Investigation of the Community Multiscale Air Quality (CMAQ) model using the Climate Penalty Factor (CPF)

The globally averaged surface temperature has increased by 0.85°C (±0.2°C) in the last century, and the global mean temperature will likely increase in the future. Surface ozone (O3) is predicted to rise by 1-10 ppb by the end of this century due to climate change. Modeling studies suggest a worsening of air pollution and subsequent increases in mortality, morbidity, and damage to crop due to projected rising temperature, even as emissions of ozone precursors decline. The Climate Penalty Factor (CPF) has been devised to quantify the dependence of surface ozone on temperature. Here, we compute the CPF from surface observations and compare to values of CPF from output of the Community Multiscale Air Quality (CMAQ) model. Our analysis suggest the CPF within CMAQ is larger than inferred from observations acquired in the Eastern U.S. during June, July and August of 2002, 2007, and 2011. Hence we conclude CMAQ may be overestimating the potential future increases in surface ozone that could be caused by global warming.