Secondary organic aerosol and ozone formation potentials from diesel engine emissions at Isale-Koto, Ilorin, Kwara State, Nigeria

Abstract

Secondary organic aerosols (SOAs) and tropospheric ozone (O₃) pose significant risks to air quality and public health in urban environments, particularly in developing regions reliant on dieselpowered machinery. This study investigates the aromatic volatile organic compounds (VOCs), benzene, toluene, ethylbenzene, and xylene isomers (BTEX) emitted from diesel grinding engines at the Isale-Koto food processing market in Ilorin, Nigeria. Passive sampling at 10 locations (5 indoor, 5 outdoor) over one month captured VOC concentrations, and then analyzed them via gas chromatography. Ozone formation potential (OFP) was estimated using maximum incremental reactivity (MIR) coefficients, while secondary organic aerosol potential (SOAP) employed reactivity-based metrics relative to toluene. Results revealed higher indoor VOC levels, with total OFP at 148.014 µg.m-³ indoors versus 128.098 µg.m-³outdoors (15.5 % increase), dominated by toluene (29-31 %) and m-xylene (25 %). Total SOAP at 4,076.82 µg.m-³ (16.4 % above outdoor levels). Toluene, m-xylene, and ethylbenzene were dominant contributors to OFP, while benzene, toluene, and ethylbenzene accounted for 84 % of SOAP due to high concentrations and reactivity. These findings highlight diesel engine exhaust as a key precursor to ozone and SOA formation, with indoor accumulation due to poor ventilation amplifying photochemical pollution at groundlevel and posing serious health risks, especially for workers exposed over long durations. The study emphasizes the urgent need for improved ventilation, cleaner energy alternatives, and emission regulations.