Model evaluation and intercomparison of surface-level ozone and relevant species in East Asia in the context of MICS-Asia Phase III - Part 1: Overview

Spatiotemporal variations of ozone (<span classCombining double low line"inline-formula">O3</span>) and nitrogen oxide (<span classCombining double low line"inline-formula">NOx</span>) mixing ratios from 14 state-of-the-art chemical transport models (CTMs) are intercompared and evaluated with <span classCombining double low line"inline-formula">O3</span> observations in East Asia, within the framework of the Model Inter-Comparison Study for Asia Phase III (MICS-Asia III). This study was designed to evaluate the capabilities and uncertainties of current CTMs simulations for Asia and to provide multi-model estimates of pollutant distributions. These models were run by 14 independent groups working in China, Japan, South Korea, the United States and other countries/regions. Compared with the previous phase of MICS-Asia (MICS-Asia II), the evaluation with observations was extended from 4 months to 1 full year across China and the western Pacific Rim. In general, model performance levels for <span classCombining double low line"inline-formula">O3</span> varied widely by region and season. Most models captured the key patterns of monthly and diurnal variation of surface <span classCombining double low line"inline-formula">O3</span> and its precursors in the North China Plain and western Pacific Rim but failed to do so for the Pearl River Delta. A significant overestimation of surface <span classCombining double low line"inline-formula">O3</span> was evident from May to September/October and from January to May over the North China Plain, the western Pacific Rim and the Pearl River Delta. Comparisons drawn from observations show that the considerable diversity in <span classCombining double low line"inline-formula">O3</span> photochemical production partly contributed to this overestimation and to high levels of inter-model variability in <span classCombining double low line"inline-formula">O3</span> for North China. In terms of <span classCombining double low line"inline-formula">O3</span> soundings, the ensemble average of models reproduced the vertical structure for the western Pacific, but overestimated <span classCombining double low line"inline-formula">O3</span> levels to below 800&thinsp;hPa in the summer. In the industrialized Pearl River Delta, the ensemble average presented an overestimation for the lower troposphere and an underestimation for the middle troposphere. The ensemble average of 13 models for <span classCombining double low line"inline-formula">O3</span> did not always exhibit superior performance compared with certain individual models in contrast with its superior value for Europe. This finding suggests that the spread of ensemble-model values does not represent all of the uncertainties of <span classCombining double low line"inline-formula">O3</span> or that most MICS-Asia III models missed key processes. This study improved the performance of modeling <span classCombining double low line"inline-formula">O3</span> in March at Japanese sites compared with MICS-Asia II. However, it overpredicted surface <span classCombining double low line"inline-formula">O3</span> concentrations for western Japan in July, which was not found by MICS-Asia II. Major challenges still remain with regard to identifying the sources of bias in surface <span classCombining double low line"inline-formula">O3</span> over East Asia in CTMs.