Abstract
Abstract. We assessed the sensitivity of regional CO source estimates to the modeled vertical CO distribution by assimilating multi-spectral MOPITT (Measurements of Pollution In The Troposphere) V5J CO retrievals with the GEOS-Chem model. We compared the source estimates obtained by assimilating the CO profiles and the surface layer retrievals from June 2004 to May 2005. Because the surface layer retrievals are less sensitive to CO in the free troposphere, it is expected that they should provide constraints in the CO source estimates that are less sensitive to the vertical structure of CO in the free troposphere. The inferred source estimates all suggest a reduction in CO emissions in the tropics and subtropics, and an increase in the extratropics over the a priori estimates. The tropical decreases were particularly pronounced for regions where the biogenic source of CO was dominant, suggesting an overestimate of the a priori isoprene source of CO in the model. We found that the differences between the regional source estimates inferred from the profile and surface layer retrievals for 2004–2005 were small, generally less than 10% for the main continental regions, except for estimates for southern Asia, North America, and Europe. Because of discrepancies in convective transport in the model, the CO source estimates for India and southeastern Asia inferred from the CO profiles were significantly higher than those estimated from the surface layer retrievals during June–August 2004. On the other hand, the profile inversion underestimated the CO emissions from North America and Europe compared to the assimilation of the surface layer retrievals. We showed that vertical transport of air from the North American and European boundary layers is slower than from other continental regions, and thus air in the free troposphere from North America and Europe in the model is more chemically aged, which could explain the discrepancy between the source estimates inferred from the profile and surface layer retrievals. We also examined the impact of the OH distribution on the source estimates and found that the discrepancies between the source estimates obtained with two OH fields were larger when using the profile data, which is consistent with greater sensitivity to the more chemically aged air in the free troposphere. Our findings indicate that regional CO source estimates are sensitive to the vertical CO structure. They suggest that diagnostics to assess the age of air from the continental source regions should help interpret the results from CO source inversions. Our results also suggest that assimilating a broader range of composition measurements to provide better constraint on tropospheric OH and the biogenic sources of CO is essential for reliable quantification of the regional CO budget.
Highlights
The emissions of greenhouse gases and other atmospheric pollutants have been significantly increased since the industrial revolution
We presented a global inversion analysis to quantify monthly mean CO source estimates during the period of June 2004– May 2005 using the version 5 MOPITT retrievals
Building on the work of Jiang et al (2013), we conducted a comparative analysis of the influence of the MOPITT profile and surface layer retrievals on the inferred CO source estimates
Summary
The emissions of greenhouse gases and other atmospheric pollutants have been significantly increased since the industrial revolution. The lack of global observations of CO near the surface has implications for the use of inverse modeling to quantify CO emissions, because the modeled CO distribution in the free troposphere is affected by discrepancies in the parameterization of convective transport in models (e.g., Ott et al, 2009), the simulated chemical sink of CO (e.g., Jiang et al, 2011), and long-range transport (e.g., Arellano and Hess, 2006; Jiang et al, 2013). Jiang et al (2013) showed that lower tropospheric MOPITT V5J CO retrievals can be used to study the influence of convective transport error on CO source estimates. They compared the CO source estimates in June–August 2006, inferred from MOPITT surface layer retrievals, the profile retrievals, and the column amounts. In Appendix A we present the results of an indirect validation of the MOPITT data that was conducted to guide the filtering of the data used in the assimilation, and in Appendix B we have included a discussion of the optimization scheme used in the assimilation
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
