Spatio-temporal variability of CO over the Eastern Indo-Gangetic Plain (IGP) and in parts of South-East Asia: a MERRA-2-based study

The present study revolves around the distribution of surface CO concentrations around the industrial belts of the Eastern Indo-Gangetic Plains (IGP) and in parts of Southeast Asia over a period of 10 years from January 2007 to December 2016. MERRA-2 reanalysis fields are analysed to study the long-term spatial and seasonal behaviour of CO. The focus is on three CO hotspot areas in this region, denoted by A, B and C, which are further subdivided into eight smaller divisions based on topographical and regional characteristics as discussed in details in “Study Region & Meteorology” section. The monthly average distribution of CO in all the eight zones ranges from 750 (C1) to 3781(A2) ppbv. Very high values are consistently observed in the Indo-Gangetic Plains as compared with other regions during the entire period of study. Seasonal variation of surface CO concentration indicates high values in the post-monsoon or winter season. Analysis of spatio-temporal variation alongside emission, chemical production and loss reveals that presence of surface CO is predominantly due to combustion of fossil fuels and burning of organic matters. Fire hotspot data from FIRMS also support these results. Statistical analysis performed using the non-linear regression model further elucidates the sources of CO in the hotspot areas. The coefficient of determination (R2) values between surface CO concentration (response variable) and emission, chemical production and loss (the independent process variables) for all the zones show interesting results. MERRA-2 does not consider any kind of convective transport as influx and outflux of the hypothetical control volume (box) and as such slightly overestimates the net CO concentration as compared with the ground-based measurements under steady-state scenarios.