Characterisation of diurnal ground level ozone concentration in urban area in Malaysia

Ground level ozone (03) can be classified as secondary air pollutant that impose harmful effects on human health, crop production and air quality. The formation of 03 is induced by the emissions of its precursors (NOx and VOCs) in process of photochemical reaction with the presence of sunlight in daytime. Meanwhile, at nighttime, since there is no sunlight, those precursors of 03 act as removal agents to reduce the 03 concentration. An effective nighttime removal rate is believed to cause decrement in next day 03 concentration, and vice versa. However, those interrelationship between daytime and nighttime 03 reaction is scarcely studied and minimally understood. Therefore, this study focused on the determination of 03, NO2 and NO concentration and explore the relationship between daytime and nighttime of 03 and its precursor in Shah Alam, Selangor. The primary data were collected by using Aeroqual S500 for 72 hours continuously. Meanwhile, the secondary data were obtained from Air Quality Division, Department of Environment (DoE), Malaysia for five years of continuous hourly average data of 03, NO2 and NO from 2006 to 2010. The obtained data were divided into daytime and nighttime and been analysed by descriptive analysis, box and whisker plot, time-series analysis, diurnal plot and multiple linear regression. The diurnal patterns of 03 in Shah Alam were showing a consistent trend with slightly different magnitude. The maximum level of 03 concentration was observed at noon time (1400 hour to 1500 hour), while its minimum level of 03 concentrations occurred at night starting from 2000 hour until dawn which is around 0700 hour to 0800 hour due to NO titration. Most of the daytime 03 concentration showed that it exceeds the permissible values recommended by MAAQG, which is 92 ppb compared to nighttime. The p-value obtained for the mean of 03 concentration was 0.00. Since the p-value were less than 0.05, so there were significant differences for the mean of 03 during daytime and nighttime in Shah Alam.