Quantifying the weekly cycle effect of air pollution in cities of China

The weekend effect, i.e., the concentration of air pollutants is different from weekends to weekdays, has been explored since the 1970 s. In most studies, the weekend effect is referred to the change of O[Formula: see text] , i.e., lower emission of NO[Formula: see text] on weekends leads to a higher concentration of O[Formula: see text] . Determining whether it is true can provide insight into the strategy of air pollution controlling. In this study, we explore the weekly cycle of cities of China based on the weekly cycle anomaly (WCA), which is proposed in this paper. The advantage of using WCA is that we can avoid the influence of other change components such as the daily cycle and the seasonal cycle. The p values of the significant tests from all cities are analyzed for obtaining a whole picture of the weekly cycle of air pollution. The result shows that the concept of the weekend effect is not proper for cities in China, as many cities reach the valley phase of the emission on weekdays but not weekends. Thus, researches should not pre-assume that the weekend is the low emission scenario. We focus on the anomaly of O[Formula: see text] on the peak and the valley of the emission scenario estimated by the NO[Formula: see text] concentration. Through the analysis of the distribution of the p values of all cities, we show that almost all cities in China have weekly cycle of O[Formula: see text] corresponding to the weekly cycle emission of NO[Formula: see text] , i.e., O[Formula: see text] of the peak time of NO[Formula: see text] is less than valley time. The cities of the strong weekly cycle are located in four regions, i.e., the Beijing-Tianjing-Hebei region, the Shandong Peninsula Delta, the Yangtze River Delta, and the Pearl River Delta, and these regions are also the regions with relatively severe pollution levels.