On the capabilities and limitations of GCCM simulations of summertime regional air quality: A diagnostic analysis of ozone and temperature simulations in the US using CESM CAM-Chem

Abstract

h i g h l i g h t sWe conducted a diagnostic analysis of the CESM CAM-Chem and its parameterizations. We use multiple metrics including Extreme Value Theory and Mixed Model analysis. We find persistent ozone biases under all configurations of the CESM CAM-Chem. We find that the ozone is sensitive to both meteorology and vertical resolution. We urge caution in interpretation of GCCM results in light of these differences. a b s t r a c tWe conduct a diagnostic analysis of ozone chemistry simulated by four different configurations of a Global Climate-Chemistry Model (GCCM), the Community Earth System Model (CESM) with detailed tropospheric chemistry. The purpose of this study is to evaluate the ability of GCCMs to simulate future ozone chemistry by evaluating their ability to simulate present-day chemistry. To address this we chose four configurations of the CESM that differ in their meteorology (analyzed versus simulated meteorological fields), number of vertical levels, and the coupling of the ice and ocean models. We apply mixed model statistics to evaluate these different configurations against CASTNET ozone observations within different regions of the US by using various performance metrics relevant to evaluating future ozone changes. These include: mean biases and interannual variability, the ozone response to emission changes, the ozone response to temperature changes and ozone extreme values. Using these metrics, we find that although the configuration using analyzed meteorology best simulates temperatures it does not outperform a configuration with simulated meteorology in other metrics. All configurations are unable to capture observed ozone decreases and the ozone north-south gradient over the eastern US during 1995 e2005. We find that the configuration with simulated meteorology with 56 vertical levels is markedly better in capturing observed ozone-temperature relationships and extreme values than a configuration that is identical except that it contains 26 vertical levels. We recommend caution in the use of GCCMs in simulating surface chemistry as differences in a variety of model parameters have a significant impact on the resulting chemical and climate variables. Isoprene emissions depend strongly on surface temperature and the resulting ozone chemistry is dependent on isoprene emissions but also on cloud cover, photolysis, the number of vertical levels, and the choice of meteorology. These dependencies must be accounted for in the interpretation of GCCM results.

Decadal changes in summertime reactive oxidized nitrogen and surface ozone over the Southeast United States

“…In general, AM3 overestimates surface MDA8 ozone in both years by about 16 ppb on average, with NMB of 33-45 % and NME of 35-46 %. This positive bias of summertime surface ozone has been a common issue in a number of modeling studies of this region (Fiore et al, 2009;Canty et al, 2015;Brown-Steiner et al, 2015;Strode et al, 2015;Travis et al, 2016). This might be partially attributed to overestimated anthropogenic NO x emissions from nonpower plant sectors, excessive vertical mixing in the boundary layer , or underestimates of ozone dry deposition (Hardacre et al, 2015;Val Martin et al, 2014).…”

Extremal Dependence between Temperature and Ozone over the Continental U.S.

“…depending on details of the analysis (Brown-Steiner et al (2015)). The relation between ozone and temperature is complex: it is determined by the impact of meteorological factors which impact ozone such as stagnation events or cloud cover (e.g., see Jacob and Winner,2009), by temperature dependent ozone chemistry (Pusede et al (2015)) and by temperature dependent emissions(e.g., Weaver et al (2009)).…”

“…The GCM2000 simulation simulates the temperature extremes better than the REFC1SD simulation, but the REFC1SD simulation significantly underestimates the tail of the ozone distribution. Further comparison of simulation differences between CAM4-chem with specified dynamics and CAM4-chem run with online meteorology are given in Brown- Steiner et al (2015). -We propose a new method to measure the joint extremes of temperature and ozone by calculating the spectral density (ϕ) of the joint extremes of ozone and temperature.…”

“…Brown-Steiner et al (2015) has evaluated both the specified dynamics and free-running model configurations against measurements over the U.S., including comparisons…”

“…summertime ozone and temperature data (1 June to 30 August) are analyzed from both CASTNET and the three model simulations over the U.S. Ozone data is used from the first model level which provides a good estimate of the 10-meter ozone concentrations as measured by CASTNET (Brown-Steiner et al (2015)). In both CASTNET and the model data, the maximum 30 daily 8-hour average ozone concentrations (MDA8) are used.…”