Diurnal variations of ground-level ozone in three port cities in Malaysia

The diurnal variations of ground-level ozone (O₃) concentrations along a gradient of three major port cities (Klang, Perai, and Pasir Gudang) in Malaysia were evaluated. Annual monitoring records (2009) of O₃, nitrogen dioxide (NO₂), nitric oxide (NO), carbon monoxide (CO), sulfur dioxide (SO₂), and particulate matter (PM₁₀) were obtained. Weather-influencing parameters such as incoming solar radiation, temperature, relative humidity, and wind speed were also analyzed. Although an overwhelming majority (99.9 %) of the recorded data are below the prescribed levels in the Malaysian Ambient Air Quality Guidelines (MAAQG), a number of exceedances (0.1 %) (>100 ppb) have been recorded in Klang and Pasir Gudang. The annual hourly average concentrations of O₃ were 20.3?±?18.2, 15.4?±?15.8, and 14.4?±?13.1 ppb for Klang, Perai, and Pasir Gudang, respectively. The diurnal cycles of ground-level O₃ concentrations and cluster analysis suggest that a unimodal peak occurs between 1 p.m. and 3 p.m., and the highest O₃ concentrations were observed during the first quarter of 2009 as a result of the higher rate of local photochemical production. Results of principal component analysis showed that the contributions to O₃ level variation by meteorological variables (UVB, temperature, relative humidity, and wind speed) are higher at 47.7, 39.5, and 18.2 % than those of primary air pollutants (NO_x, CO, SO₂, PM₁₀) at 28.9, 32.6, and 45 % for Perai, Pasir Gudang, and Klang, respectively. The exposure of the population in the three port cities to the elevated levels of ozone during January–May months validated the increasing threat and risks that ozone presents to humans. Result indicated that the concentration of O₃ in the three ports was still below the maximum permissible values prescribed by the MAAQG, and expansion in shipping industries is possible in exaggerating O₃ problems especially in Klang.