Preliminary Study of Ground Level Ozone Nighttime Removal Process in an Urban Area

Abstract

The depletion processes of nighhtime ground level Ozone (O3) concentrations in an urban area inMalaysia were evaluated. Annual monitoring records of O3 in Kota Bharu, Kelantan, wereobtained from Department of Environment, Malaysia and separated into daytime and nighttimeconcentrations. In Malaysia, daytime starts from 7 a.m. until 7 p.m., and 7 p.m. to 7 a.m. isdeemed as nighttime. The annual hourly average concentrations of O3 were 15.13±9.23 and5.76±5.58 ppb for daytime and nighttime, respectively. The diurnal cycles of ground-level O3concentrations suggests that a uni-modal peak occurs at 1 p.m. and high O3 concentrations wasobserved on December 2010 as a result of the higher rate of local photochemical production.Absence of photochemical reactions during nighttime identified as the main factor thatcontributed to low nighttime O3 concentrations. This study discovered that NO and NO2 playimportant role in O3 depletion process during nighhtime. Result confirmed that high nighttimeNO concentration enhanced further destruction of nighttime O3 concentrations.