Credit: Urban environments that are already polluted can interact with polluting particles to create more intense smog and haze , according to scientists in China and the US . The study revealed the morphology of black carbon , a substance that contributes to haze , global warming and the ultra fine particulates , PM2.5 , which can cause human respiratory problems . The morphology modification of black carbon occurred in four to six hours in Beijing , four times more quickly than in Houston , which has cleaner air . Scientists have said it is important to investigate the interaction of primary pollutants with specific atmospheres in order to reduce air pollution .
Urban environments that are already polluted can interact with polluting particles to create more intense smog and haze , according to scientists in China and the US . The study revealed the morphology of black carbon , a substance that contributes to haze , global warming and the ultra fine particulates , PM2.5 , which can cause human respiratory problems . The morphology modification of black carbon occurred in four to six hours in Beijing , four times more quickly than in Houston , which has cleaner air . Scientists have said it is important to investigate the interaction of primary pollutants with specific atmospheres in order to reduce air pollution .