Local emission and long-range transport impacts on the CO, CO2, and CH4 concentrations at a tropical rural site.

Local emission and long-range transport impacts on the observed concentrations (dry air mole fractions) of CO, CO 2 , and CH 4 have been investigated using three years (April 2016 to April 2019) of surface measurements at a tropical rural site, Gadanki (13.5° N, 79.2° E) in Southern peninsular India. Gadanki represents the poor coverage area of Greenhouse Gas (GHG) measurements in India and has both local emission and long-range transport influences on its air masses. All the three gases have shown strong seasonality and diurnal variations. Trend analysis showed a significant decreasing trend in CO (14.3 ± 0.2 ppbv/year) and increasing trends in CO 2 (2.5 ± 1.2 ppmv/year) and CH 4 (11.1 ± 0.03 ppbv/year). CO 2 and CH 4 trends are marginally higher than the global trends (2.2 ± 0.004 ppmv/year and 7.0 ± 0.001 ppbv/year, respectively) for the same period highlighting the sustained local emission impact on the observed concentrations. Among the three species, CO has been the most local emission impacted species with local emission contribution (to the total observed concentration) varying between 4 and 25% during different seasons with a median value always lying above 10% irrespective of the season. In the case of CO 2 and CH 4 , the local emission contribution found to vary in the range of 0.8–7% and 0.15–3%, respectively. Long-range transport impact dominance over the local emission is observed in CO 2 and CH 4 during all the seasons. Analysis using MODIS fire count data, Concentration Weighted Trajectory (CWT) and FLEXPART have reconfirmed the combined effect of local and long-range transport impacts on the observed concentrations. Comparison of the IASI MetOp and AIRS satellite data products with surface measurements showed the significant bias and poor representation of the seasonality demonstrating the limitations on the sensitivity of satellite trace gas measurements within the boundary layer. [Display omitted] • Local emission and long-range transport impacts on CO, CO 2 , and CH 4 have been investigated at a tropical rural site. • CO has been the most local emission impacted species among the three. • Forest fires, agricultural residue and biomass burning have been the dominant local sources. • Trend analysis showed a significant decreasing trend in CO and increasing trends in CO 2 and CH 4. • Comparison of satellite data with surface measurements showed a significant difference. [ABSTRACT FROM AUTHOR]