Seasonal and long term variations of surface ozone concentrations in Malaysian Borneo

Malaysian Borneo has a lower population density and is an area known for its lush rainforests. However, changes in pollutant profiles are expected due to increasing urbanisation and commercial-industrial activities. This study aims to determine the variation of surface O₃ concentration recorded at seven selected stations in Malaysian Borneo. Hourly surface O₃ data covering the period 2002 to 2013, obtained from the Malaysian Department of Environment (DOE), were analysed using statistical methods. The results show that the concentrations of O₃ recorded in Malaysian Borneo during the study period were below the maximum Malaysian Air Quality Standard of 100ppbv. The hourly average and maximum O₃ concentrations of 31 and 92ppbv reported at Bintulu (S3) respectively were the highest among the O₃ concentrations recorded at the sampling stations. Further investigation on O₃ precursors show that sampling sites located near to local petrochemical industrial activities, such as Bintulu (S3) and Miri (S4), have higher NO₂/NO ratios (between 3.21 and 5.67) compared to other stations. The normalised O₃ values recorded at all stations were higher during the weekend compared to weekdays (unlike its precursors) which suggests the influence of O₃ titration by NO during weekdays. The results also show that there are distinct seasonal variations in O₃ across Borneo. High surface O₃ concentrations were usually observed between August and September at all stations with the exception of station S7 on the east coast. Majority of the stations (except S1 and S6) have recorded increasing averaged maximum concentrations of surface O₃ over the analysed years. Increasing trends of NO₂ and decreasing trends of NO influence the yearly averaged maximum of O₃ especially at S3. This study also shows that variations of meteorological factors such as wind speed and direction, humidity and temperature influence the concentration of surface O₃.