Atmospheric Volatile Organic Compounds and Ozone Creation Potential in an Urban Center of Southern Nigeria

Abstract

The relative contribution of individual volatile organic compounds (VOC) species to photochemical ozone formation depends on their atmospheric concentrations and their oxidation mechanism. In an attempt to evaluate the ozone creation potential of ambient VOCs captured in an urban settlement of Benin City, Nigeria, the VOCs concentrations data collected in field studies at nine measurement sites of different air quality in the city and a background site were analysed. Air samples were collected at human breathing height of 1.5 meters from ground level at each site. Active sampling method using the low volume sampling pump (Acuro, Drager, Lubeck, Germany) was used to drawn the air into the tube; the absorbent was Chromosorb 106. The sampling periods were between May 2010 and June 2011; the period covered both dry and wet seasons. The adsorbed gases were desorbed using solvent extraction method with carbon disulphide as solvent. The extracted solutions were analyzed with gas chromatography and mass spectrometer. The observed concentrations of individual VOCs were determined and maximum incremental reactivity (MIR) coefficient along with rate constants of VOC-OH reactions were applied to assess the ozone formation potential of individual VOC in the ambient atmosphere. Sixteen VOC species were observed at various sites with mixing height in decreasing order: toluene (5.82), mp-xylene (3.58), ethylbenzene (3.46), benzene (2.29), and n-butane (0.84). The ozone formation potential study revealed that, ranking by propyl-equivalent, the alkanes included in this study account for 58% of the total propyl-equivalent concentration. The total ozone creation potential in the atmosphere of the Benin City was calculated to be 281.1 µg/m3. A comparison of total ozone formation potential (OFP) in our study with results obtained from other cities of the world revealed that the total concentration of ozone production in our study is threefold lower than the values reported in China city of Foshan. It is suggested that the sources of this pollutant need to be monitored in the area as a way of curtailing the impact of ozone in this city.

Volatile Organic Compound Composition of Urban Air in Nairobi, Kenya and Lagos, Nigeria

“…Other measurements of VOC concentrations in Lagos have been made by Olumayede (2014) [96]. They determined a lower OFP in Benin City, Nigeria than determined in this study for Lagos roadside sites (1184 µgm −3 ) (although also monitoring fewer species) at a total of 281.1 µgm −3 , with the largest contributor being m,p-xylene at 25.7 µgm −3 .…”

Methane Emission Estimation and Dispersion Modeling for a Landfill in West Java, Indonesia

“…After the inventory data had been obtained, calculations were carried out, in order to determine the potential of surface ozone formation from the methane gas concentration. Based on this information, the potential of surface ozone formation assessment was carried out using the following equation (Olumayede, 2014),…”

Characterisation of semi-volatile hydrocarbon emissions from diesel engines

“…The ozone formation potential (OFP) of speciated alkyl-benzenes ranged from 0.406 -0.767 mg O 3 /bhp-hr for ethylbenzene and 1,2,4-trimethylbenzene respectively and OFP values of 0.119 mg/bhp-hr and 0.018 mg/bhp-hr were reported for octane and nonane respectively, where bhp-hr is brake horsepower-hour. In another study by Olumayede, the contribution of individual VOCs to photochemical ozone formation in Southern Nigeria was studied (Olumayede, 2014). The following photochemical O 3 formation potentials were reported: 25.7 µg/m 3 for m,p-xylene, 11.02 µg/m 3 for ethylbenzene, 26.43 µg/m 3 for undecane, 18.85 µg/m 3 for 1,2,4-trimethylbenzene and 12.27 µg/m 3 for toluene.…”