Earth and Climate Science

Dr Vinayak Sinha
Atmospheric Chemistry and Emissions Research Group, Department of Earth and Environmental Sciences, IISER Mohali

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Abstract: The Earth’s present day oxidizing atmosphere sustains life on Earth by acting as protective shield, a source of nutrient carbon in the form of carbon dioxide for natural forests and food crops and as a chemical modulator of planetary weather and climate. However, when the Earth was first formed about 4.6 billion years ago, the atmosphere lacked oxygen and was reducing in nature. In this talk, I shall start by briefly tracing the history of the Earth’s atmosphere to its present state, highlighting the key biotic, physical and chemical drivers. After the introductory overview, I shall discuss recent research findings made by my research group through new measurement techniques and data concerning the annual phenomenon of agricultural waste burning in the North-West Indo Gangetic Plain (N.W. IGP), which we have been studying in ever increasing detail for the past five years. This practice occurs twice a year, during the months of April-May when wheat stubble is combusted and in October-November when paddy stubble is combusted over an area exceeding 9500 km² of cropland in the N.W. IGP. It has been estimated that about 67 Tg of agricultural residue is burnt annually due to this emission activity in the N.W. IGP alone. The reactive compounds emitted and formed due to such fires drive high ozone and organic aerosol formation episodes in the ambient atmosphere, affecting both air quality and climate. In my talk I shall review what we have learnt by deploying first of their kind mass spectrometric techniques anywhere in India. In particular, by developing and deploying a new instrument capable of directly quantifying the total OH Reactivity of ambient air, a measurement that provides a robust and direct measure of the total reactive pollutant burden and can yield the fraction of unmeasured reactive VOCs in an atmospheric environment by comparison with the calculated OH Reactivity due to the measured OH reactants, I shall show that a very significant fraction of chemically reactive compounds present in ambient air due to the agricultural fires remains unaccounted and so a larger suite of compounds and chemical reactions needs to be incorporated for improved understanding of atmospheric chemistry-air quality-climate feedbacks in similar biomass-fire impacted atmospheric environments around the world.