Observational Evidence of Large Contribution from Primary Sources for Carbon Monoxide in the South Asian Outflow

Abstract

South Asian air is among the most polluted in the world, causing premature death of millions and asserting a strong perturbation of the regional climate. A central component is carbon monoxide (CO), which is a key modulator of the oxidizing capacity of the atmosphere and a potent indirect greenhouse gas. While CO concentrations are declining elsewhere, South Asia exhibits an increasing trend for unresolved reasons. In this paper, we use dual-isotope (δ 13 C and δ 18 O) fingerprinting of CO intercepted in the South Asian outflow to constrain the relative contributions from primary and secondary CO sources. Results show that combustion-derived primary sources dominate the wintertime continental CO fingerprint ( f primary ∼ 79 ± 4%), significantly higher than the global estimate ( f primary ∼ 55 ± 5%). Satellite-based inventory estimates match isotope-constrained f primary -CO, suggesting observational convergence in source characterization and a prospect for model–observation reconciliation. This “ground-truthing” emphasizes the pressing need to mitigate incomplete combustion activities for climate/air quality benefits in South Asia.

Retrospective Isotopic Analysis of Summertime Urban Atmospheric Sulfate in South Asia Using Improved Source Constraints

“…It is recognized that in order to correctly estimate the relative source contributions and related uncertainties, the endmember variability as well as other sources of uncertainty needs to be included in the analysis. , Markov Chain Monte Carlo (MCMC)-driven Bayesian approaches have been implemented to account for multiple sources of uncertainties/variabilities . Such an approach for isotope-based source apportionment has been used in multiple studies e.g., refs , , and . The resulting probability density functions’ output from the model give a “least-biased” representation of the precision.…”

Tracing the origin of elevated springtime atmospheric sulfate on the southern Himalayan-Tibetan plateau

“…Isotope analysis is a powerful tool for ngerprinting the source/origin of a targeted molecule/species. [26][27][28] S-isotope analysis which historically has been limited to 34 S/ 32 S, has been extended to 33 S/ 32 S and 36 S/ 32 S to access 'mass-independent fractionation' (MIF) [e.g., D 33 S = ln(d 33 S + 1) − 0.515 × ln(d 34 S + 1), reported in &]. 29-32 D 33 S s 0, i.e., sulfur isotope anomaly, has proven to be a worthy geochemical tracer to decipher the origin of sulfate in both present and paleo-atmospheres.…”

“…Isotope analysis is a powerful tool for fingerprinting the source/origin of a targeted molecule/species. 26–28 S-isotope analysis which historically has been limited to 34 S/ 32 S, has been extended to 33 S/ 32 S and 36 S/ 32 S to access ‘mass-independent fractionation’ (MIF) [ e.g. , Δ 33 S = ln( δ 33 S + 1) − 0.515 × ln( δ 34 S + 1), reported in ‰].…”

Sources and Long-term Variability of Carbon Monoxide at Mount Kenya and in Nairobi

“…However, the ground-truthing of the satellite observations is challenged by a deficit of atmospheric observatories and scant continuous long-term observations in the region (DeWitt et al, 2019;Henne et al, 2008b;Kulmala, 2018). Exacerbating this observational deficit, regional CO emission inventories are not well-defined as the continent possesses a unique CO emission profile, different from other regions such as Europe and South Asia (Crippa et al, 2018;Dasari et al, 2022;Hedelius et al, 2021). To advance our understanding of trends in CO over Africa and its source contributions, long-term CO measurements and isotope-based source apportionment studies are required but data availability is scarce.…”

“…The isotopic composition of CO provides insights into the relative strengths of regional CO sources and atmospheric processing (Brenninkmeijer, 1993;Dasari et al, 2022;Henne et al, 2008b;Röckmann et al, 2002).…”