Driving Factors for Isoprene-Surface Ozone and Carbon Dioxide Chemistry Over an Oil Palm plantation in Malaysia
Authors: nadzir mohd shahrul mohd , Ooi Maggie Chel Gee , Harris Neil RP , Bolas Conor , Bran Sherin Hassan , Macatangay Ronald C , Chan Andy , Teh Yit Arn , Jaafar Wan Shafrina Wan Mohd , Yusup Yusri , Latif Mohd Talib , Khan Md Firoz , Ahamad Fatimah , Kho Lip Khoon , Razak A'fifah Abd , Jantan Nur Maisarah , Hawari Yahaya , Yatim Ahmad Norazhar Mohd , Hamid Haris Hafizal Abd , Maulud Khairul Nizam Abdul , Wahab Muhammad Ikram A , Sahani Mazrura , Sabuti Asnor Azrin , Nor Mohd Fadzil Firdzaus Mohd , Ariff Noratiqah Mohd , Bakar Mohd Aftar Abu , Zainudin Badrul Hisyam , Yik Lin Chin 
Published: August 2020

Abstract
Background: Biogenic Volatile Organic Compounds (BVOCs) such as isoprene (C5H8) are ozone (O3) precursors that can be emitted at significant concentrations from the oil palm tree (Elaeis guineensis). Reactions involving BVOCs can lead to increased levels of surface O3 which can signiﬁcantly impair air quality and cause crop damage. This study focuses on the link between isoprene, surface O3 and carbon dioxide (CO2) over an oil palm plantation and the effects of meteorological factors such as temperature and irradiance on the gas concentrations. The mixing ratios of isoprene, surface O3 and CO2 were measured using a portable gas chromatograph with a photoionization detector called ‘iDirac’, an EcoTech O3 analyser, and LI-COR, respectively. Atmospheric models were used for measured selected gases estimation and validation purposes.Results: Results showed that isoprene and surface O3 had maximum daytime mixing ratios of ~25 ppb and ~57 ppb, respectively. CO2 mixing ratios were high during the night compared to the day, with a maximum night-time ratio of ~883 ppm. It is also showed that suppression of isoprene emissions from plants by high CO2 concentrations during the night was due to the reduction of dimethylallyl diphosphate (DMADP) in the leaf cells. The meteorological parameters temperature and light intensity were significantly correlated with isoprene and surface O3, with r2=0.91 and p<0.01 and r2=0.87 and p<0.01, respectively. The Model of Emissions of Gases and Aerosol from Nature (MEGAN) estimated emission rates of isoprene from the oil palm plantation are in the range ~5000 to ~7000 μgm-2 h-1 which are higher than previous studies on pristine forest. This information together with the the in-situ measurement information on isoprene emission flux is then fed into the WRF-CMAQ atmospheric chemistry model to study the effect of oil palm plantation expansion over the years (2000 – 2016) on the local atmospheric chemistry.Conclusions: The in-situ of isoprene measurement in oil palm plantation has provided the variations of atmospheric concentration at different time scale which is important in giving information of surface O3 production. The relationship between isoprene-surface O3 and CO2-isoprene were interconnected at different time and influenced by meteorological factors. The model has discovered regions that are converted into oil palm plantation has experienced rise in isoprene concentration in region that are converted into oil palm plantation, and it even can be carried downwind up to 100 km inland of the emission source.