High nighttime ozone (O 3 ) concentration levels were observed in Kemaman, Terengganu, and results were compared with those in other places in Malaysia. In this study, the contribution of precursors [nitric oxide (NO) and nitrogen dioxide (NO 2 )] and meteorological factors wind speed, and wind direction) toward long-term high nighttime O 3 over the period of 1999 to 2010 was evaluated. During this period, the recorded highest nighttime O 3 ground level was 89 ppb with more than 25% surpassing 20 ppb. Analysis shows that minimal decreasing trends were measured in Kemaman. Lower nitrogen oxide (NO x ) concentrations restricted the sinking agents; thus, reducing the depletion rates allowed O 3 to remain in the atmosphere. Minimal associations were observed between the O 3 concentration level and the speed and direction of wind. Accordingly, the largest contributor toward high nighttime O 3 ground level concentration in Kemaman was most probably NO x concentration.
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