Diurnal and seasonal variability of CO2 and CH4 concentration in a semi-urban environment of western India

Abstract

Amongst all the anthropogenically produced greenhouse gases (GHGs), carbon dioxide (CO₂) and methane (CH₄) are the most important, owing to their maximum contribution to the net radiative forcing of the Earth. India is undergoing rapid economic development, where fossil fuel emissions have increased drastically in the last three decades. Apart from the anthropogenic activities, the GHGs dynamics in India are governed by the biospheric process and monsoon circulation; however, these aspects are not well addressed yet. Towards this, we have measured CO₂ and CH₄ concentration at Sinhagad, located on the Western Ghats in peninsular India. The average concentrations of CO₂ and CH₄ observed during the study period are 406.05 ± 6.36 and 1.97 ± 0.07 ppm (µ ± 1σ), respectively. They also exhibit significant seasonal variabilities at this site. CH₄ (CO₂) attains its minimum concentration during monsoon (post-monsoon), whereas CO₂ (CH₄) reaches its maximum concentration during pre-monsoon (post-monsoon). CO₂ poses significant diurnal variations in monsoon and post-monsoon. However, CH₄ exhibits a dual-peak like pattern in pre-monsoon. The study suggests that the GHG dynamics in the western region of India are significantly influenced by monsoon circulation, especially during the summer season.

Figure 1

The outgoing longwave radiation on a monthly scale (shaded) at the surface (1000 mb) during (a) July (average of 2014–2015) and (b) January (2015). Arrows indicate wind vectors. A blue rectangle marks station Sinhagad. The wind rose diagram for (c) CO₂ and (d) CH₄ are also shown.

Figure 2

Seasonal variation of (a) CO₂ and (c) CH₄ at Sinhagad, for the year 2014–2015. The shaded region shows the standard deviation. Seasonal variations of other sites are also shown in the figure. N.B-Seasonal variation of knp is obtained in the year 2016, but it is shown in 2015 in the graph for comparison purpose only. Similarly, cri seasonality is obtained from monthly mean data of 2010–2012 but shown in 2015 in the graph for comparison only. Highlighted markers in sng time series in May and June, 2015 is obtained from weekly flask samples to fill the gap. Seasonal amplitude (maximum − minimum) of several sites is shown in (b) for CO₂ and in (d) for CH₄.

Figure 3

(a–d) 10-day back trajectories arriving at Sinhagad at a surface level during monsoon, post-monsoon, winter, and pre-monsoon.

Figure 4

(a) Co-variance of CO₂ and NDVI calculated over an area of 0.5° × 0.5° for the entire observation period. (b) Co-variation of CH₄, NDVI, and CH₄ flux from agriculture and waste of CT-product. N.B-The highlighted points in CO₂ and CH₄ time series denotes data from weekly flask samples.

Figure 5

Biplot in PC1 and PC2 space showing the association of individual variables and their phase relationship for (a) monsoon (July–August–September), (b) post-monsoon (October–November), (c) winter (December–January–February), and (d) pre-monsoon (March–April–May).

Figure 6

Diurnal variation of seasonal CO₂, CH_4, and planetary boundary layer height (PBL) during (a) monsoon, (b) post-monsoon, (c) winter, and (d) pre-monsoon.