Impacts of holiday characteristics and number of vacation days on "holiday effect" in Taipei: Implications on ozone control strategies. (1st April 2019) - Chen, Pen-Yuan
Abstract: This study investigated the influence of holiday characteristics and numbers of vacation days on the "holiday effect" of three crucial Chinese holidays in Taipei. Surface measurements of NOx, CO, NMHC, O3, SO2, and PM10 from 13 air quality-monitoring stations of the Taiwan Environmental Protection Administration (TEPA) in the Taipei metropolitan area during holiday and non-holiday periods of 1994–2012 were used. All six pollutants were proven to exhibit holiday effects between Chinese New Year (CNY) and non-Chinese New Year (NCNY) periods. However, almost all pollutants exhibited holiday effects for the two other holidays; the exceptions were O3 between Tomb Sweeping Day (TSD) and non-Tomb Sweeping Day (NTSD) periods and CO and PM10 between Mid-Autumn Day (MAD) and non-Mid-Autumn Day (NMAD) periods. Air pollutants, including NOx, CO, NMHC, SO2, and PM10, that exhibited holiday effects had consistently lower concentrations in holiday periods than in non-holiday periods, whereas O3 concentrations were higher in holiday periods than in non-holiday periods. A widespread holiday effect with consistent signs indicates a high degree of urbanization in the study area. Compared with CNY–NCNY and MAD–NMAD periods, the TSD–NTSD period had a considerably lower difference of the titration effect, lower NOx resulting in less ozone destruction, in evening traffic hours and an inconsistent holiday effect in the daytime and nighttime, leading to the lack of O3 holiday effect. Because the MAD period had more nighttime activities than the other two holiday periods did, the MAD–NMAD period lacked CO and PM10 holiday effects. The prevalently higher ratios of CO, NMHC, SO2, and PM10 relative to NOx as a proxy of mobile sources and a lower PM2.5 /PM10 ratio in the MAD period than in the CNY and TSD periods indicate different pollution sources oriented from holiday activities. The air pollutants exhibited a weakening trend are all associated with a greater improvement in air quality during the non-holiday periods than the holiday periods, which implies successful air pollution control policies. Holiday effects of NOx, NMHC (p < 0.05), and CO (p < 0.10) are associated with mobile sources; the holiday effects for the three holidays tend to have a strong relation with the number of vacation days in a holiday, indicating that a large reduction of air pollution occurs when a holiday has a high number of vacation days, which probably encourages extensive behavioral changes. Moreover, the aforementioned conditions imply that air pollution control strategies are effective with time; pollution reduction for only 1–2 days may fail to improve ambient air quality. Holiday effects of pollutants emitted during long holiday periods have crucial implications in formulating ozone control strategies in Taiwan and in other countries with similar national or cultural holidays. Highlights: Almost all pollutants exhibited holiday effects for the three holidays. A widespread holiday effect with consistent signs indicates a high degree of urbanization in the study area. Holiday characteristics and day numbers have an effect on the significance and strength of holiday effects. A greater improvement in air quality during the non-holiday periods than the holiday periods leads to a weakening trend of holiday effects. Ozone production regime might shift from NMHC-limited to NOx -limited under a deep reduction condition.