Fluctuations in nighttime ground-level ozone concentrations during haze events in Malaysia
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Fluctuations in nighttime ground-level ozone concentrations during haze events in Malaysia Syabiha Shith 1
&
Norrimi Rosaida Awang 2 & Mohd Talib Latif 3 & Nor Azam Ramli 1
Received: 21 May 2020 / Accepted: 13 August 2020 # Springer Nature B.V. 2020
Abstract This study focused on O3 variations and the titration effects of NOx during nighttime at urban, industrial, sub-urban and background sites. Nighttime O3 concentration variations and the presence of high particles with an aerodynamic diameter of less than 10 μm (PM10) were examined because haze disturbs the photochemical reactions of O3. Hourly data on O3, NO2, NO and PM10 concentrations provided by the Air Quality Division of the Department of Environment were divided into two groups of daytime and nighttime and analysed. The maximum O3 concentrations during daytime were generally observed during noon. At nighttime, the concentration of O3 decreased, indicating that destruction activities occurred mainly via titration. The retention of O3 during daytime caused the nighttime O3 during haze events to be higher than that during normal days. Apparent fluctuations in nighttime O3 concentrations were observed in the urban site (20 ± 13 ppb) during haze events. The NO2/NO ratio in the urban site during haze was higher than that on normal days; amongst the sites, the urban one had the highest value (6.6). Results indicated that during haze, the reactions between NO and O3 were enhanced at nighttime, leading to low nighttime NO concentrations. The low nighttime NO concentrations led to low nighttime NO titration rates, which enabled O3 to persist in ambient air. Nighttime O3 was not completely absent due to anthropogenic sources. This condition accelerated NO titration to NO2, thus promoting O3 production even during haze. Keywords Anthropogenic sources . Particulate matter . Photochemical reaction . Titration rates . Urban site
Introduction O3 exists as a secondary pollutant in the lower atmosphere, where its formation and destruction highly depend on UV radiation and the intensity of its precursors, such as NOx (Ainsworth et al. 2012; Hassan et al. 2013; Alghamdi et al. 2014). Aside from being a secondary pollutant that requires UV light to complete its photochemical reactions, O3 is a noxious air pollutant and recognised as the second most significant air pollutant in Malaysia (Rahman 2013). O3 is toxic to humans and vegetation
* Syabiha Shith [email protected] 1
Environmental Assessment and Clean Air Research, School of Civil Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Penang, Nibong Tebal, Malaysia
2
Faculty of Earth Science, Universiti Malaysia Kelantan Kampus Jeli, Locked Bag No. 100, 17600 Jeli, Kelantan, Malaysia
3
Department of Earth Sciences and Environment, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia
at the ground level due to its capability to oxidise biological tissues (Brimblecombe 2009; Pugliese et al. 2014). The transformational characteristics of O3 during
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