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

Friday, 19 December 2014
Naveen Chandra Negi1,2, Venkataramani Sethuraman1 and Shyam Lal1, (1)Physical Research Laboratory, Ahmedabad, India, (2)Indian Institute of Technology Gandhinagar, Physics, Ahmedabad, India
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 (23.03oN, 72.58oE, 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.