Abstract
Over the past 30 years, various studies in Nigeria have monitored atmospheric particulate matter loads and elemental composition of ambient air around diverse receptor sites. A comparative discussion of the different sampling techniques, pre-treatment and analytical methods employed between 1985 and 2015. Air pollution indices from studies covered in this review were compared to relevant guideline standards such as the World Health Organization (WHO) 24-hr guideline and the United States Environmental Protection Agency (USEPA)'s National Ambient Air Quality Standard (NAAQS) daily permissible limits for fine particles of less than 2.5 micrometers in diameter (PM2.5) and coarse dust particles with a diameter of 10 micrometers (PM10) in ambient air. In addition, the sources of data for the average concentrations for PM2.5, PM10 and related metallic elements during 1985-2015 were assessed. Attempts were also made to compare varied particulate matter loads of atmospheric micro-environments in Nigeria with comparable micro-environments in selected cities around the world. Results showed that PM2.5 concentration ranged from 5-248 μg/m3, while PM10 concentration ranged from 18-926 μg/m3, revealing that about 50% of the particulate matter loads in Nigeria exceeded both the WHO (25 μg/m3, 50 μg/m3) and NAAQS (35 μg/m3, 150 μg/m3) guideline limits for PM2.5 and PM10 respectively. PM2.5/PM10 ratios for the selected studies fall below the WHO guideline (0.5-0.8), suggesting that Nigerian aerosols are mainly made up of coarse, rather than fine particles. In addition, the order of the average highest concentrations of metallic elements for PM2.5 were magnesium (Mg) > strontium (Sr) > potassium (K) > zinc (Zn) > iron (Fe) > sodium (Na) > aluminium (Al) > chlorine (Cl) > lead (Pb) > silicon (Si), while those of PM10 were Sr > Zn > Fe > Mg > calcium (Ca) >Na > Pb > manganese (Mn) > K > Al. Seasonal variation of particulate matter loads revealed higher concentrations during the dry season than during the rainy season. In addition, particulate matter loads in rural areas were generally lower than in urban areas. Wind-blown dust from the Sahara Desert is the major contributor to particulate matter loads in northern zones of the country, while sea spray and crustal matter are the highest contributors to particulate matter loads in southern zones.
Highlights
Particulate matter is the term given to the tiny particles of solid or semi-solid material found in the atmosphere as suspended mixtures
Results showed that PM2.5 concentration ranged from 5-248 μg/m3, while particles with a diameter of 10 micrometers (PM10) concentration ranged from 18-926 μg/m3, revealing that about 50% of the particulate matter loads in Nigeria exceeded both the World Health Organization (WHO) (25 μg /m3, 50 μg/m3) and National Ambient Air Quality Standard (NAAQS) (35 μg/m3, 150 μg/m3) guideline limits for PM2.5 and PM10 respectively
Meteorological data depicting seasonal variation in horizontal visibility of four climatic zones (Sahel, North Central, Southern and Coastal zones) in Nigeria was analyzed over a 30 year period (1984-2013) and the results generally showed that good visibility was obtained in the wet season due to the influence of moisture-laden south-easterly wind blowing in from the Atlantic Ocean resulting in rainfall that impinges on air-borne particulates leading to reduced aerosol loadings.[34]
Summary
Particulate matter is the term given to the tiny particles of solid or semi-solid material found in the atmosphere as suspended mixtures. The chemical complexity of airborne particles makes it imperative to consider the composition and sources of selected primary and secondary particulates deemed to be of health concern. Over the past 30 years, various studies in Nigeria have monitored atmospheric particulate matter loads and elemental composition of ambient air around diverse receptor sites. Attempts were made to compare varied particulate matter loads of atmospheric micro-environments in Nigeria with comparable microenvironments in selected cities around the world. Results showed that PM2.5 concentration ranged from 5-248 μg/m3, while PM10 concentration ranged from 18-926 μg/m3, revealing that about 50% of the particulate matter loads in Nigeria exceeded both the WHO (25 μg /m3, 50 μg/m3) and NAAQS (35 μg/m3, 150 μg/m3) guideline limits for PM2.5 and PM10 respectively. Particulate matter, Composition, Pollution, Source apportionment J Health Pollution 10: 1–18 (2016)
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