Interpreting space-based trends in carbon monoxide with multiple models

Sarah A Strode,Bryan N Duncan,Jean-Francois Lamarque,Jose M Rodriguez,Anne R Douglass,Michael Manyin,Luke D Oman,Louisa K Emmons,Megan Damon,Helen M Worden,Susan E Strahan,Simone Tilmes

doi:10.5194/acp-16-7285-2016

Abstract

Abstract. We use a series of chemical transport model and chemistry climate model simulations to investigate the observed negative trends in MOPITT CO over several regions of the world, and to examine the consistency of time-dependent emission inventories with observations. We find that simulations driven by the MACCity inventory, used for the Chemistry Climate Modeling Initiative (CCMI), reproduce the negative trends in the CO column observed by MOPITT for 2000–2010 over the eastern United States and Europe. However, the simulations have positive trends over eastern China, in contrast to the negative trends observed by MOPITT. The model bias in CO, after applying MOPITT averaging kernels, contributes to the model–observation discrepancy in the trend over eastern China. This demonstrates that biases in a model's average concentrations can influence the interpretation of the temporal trend compared to satellite observations. The total ozone column plays a role in determining the simulated tropospheric CO trends. A large positive anomaly in the simulated total ozone column in 2010 leads to a negative anomaly in OH and hence a positive anomaly in CO, contributing to the positive trend in simulated CO. These results demonstrate that accurately simulating variability in the ozone column is important for simulating and interpreting trends in CO.

Highlights

Carbon monoxide (CO) is an air pollutant that contributes to ozone formation and affects the oxidizing capacity of the troposphere (Thompson, 1992; Crutzen, 1973)
The hindcast simulations driven by MACCity emissions (GRef-C1, Ref-C1-SD, and C-Ref-C1) show negative trends in CO over the US and Europe that agree with the observed slope from MOPITT within the uncertainty (Fig. 2, Table 2)
We conducted a series of multi-year simulations to analyze the causes of the negative trends in MOPITT CO reported by Worden et al (2013)

Summary

Introduction

Carbon monoxide (CO) is an air pollutant that contributes to ozone formation and affects the oxidizing capacity of the troposphere (Thompson, 1992; Crutzen, 1973). Its primary loss is through reaction with OH, which leads to a lifetime of 1–2 months (Bey et al, 2001) and makes CO an excellent tracer of long-range transport Both fossil fuel combustion and biomass burning are major sources of CO. The time-dependent MACCity inventory (Granier et al, 2011) shows decreases in CO emissions from the United States and Europe from 2000 to 2010 due to increasing pollution controls but increases in emissions from China. The bottom-up inventory of Zhang et al (2009) shows an 18 % increase in CO emissions from China from 2001 to 2006, and Zhao et al (2012) estimate a 6 % increase between 2005 and 2009. There is considerable uncertainty in bottomup inventories, and comparison of model hindcast simulations driven by bottom-up inventories with observations provides an important test of the time-dependent emission estimates

Methods

Results

Conclusion