An Overview of Atmospheric Reactive Nitrogen Research: South Asian Perspective

Abstract

The unprecedented increase in Nr is causing several environmental problems such as eutrophication, ozone depletion and climate change etc. Excessive Nr creation is also responsible for poor plant and human health, soil acidification, groundwater contamination etc. Inhabiting ~ one-fourth population of the world and sharing only 4.9% of land of the total global landmass, the South Asian region consumes 60% of the total global fertilizer nutrient. India is the largest consumer of synthetically produced fertilizer in South Asia. According to estimates, India consumes ~ 17 million tonnes Nr/yr, making South Asia and India a hot spot for the deposition of N species. In India, the fertilizer N consumption is increased 314 folds from 1950-51 to 2013-14. In 1951-52 per hectare fertilizer N consumption was 0.44 kgha-1 while it was 86.2 kgha-1 in 2013-14. Since rains are limited to a few months, most of the time the weather is hot and dry. And hence, the dry deposition is the key mechanism of pollutant removal in the region. Wet deposition predominantly occurs during the monsoon period. The wet deposition of NH3-N observed to be the highest in the Indo-Gangetic plains. The annual NO3-N deposition at the urban, suburban, rural and industrial site found to be 4.48, 2.10, 4.06 and 3.92 kgha-1 respectively, and the annual deposition of NH4-N at the urban, suburban, rural and industrial site found to be 2.38, 2.10, 2.38 and 5.05 kgha-1 respectively. The average total wet deposition of NO3-N and NH4-N in India is estimated to be 6.01kgha-1 which is equivalent to 1.97 Tg N/yr. The average total dry deposition of NH4-N and NO3-N through dust fall found to be 0.37 kg ha-1 and 0.84 kg ha-1 respectively. The average total dry deposition of NH4-N and NO3-N in the form of aerosols found to be 0.28 and 1.65 kg ha-1 while through gaseous dry deposition it was 4.72 kg ha-1 and 0.28 kg ha-1 for NH4-N and NO3-N respectively. This study highlights the need for integrated nitrogen monitoring and assessment in South Asia.