出版社：Chinese Association for Aerosol Research in Taiwan
摘要：There are profound impacts of Coronavirus disease-19 (COVID-19) globally, nationally andlocally. To assess the impact of COVID-19 on the hourly concentrations of particular matter < 2.5microns (PM2.5) in Lahore and Karachi, Pakistan, this study employs multifractal analysis.Comparative analysis of high frequency (hourly) PM2.5 data for both cities from February to Aprilfor 2019 and 2020 revealed inner dynamics of time series through seasonal and trend decomposition(STL) first, then multifractal detrended fluctuation analysis (MFDFA). The empirical findingsconfirmed existence of multifractality in hourly PM2.5. Based on multifractal properties, efficiencyof Lahore declines during COVID-19. Furthermore, a varying impact of COVID-19 is found on thestrength of multifractality of PM2.5 under consideration. Drastic, significant change is found onthe efficiency of air quality in Lahore before and during COVID-19 periods. Before COVID-19,PM2.5 remains relatively efficient, while during COVID-19 period it shows high multifractality, theopposite of which is true for Karachi. However, all series exhibit anti-persistent (negativelycorrelated) behavior before and during COVID-19, with respect to the remainder component ofPM2.5 concentration. This means that when PM2.5 concertation is high at a given time, in the nextperiod, the concentration will be low. Intuitively, this is accurate, given that hourly PM2.5concentrations change with economic activity, which oscillates in daily cycles of high and lowPM2.5 concentrations. In Lahore significantly lower efficiency is observed during COVID-19; noconclusion on lockdown can be made. In Karachi, higher efficiency was achieved COVID-19, whichwas well correlated with the before COVID-19 period, implying effective lockdown policy. Theconfirmation and examination of multifractality in PM2.5 concentrations of Lahore and Karachipresents researchers and policymakers with a distinct signature for the impact of COVID-19. Itprovides validation for the development of such policy evaluation tools, with reference to airquality in Pakistan.
