dirty cities

According to the American Lung Association, 55% of Americans live in areas with unhealthy levels of ozone or particle pollution. In South Africa, Johannesburg has vehicle emissions, dust from mine dumps and untarred roads, and excessive burning of coal especially in informal settlements. Cape Town contends with tyres being burned illegally to recover scrap metal. And even small rural towns have to deal with pesticides blowing through houses. But what are the world's dirtiest cities? [via Trash Media]