Satellite Monitoring of Ammonia: Main Achievements and Promising Perspectives

Martin Van Damme 
Université libre de Bruxelles (ULB), Spectroscopy, Quantum Chemistry and Atmospheric Remote Sensing (SQUARES), Brussels, Belgium, and Royal Belgian Institute for Space Aeronomy, Brussels, Belgium

Lieven Clarisse 
Université libre de Bruxelles (ULB), Spectroscopy, Quantum Chemistry and Atmospheric Remote Sensing (SQUARES), Brussels, Belgium

Pierre Coheur
Université libre de Bruxelles (ULB), Spectroscopy, Quantum Chemistry and Atmospheric Remote Sensing (SQUARES), Brussels, Belgium

Winning article: Global, regional and national trends of atmospheric ammonia derived from a decadal (2008–2018) satellite record (Environmental Research Letters, 2021)

“Global ammonia monitoring has a significant role in addressing crucial issues of pollution, biodiversity, food security and climate change”

Our research at the atmospheric spectroscopy group at the SQUARES laboratory (“Université libre de Bruxelles”, Brussels, Belgium) is centred around the monitoring of the chemical composition of the Earth’s atmosphere from satellites. We primarily rely on measurements made by space instruments operating in the infrared domain, with the Infrared Atmospheric Sounding Interferometer (IASI) (on Metop European satellites) being a pioneer. In 2009, our publication in Nature Geoscience (Clarisse et al., 2009) made a significant breakthrough in showing the first global mapping of ammonia (NH3). NH3 together with the nitrogen oxides are the main reactive nitrogen (Nr) species. NH3 is mainly emitted by agricultural activities. Other sources include biomass burning, waste, road transport and industries (Van Damme et al., 2018). Atmospheric Nr emissions have increased fivefold since preindustrial times (Fowler et al., 2013). Upon deposition in ecosystems, reactive nitrogen threatens biodiversity and reduces soil and water quality (Guthrie et al., 2018; Sutton et al., 2011). In Europe, 62 % of ecosystems are exposed to excess levels of nitrogen and the projections for the next decade show little improvement, with 58 % of the Natura 2000 protected areas at risk in 2030 (EEA, 2019). NH3 is also a key precursor of atmospheric secondary particulate matter (PM2.5) (Seinfeld and Pandis, 2016), fine inhalable particles, and is therefore a critical air pollutant. PM2.5 are responsible for millions of premature deaths per year worldwide (Lelieveld et al., 2015).

The 2009 space-observed map of NH3 revolutionized the way nitrogen pollution can be monitored and opened new avenues for studying the flows of reactive nitrogen and their impacts. Before that, NH3 was mainly monitored by sparse surface monitoring networks of limited use for studying the cycle of Nr on representative scales. NH3 has a short atmospheric lifetime, which in turn leads to very large variations of its concentration in space and time. The limitation of the global in-situ monitoring system for NH3, which is obviously a major obstacle to evaluate the impact of planned or implemented policies for air quality management, has therefore been progressively alleviated with the availability of global satellite measurements.

Figure 1: (a) Catalogue of NH3 point sources overlaid on the averaged NH3 total column map (2008-2022). (b) NH3 trends (yearly total relative to 2008) reported by IASI (2008 – 2022) for selected countries, EU-28 and the entire world. (c) Distribution of the absolute national trends over the same period. Relative trend values (in %) have also been indicated for selected countries. (source: ULB, updated from Van Damme et al., 2018, Clarisse et al., 2019b and Van Damme et al., 2021).

Ten years after the first global NH3 distribution, with the accumulation of satellite measurements and improvement in processing tools, a new mapping at 1 km resolution was achieved, dramatically improving the identification of NH3 point sources on a global scale (Van Damme et al., 2018, Clarisse et al., 2019a). It also highlighted that the emission fluxes of super-emitters, from agriculture and industry, were vastly underestimated in current inventories. The first satellite-based catalogue of NH3 regional and point sources was released, which has been continuously updated in recent years (Clarisse et al., 2019b, World Emission, 2024). It now holds over 600-point sources that have been identified, categorized and quantified (Figure 1a).

