Current World Environment

According to recent reports, levels of atmospheric reactive nitrogen species (RNS) are increasing worldwide due to rise in fossil fuel combustion for energy and agricultural yields. The use of fossil fuel is changing air composition by adding NH₃ and NOx  and their related compounds. The other RNS include  HNO₃, HONO, NO₃, N₂O₅, NO₃^- Peroxy acetyl nitrate (PAN), NH₄⁺ etc. The RNS are also disrupting life in general on land and underwater. Some of the RNS are key contributors to climate change. High levels of RNS in water and air affect human health. Also, nitrogen waste management is a great challenge for the economy. It costs between US$340 billion and US$3.4 trillion to global economy after taking into account its effect on human health and ecosystems¹. Food waste also has unnecessary consequences for nitrogen cycle alterations.

Nitrogen dioxide (NO₂) is one of the major RNS and is a criteria air pollutant under National Ambient Air Quality Standards (NAAQS). It is mainly emitted from fossil fuel combustion and biomass burning. It is a precursor to tropospheric ozone. It is oxidized to HNO₃ which is responsible for acid rain. NO₂ is harmful to human health. High levels of NO₂ are linked with acute human respiratory diseases including lung cancer².  Global NO₂ trend is reported increasing from 2005-2018. However, there are regional differences in the trends³. Eastern USA, Western Europe, Japan and for parts of China show some negative NO₂ trends while some parts of China, India and Middle-east show strong positive NO₂ trends.

NH₃ is another criteria air pollutant listed under National Ambient Air Quality Standards (NAAQS). NH₃ is mostly contributed by fertilizers. 81% of global ammonia emissions are from agricultural sources^4-5. Livestock, manure, and synthetic fertilizer application are the major agricultural sources contributing to large fraction of atmospheric NH₃^6-7_. However, a fraction of NH₃ is also contributed by transport sector in urban areas. Ammonia contributes almost 50% of PM_2.5 air pollution in EU and 30% is USA. Ammonium rich PM_2.5 causes chronic respiratory illnesses and can lead to premature mortality.

From Green Revolution to present, the urea consumption in India is increased from 1 million ton to around 33.5 million tons. Higher rates of fertilizer production have caused an increase in RNS. Major fertilizer is urea which is manufactured through Haber-Bosch process during which inert nitrogen (N₂) is transformed into urea. In the urea production process, each molecule of NH₃ production contributes one molecule of CO₂ . Apart from this, transport sector also co-emits NOx and CO₂. Thus, the reactive nitrogen issue is also linked with global warming  and climate change. Also, the application of fertilizer in soil is a source of greenhouse gas (N₂O) responsible for climate change.

Considering the importance of nitrogen pollution, governments adopted a resolution on sustainable nitrogen management at the United Nations Environment Assembly held in 2021. It includes both an ambition to “significantly reduce nitrogen waste globally” as well as a timeline “by 2030 and beyond⁸. Our recent studies have revealed that the reactive nitrogen levels in ambient air are increased significantly⁹. Such pattens need serious attention of scientists and policy makers to monitor selected RNS levels and related impacts, and frame necessary policies on fertilizers and fuels. 

References

1. UNEP. 2018-2019.  Frontiers Report. 2023. https://www.unep.org/resources/frontiers-201819-emerging-issues-environmental-concern. Accessed on December 31, 2023.
2. Hamra, G. B. et al. 2015. Lung cancer and exposure to nitrogen dioxide and traffic: a systematic review and meta-analysis. Environ. Health Perspect. 123, 1107–1112.
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3.  Jamali, S. Klingmyr, D. and Tagesson, T. 2020. Global-Scale Patterns and Trends in Tropospheric NO₂ Concentrations, 2005–2018., 12(21), 3526; https://doi.org/10.3390/rs12213526.
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4. Van Damme, M. et al. 2021. Global, regional and national trends of atmospheric ammonia derived from a decadal (2008-2018) satellite record OPEN ACCESS RECEIVED Global, regional and national trends of atmospheric ammonia derived from a decadal (2008-2018) satellite record Environ. Res. Lett., 16, 10.1088/1748-9326/abd5e0.
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5. Wyer, K. et al. 2022. Ammonia emissions from agriculture and their contribution to fine particulate matter: A review of implications for human health. J Environ. Management, 323. https://www.sciencedirect.com/ science/article/ pii/S0301479722018588.
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6. Behera, S.N.  Sharma, M., Aneja, V.P.  and Balasubramanian, R. 2013. Ammonia in the atmosphere: a review on emission sources, atmospheric chemistry and deposition on terrestrial bodies. Environ. Sci. Pollut. Control Ser., 20 (11), pp. 8092-8131, 10.1007/s11356-013-2051-9.
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7. Sutton, M.A., Reis, S., Riddick, S.N., Dragosits, U.,  Nemitz, E. et al. 2013.Towards a climate-dependent paradigm of ammonia emission and deposition. Phil. Trans. Biol. Sci., 368 (1621), 10.1098/rstb.2013.0166.
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8. UNEP. 2023. Four reasons why the world needs to limit nitrogen pollution. https://www.unep.org/news-and-stories/story/four-reasons-why-world-needs-limit-nitrogen-pollution. Accessed on December 31, 2023.
9. Singh S., Kumar B., Gupta G.P., Kulshrestha U.C. 2014. Signatures of Increasing Energy Demand of Past Two Decades as Captured in Rain Water Composition and Airmass Trajectory Analysis at Delhi (India). Journal of Energy, Environment & Carbon Credits, 2014, 4(3), 43-61.