Simultaneous measurements of CO2, CO and CH4 at an urban site of western India using cavity ring down spectroscopy (CRDS) technique.

Abstract:

The atmospheric levels of CO₂ and CH₄ are mainly governed by emissions from several anthropogenic as well as biogenic sources. Anthropogenic sources have different emission characteristics, and emit CO₂, CH₄ with various other trace gases like CO, NOx, SO₂... etc in different ratios. CO is a useful tracer for differentiating between natural and anthropogenic emissions, as the natural source does not affect its levels significantly. Therefore the interrelations of CO2, CH4 with CO and other co-emitted species can be useful for identifying the relative role of emission sectors on the total emission of CO₂ and CH₄. Simultaneous measurements of CO₂, CO and CH₄ were made over Ahmedabad (23.03^oN, 72.58^oE, 55m AMSL), a semi-arid urban site of western India, during the period of autumn (November 2013), winter (December 2013–February 2014) and Monsoon (July 2014) using an online analyser based on the cavity ring-down spectroscopy technique. The measurements show that atmospheric CO correlates well with CO₂ during the autumn and winter. The slope of CO and CO₂ (∆CO/∆CO₂) is found to be in the range of 0.02 and 0.03 which agrees well with the emission ratio for India as per Asian inventory proposed by Street et al., (2003) and connote the influence of mixed sources (fossil fuel as well as biomass burning) during this period. In July , CO doesn’t correlate well with CO₂ (r² =0.14), but the slope is around 0.005, indicates the dominance of fossil fuel during this time. The correlation and slope (slope ~ 0.02 and r² ~ 0.55) of CH₄ with CO₂ remain fairly constant which demonstrate that the study area does not have significant changes in the source of these gases throughout the study period. Details of the levels, amplitude of diurnal variations of CO₂, CO, CH₄ as well as their mutual interrelationship will be presented.