Global multi-year O<sub>3</sub>-CO correlation patterns from models and TES satellite observations

Abstract

Abstract.The correlation between measured tropospheric ozone (O 3 ) and carbon monoxide (CO) has been used extensively in tropospheric chemistry studies to explore the photochemical characteristics of different regions and to evaluate the ability of models to capture these characteristics. Here, we present the first study that uses multi-year, global, vertically resolved, simultaneous and collocated O 3 and CO satellite (Tropospheric Emission Spectrometer) measurements, to determine this correlation in the middle/lower free troposphere for two different seasons, and to evaluate two chemistry-climate models. We find results that are fairly robust across different years, altitudes and timescales considered, which indicates that the correlation maps presented here could be used in future model evaluations. The highest positive correlations (around 0.8) are found in the northern Pacific during summer, which is a common feature in the observations and the G-PUCCINI model. We make quantitative comparisons between the models using a single-figure metric (C), which we define as the correlation coefficient between the modeled and the observed O 3 -CO correlations for different regions of the globe. On a global scale, the G-PUCCINI model shows a good performance in the summer (C = 0.71) and a satisfactory performance in the winter (C = 0.52). It captures midlatitude features very well, especially in the summer, whereas the performance in regions like South America or Central Africa is weaker. The UKCA model (C = 0.46/0.15 for July-August/December-January on a global scale) performs better in certain regions, such as the tropics in winter, and it captures some of the broad characteristics of summer extratropical correlations, but it Correspondence to: A. Voulgarakis (avoulgarakis@giss.nasa.gov) systematically underestimates the O 3 -CO correlations over much of the globe. It is noteworthy that the correlations look very different in the two models, even though the ozone distributions are similar. This demonstrates that this technique provides a powerful global constraint for understanding modeled tropospheric chemical processes. We investigated the sources of the correlations by performing a series of sensitivity experiments. In these, the sign of the correlation is, in most cases, insensitive to removing different individual emissions, but its magnitude changes downwind of emission regions when applying such perturbations. Interestingly, we find that the O 3 -CO correlation does not solely reflect the strength of O 3 photochemical production, as often assumed by earlier studies, but is more complicated and may reflect a mixture of different processes such as transport.

The ENSO signal in atmospheric composition fields: emission-driven versus dynamically induced changes

“…Such correlations have been used in several studies (e.g. Kim et al, 2013;Voulgarakis et al, 2011, and references therein) going back to Fishman and Seiler (1983) to identify regions of photochemically produced O 3 (positive correlations) and O 3 from other sources (e.g. downward transport from stratosphere) as well as O 3 loss due to chemistry or deposition (negative correlations).…”

Evaluation of the new UKCA climate-composition model – Part 2: The Troposphere

“…However, the lack of isoprene in StdTrop and its impact on chemical production of O 3 is also a contributing factor (Wild, 2007). Further comparisons of UKCA relative to global O 3 and CO observations from the TES instrument can be found in Voulgarakis et al (2011, and more recently, in Telford et al (2013).…”

Global O<sub>3</sub>–CO correlations in a chemistry and transport model during July–August: evaluation with TES satellite observations and sensitivity to input meteorological data and emissions

“…The observed O 3 -CO correlation coefficients and linear regression slopes have been used to evaluate the capability of chemistry and transport models (CTMs) to produce proper O 3 levels from its precursors for the right reasons (e.g., Chin et al, 1994;Mauzerall et al, 2000;Voulgarakis et al, 2011). Shim et al (2009) examined the Mexico City pollution outflow using O 3 , CO, and their correlations from TES as well as aircraft measurements obtained during the Megacity Initiative: Local and Global Research Observations (MILAGRO) and Intercontinental Chemical Transport Experiment (INTEX-B) campaigns.…”