Ambient Air Quality Measurements Along High- and Low-Density Traffic Routes in Southwestern Nigeria

Ambient air quality measurements were carried out between November 2018 and October 2019 along high- and low-traffic density routes in Lagos and Ile-Ife in southwestern Nigeria in order to evaluate the air pollution loads at each airshed. Four sampling points were established during dry and wet season periods over an averaging period of 24 h, while meteorology and ambient measurements were carried out simultaneously at each of the sampling points. Particulate matter (PM_2.5) concentrations were measured using air metric particulate matter sampler, while ambient gaseous concentrations of carbon monoxide (CO), nitrogen oxides (NO₂)_, sulfur dioxide (SO₂), ozone, and volatile organic compounds (VOC) were measured using CO data logger, Ogawa sampler, and 3 M air monitor badge. The samples collected using the Ogawa sampler and 3 M air monitor badge were analyzed using ion chromatography and gas chromatography. The measured ambient mean PM_2.5 concentration in Lagos was 152.6 ± 61.7 µg/m³, while that of Ile-Ife was 93.1 ± 2.2 µg/m³. The measured concentrations of NO₂ in Lagos ranged from 22.0 to 65.0 µg/m³ and that for Ile-Ife ranged from 10.0 to 55.0 µg/m³. SO₂ concentration ranged from 20.6 to 58.1 µg/m³ in Lagos and 16.4 to 60.7 µg/m³ in Ile-Ife. CO concentrations in Ile-Ife sampling points ranged from 1030.7 to 3000.4 µg/m³, while that of Lagos sampling points ranged from 1030.7 to 3664.6 µg/m³. Higher average level (40.0 ± 8.5 µg/m³) of VOC was recorded in Lagos than Ile-Ife with an average value of 17.3 ± 5.5 µg/m³. All ambient pollutant values were below Federal Ministry of Environment and World Health Organization limits except PM_2.5 and SO₂. Therefore, toxicity potential data are useful for better air quality management in compliance with local statutory limit.