Air quality assessment of carbon monoxide, nitrogen dioxide and sulfur dioxide levels in Blantyre, Malawi: a statistical approach to a stationary environmental monitoring station

Abstract

Air quality in urban areas is a cause of concern because of increased industrial activities that contribute to large quantities of emissions. The study assess levels and variations of carbon monoxide (CO), nitrogen dioxide (NO₂) and sulfur dioxide (SO₂) in Blantyre, Malawi using a stationary environmental monitoring station (EMS). Results show that CO level (2.47 ± 1.23 mg m^-3) were below the Malawian limit value (10.31 mg m^-3). Although, NO₂ (4.02 ± 2.47 mg m^-3) and SO₂ (8.58 ± 2.88 mg m^-3) were significantly higher than allowable Malawian Standards (0.52 and 0.23 mg m^-3, respectively). Discernible variations in hourly, diurnal, monthly and seasonal CO, SO₂ and NO₂ were apparent. Independent t-test confirmed that day time values were higher than those at night (p < 0.05). Thus, variations in local weather affect the disparity in hourly and diurnal values. Analysis of variance (ANOVA) confirmed significant variations in monthly observations. Moreover, independent t-test showed that wet season CO (2.32 mg m^-3), SO₂ (5.10 mg m^-3) and NO₂ (9.41 mg m^-3) levels were higher than dry season values (CO = 2.32 mg m^-3; SO₂ = 3.42 mg m^-3; NO₂ = 8.13 mg m^-3). A hierarchical cluster analysis (HCA) divided the 10 months into three groups based on distribution of CO, SO₂ and NO₂, air temperature, wind speed and wind direction. Furthermore, factor analysis (FA) showed that air temperature had significant contribution to variations in mean values of CO, SO₂ and NO₂ for the entire study period. The study shows a need for constant urban air quality monitoring in Blantyre and all urban areas in Malawi. It is recommended that the experimental site widen the scope of the study by utilizing the flexibility of the EMS. 

Key words: Air pollutants, principal component analysis, developing countries, environmental monitoring
station, Kaiser normalization.