From the satellite perspective, a new advancement was made in Van Damme et al. (2022) who obtained the first trends in atmospheric NH3 concentrations over ten years, at national, continental, and global scales. It was based on a decadal record (2008-2018) of IASI satellite measurements. While NO2 concentrations have been declining steadily over the past decades (Elguindi et al., 2020), we have shown that this is not the case for NH3. Over these 11 years, a worldwide increase of 12.8 ± 1.3 % over land was indeed found, mainly driven by East Asia, which stands out with the largest trend of 5.80 ± 0.61 % per year. The reported national trends show however large disparities between countries. The upward trends are, in most cases, attributed to a combination of increasing emissions and a longer lifetime of NH3 in the atmosphere, due to declining emissions of sulfur and nitrogen oxides (Figures 1b and 1c).

Despite the success made by hyperspectral infrared sounders in polar orbit, their scientific impact has been limited by (1) their relatively coarse spatial resolution (12-25 km) and (2) their fixed overpass time (twice per day, once during day and once during night). A lot is to be expected from upcoming geostationary missions, which provide NH3 measurements at a much higher temporal sampling. These will be a game changer for NH3 monitoring. A first demonstration of this was made by the group (see Clarisse et al. (2021)) using measurements from the Geostationary Interferometric InfraRed Sounder (GIIRS), which revealed intra-day variabilities over East Asia. Geostationary observations of NH3 will also soon come over Europe by the InfraRed Sounder (IRS) instrument onboard MTG-S from 2025 onwards. IRS will provide a continental mapping without gaps every 30 min, at a spatial resolution of 6 km.

More broadly, the results summarized above underscore the essential role of global NH3 monitoring in addressing urgent issues related to the cascading effects of nitrogen pollution, including decreased life expectancy due to poor air quality, loss of biodiversity linked to excessive nitrogen deposition in ecosystems, and climate change. Satellite observations of NH3 will be key to monitor atmospheric changes due to anthropogenic nitrogen perturbations, especially in view of the foreseen use of NH3 as energy source and long-distance energy carrier (as intermediate storage of hydrogen). They will also support national and international initiatives aiming at bringing nitrogen flows within planetary boundaries while maintaining the safety and food security of the global population, which remains one of the greatest challenges of the 21st century.

Photo 1: Pierre Coheur, Martin Van Damme and Lieven Clarisse surrounding a replica of the IASI-NG satellite instrument.

References

1. Clarisse, L., Clerbaux, C., Dentener, F., Hurtmans, D. and Coheur, P.F.: Global ammonia distribution derived from infrared satellite observations. Nat. Geosci. 2(7), 479–483, 2009.

2. Clarisse, L., Van Damme, M., Gardner, W. et al. Atmospheric ammonia (NH3) emanations from Lake Natron’s saline mudflats, Sci. Rep., 9, 4441, 2019.

3. Clarisse, L., Van Damme, M., Clerbaux, C. and Coheur, P.F.: Tracking down global NH3 point sources with wind-adjusted superresolution. Atmos. Meas. Tech., 12, 5457-5473, 2019b.

4. Clarisse, L., Van Damme, M., Hurtmans, D., Franco, B., Clerbaux, C., & Coheur, P.-F.: The diel cycle of NH3 observed from the FY-4A Geostationary Interferometric Infrared Sounder (GIIRS). Geophys. Research Letters, 48, e2021GL093010, 2021.

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9. Seinfeld and Pandis, Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, 3rd Edition, J. Wiley & Son, 2016.

10. Van Damme, M., Clarisse, L., Whitburn, S., Hadji-Lazaro, J., Hurtmans, D., Clerbaux, C., Coheur, P.-F.: Industrial and agricultural ammonia point sources exposed, Nature, 564, 99–103, 2018.

11. Van Damme, M., Clarisse, L., Franco, B., Sutton, M.A., Erisman, J.W., Wichink Kruit, R., Van Zanten, M., Whitburn, S., Hadji-Lazaro, J., Hurtmans, D., Clerbaux, C., Coheur, P.-F.: Global, regional and national trends of atmospheric ammonia derived from a decadal (2008–2018) satellite record, Environ. Res. Lett., 16, 055017, 2021.

12. World Emission, ESA project, https://www.world-emission.com/ (last access: 20/02/2024).