative way to see ammonia spatial and temporal distribution across the globe. However, do not expect to get good estimates of ammonia concentrations, since there is too much uncertainty in the retrieval. In fact, I don't think these are "operational" products, and you will likely have to contact the research teams to get the data. See the image below, where you can see the effects of albedo in Australia and Greenland cause large errors in the retrieval.

In general, you will see high NH3 near large sources like wildfires, livestock waste stockpiling, and crops with recent fertilizer application.

Mean IASI-NH 3 total column distribution for the period between January 2008 and January 2015. The total columns are a weighted average of the individual observations weighted with the relative error. Red circles indicate the positions of the FTIR stations. source: An evaluation of IASI-NH3 with ground-based Fourier transform infrared spectroscopy measurements