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Inhale, exhale: Patterns in atmospheric Carbon Dioxide

Every evening, a blanket of pollution binds carbon dioxide close to the surface of the Earth, which lasts through the night. There was also more carbon dioxide build up during the summer, rather than during the monsoons. These findings came to light in a recently published long-term study by the Indian Institute of Science (IISc), which has mapped variations in carbon dioxide content in the atmosphere,at different time scales as measured from Bangalore. The results only reinforce the complexities of our atmosphere.

At the end of this month, we will have a verdict from the International Commission of Stratigraphy (ICS). Has the time come to welcome a new geological era for the Earth’s future, the Anthropocene? The epoch of major, ongoing impacts of human life on planet Earth. Although we might have a global consensus on the real threat of climate change, we are still groping in the dark for solutions. A recent study from the Indian Institute of Science, Bangalore has shown just how difficult it is to find global trends in an atmosphere that is so dynamic even at a local scale.

Prosenjit Ghosh from the Centre for Earth Sciences as well as Centre for Atmospheric and Oceanic Sciences and Tania Guha from the Centre for Earth Sciences, both at IISc, conducted a three year study from 2008-2011 where they measured carbon dioxide (CO2) content in the atmosphere over Bangalore, and also quantified its different isotopes or ‘types’. Day to day CO2 levels varied in a manner that depended heavily on where the measurement was taken.

“Urban sites are hot-spots for CO2 emission - however, seasonal transport and mixing of air from marine locations also control the concentration of urban CO2,” said Dr. Ghosh. “Our interest was to capture such variability in our observations and comment on the origin of CO2 molecules.”

The team obtained data at two timescales: monthly data, by averaging measurements for 4-5 days of a month and daily estimates, by taking measurements twice daily on alternate days. Three years of consolidated numbers derived from two different methods, later the study had some fascinating things to offer . Early morning carbon dioxide was higher than late evening amounts, backing the theory proposed by the authors that a ‘blanket’ of pollution binds the CO2 close the surface of the Earth at night. There was significant monthly variability, perhaps arising from the varying heights of this ‘blanket’ at night. 

The different types of Carbon

Not all atoms of an element are identical; some have extra or fewer neutrons than their cousins. The collection of these ‘cousins’ with marginal differences in properties are known as isotopes. Carbon is one such family – Carbon-12 and Carbon-13 are the two most abundant (and stable) isotopes, though Carbon-13 is 100 times rarer than its cousin. Most plants preferentially absorb Carbon-12; so, an increase or decrease in green cover can be measured by an increase or decrease in Carbon-13. Alternatively, a reduction in green cover releases this previously absorbed Carbon-13, thereby diluting the proportion of Carbon-13.

Retracing the atmospheric CO2 to its sources can be tricky, with existing models not accounting for many major local effects. For instance, the monsoon winds wash over the local cycles in CO2 absorption and generation, and limestone quarries are an important source of the carbon with high carbon-13 signatures. Burning of biomass and fossil fuels were the two major sources of CO2, and a clear peak in CO2 levels was seen during the higher summer months, followed by reduced levels during the monsoon months from June to September.

The expansion of agriculture and natural vegetation explains this, and this is further corroborated by trends in the proportion of Carbon -13 (see box). This seasonal trend did not apply, however, to 2011 – a La Nina year. La Nina is a climate phenomenon with global implications. In the subcontinent, it brings with it above average and sporadic rainfall. Early rains in 2011 markedly reduced forest fires in nearby forests so the rise in CO2 levels in the summer of 2011 was significantly lower.

More studies will definitely reveal information that will help manage climate change, but that is easier said than done, as Dr. Ghosh explains. “The cost of equipment including the setup designed here is nearly 400,000 Euros (or Rs. 3 Crores!), which is (the) minimum requirement to setup such a facility. There are limited resources in this country to generate interests on air quality and atmospheric chemistry. It is taught at rudimentary stages in our universities and colleges.”

But the challenge isn’t unsurmountable. As Dr. Ghosh goes on to explain, solutions to work around these obstacles already exist - “The IPCC provided a major impetus in making these subjects socially relevant”, he said. “We are organizing routine workshops and courses for the student at Devicha Centre for Climate Change, IISc with whom I am closely associated.With more investment, we will be in a position to provide real time data on air quality to our citizens and policy makers.”

About the authors

Prosenjit Ghosh is an Associate Professor with the Centre for Earth Sciences and the Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, Bangalore.

Contact: Phone 080-22932599; ghoshceas@gmail.com

Website: http://caos.iisc.ernet.in/faculty/pghosh/pghosh.html

The paper appeared in the journal Environmental Science and Pollution Research on 9th October. http://link.springer.com/article/10.1007%2Fs11356-014-3530-3