Current World Environment

Dear Readers

The present issue of the Current World Environment is presented before you. I thank the authors, reviewers and the journal secretariat for timely publishing the issue. This issue includes research papers from diversified subareas of environment as given in the table of content. This time we have included `Editorial Contributions’ from our Editorial Board members. The theme of the Editorial of this issue is Reactive Nitrogen as detailed below-

The food and energy demand of the global population has resulted in the rapid increase in the levels of reactive nitrogen species (Nr) such as NH₃, NOx, NO₃^- and NH₄⁺ etc. in the atmosphere across the globe. These compounds affect air quality, human health, climate, ozone levels, etc. NO₂ at high levels may be responsible for almost 2 million deaths per year due its indoor pollution effect¹. NO₂ forms smog with excessive O₃ and organic compounds such as aldehydes, ketones and peroxyacyl nitrate (PAN) etc. The excess concentrations of the nitrogenous compounds have adverse impacts on water bodies causing eutrofication problem. Nr species are contributed by both natural as well as anthropogenic activities. Apart from natural sources, anthropogenic sources such as fertilizer production, fertilizer application, fossil fuel combustion and sanitation etc. are the major contributors of the Nr species. A comprehensive Nitrogen Assessment for India has been published by Abrol and co-workers.²

Recent research highlights that the anthropogenic N fixation from biological nitrogen fixation (BNF), fertilizers and combustion is estimated as 220 Mt per year against 65 Mt as the natural N fixation from BNF and lightning.³ This indicates that the extent of human perturbation in N cycle.⁴ After north America and Europe, Asian region has the third highest N deposition rates.⁵ The global anthropogenic Nr budgets have been calculated by Dentener et al., using a multi-model approach.⁶ Indian consumption of nitrogenous fertilizer has touched 15 million tons in 2010-11 against 1 million ton in 1960s.⁷ Indo-Gangetic region is considered as a hot spot of Nr abundance.⁸-⁹ In India, among N-NH₃, N-NH₄ and N-NO₃ species, gaseous ammonia contributes highest N in the air.¹⁰ Megacities are huge contributors to the reactive nitrogen. NO₂ levels are seen growing due to their emissions from fossil fuel combustion in thermal power plants, industries and automobiles etc.¹¹ NO2 is a significant contributor to the poor air quality of Delhi and other megacities. NO₂ and NO₃^- are also responsible for acid rain.¹² The number of vehicles and population in all the mega cities has risen exponentially. Probably, due to this reason, a remarkable increase in NH₄ and NO₃ fluxes has been reported at Delhi since 1994.¹³

In the agriculture, most of the NH₃ is emitted during fertilizing stage. The urea which is a major fertilizer is the main source of higher NH₃ during fertilizing stage. Urea (NH₂CONH₂) on dissociation results in NH₃ emission. Higher temperature and alkaline dust aerosols adds to the dominance of NH₃ in gaseous phase in contrast with the acidified regions.¹⁴ The ratio of NH₃/NH₄ remains higher in Indian region (alkaline aerosols) as compared to the acidified regions (acidic aerosols). There is a need to carry out studies on NH₃ emissions during different stages of agriculture which can be of help in efficient N management. Similarly, agriculture activity has been considered a major source of N₂O. Paddy cultivation is one among major contributors of N₂O emissions.¹⁵ Livestock is another sector responsible for Nr contributions. N₂O emissions and annual growth rates from different livestock categories have been reported by Aneja et al.,¹⁶ However, the large discrepancies in the Nr budget from livestocks need to be reduced.

The Nr species are deposited through wet and dry deposition processes. The coarser particles are deposited through dustfall which is very common in dusty regions.¹⁷ Wet deposition of Nr species has been reported more extensively as compared to the dry deposition of Nr species.¹⁸ Sensitive ecosystems such as Himalayan region and Western Ghats are highly affected by the deposition of NO₃ and NH₄.^19-20 Deposition of NO₃ and NH₄ contributed by both local as well as transported sources has been reported by Kumar et al.,²¹ Emission vs deposition budgets of major Nr species have been given by Kulshrestha.¹⁰

Recently, carbon cycle imbalance has been the focus of scientific community as well as policy makers. Global warming and climate change issues related research has added tremendous new knowledge about the sources, phases, chemical and physical characteristics of carbonaceous aerosols. Before it becomes second carbon, reactive nitrogen issue needs attention. There is great need to review our fertilizer and fuel policies now. A detailed overview of the south Asian scenario of reactive nitrogen and the suggested actions has been given by Naseem and Kulshrestha.²² It is worth mentioning here that under the UK Global Challenge Research Fund, the `GCRF South Asian Nitrogen Hub (SANH)’ project has been started which has 32 leading research organizations as partners. SANH is a mega project having all eight south Asian countries and the South Asia Co-operative Environment Programme (SACEP). There are several gaps in the nitrogen increase estimatesand its impact assessment but hopefully, this SANH project will be able to provide suitable solutions which can help in effective global nitrogen management.

References

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2. Abrol, Y. P., Adhya, T. K., Aneja, V. P., Raghuram, N., Pathak, H., Kulshrestha, U., Sharma C. Singh, B. (Eds.). (2017). The Indian Nitrogen Assessment: Sources of Reactive Nitrogen, Environmental and Climate Effects, Management Options, and Policies. Elsevier. ISBN: 978-0-12-811836-8.
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