The word "Africa" often evokes romantic images of elephants crossing the Kalahari, thundering water at Victoria Falls, or panoramic views from Table Mountain.But an increasingly common sight for Africans -- especially those in Nigeria -- is that of smog, rubbish and polluted water, according to a new report.Four of the worst cities in the world for air pollution are in Nigeria, according to data released by the World Health Organization (WHO).Onitsha -- a city few outside Nigeria will have heard of -- hasthe undignified honor of being labeled the world's most polluted city for air quality, when measuring small particulate matter concentration (PM10).A booming port city in southern Nigeria, Onitsha recorded 30 times more than the WHO's recommended levels of PM10.Named and shamedThe other three cities named and shamed in the WHO report for high PM10 levels are the transport hub of Kaduna, in the north, which came fifth, followed by the cities of Aba -- in sixth place -- and Umuahia, in 16th position, which are both trade centers in southern Nigeria.Last year, the World Bank reported that 94% of the population in Nigeria is exposed to air pollution levels that exceed WHO guidelines (compared to 72% on average in Sub-Saharan Africa in general) and air pollution damage costs about 1% post of Gross National Income. By CNN

Bad news for Nigeria. But the slums are too much here in Naija sha.