Assessment of Weekday and Weekend Variations on Ground Level Ozone and Nitrogen Dioxide Concentration in Jeli, Kelantan

Abstract

This study examines the variations in ground-level ozone (O₃) and nitrogen dioxide (NO₂) concentrations between weekdays and weekends in Jeli and their relationship with traffic volume. Data were collected over two weeks in August 2024 using the Aeroqual S500 device and manual traffic counting. The results showed that NO₂ concentrations were lower on weekends, with median values ranging from 20 to 40 parts per billion (ppb), while O₃ concentrations were higher (15–30 ppb) compared to weekdays (10–20 ppb). This trend was attributed to reduced nitrogen monoxide emissions and enhanced photochemical reactions under lower NO₂ conditions. Traffic volume was significantly higher on weekdays, peaking during morning (7–9 a.m.) and evening (4–6 p.m.) rush hours, with Class 1 vehicles averaging 400 vehicles/hour on weekdays and 300 vehicles/hour on weekends. Consequently, NO₂ concentrations were higher on weekdays (60–80 ppb median values, peaking at 140 ppb). Statistical analyses, including T-tests, indicated no significant differences in mean concentrations between weekdays and weekends. Pearson correlation analysis confirmed a moderate positive relationship between traffic volume and NO₂ (0.410), while O₃ levels were influenced by sunlight intensity and atmospheric chemistry. These findings highlight the impact of traffic emissions on NO₂ and the importance of photochemical processes in O₃ variations, emphasising the need for effective air quality management strategies.