Diurnal variation of secondary air pollutant concentrations during movement restriction orders in Johor

Abstract

Secondary air pollutants are those that are formed through chemical reactions between primary pollutants and other substances in the atmosphere. Diurnal variations in secondary air pollutants can occur due to changes in sunlight, temperature, and the presence of other chemicals in the atmosphere. Ground-level ozone is created when sunlight interacts with nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the air. This study focused on secondary air pollution levels during movement restriction orders (MCOs)using hourly average ozone data acquired from the Department of Environment Malaysia in 2020 and 2021 in Batu Pahat station. The data were analyzed using descriptive statistics, time series analysis, and diurnal plot. The diurnal pattern of ozone concentrations showed a consistent trend in the location, with the highest levels observed from noon to evening and the lowest levels at night. Additionally, the study found that ozone levels were highest during the movement control order (MCOs) compared to the conditional movement control order (CMCO) and restricted movement control order (RMCO) with mean values of 18.1 ppb, 14.5 ppb and 17.4 ppb, respectively due to increased sunlight during the summer months. The study findings can be used to identify and study the best conditions to decrease ozone air pollution.