The noise pollution:

This is not like London or New York, or even Tehran, another car-clogged Middle Eastern capital. It is literally like living day in and day out with a lawn mower running next to your head, according to scientists with the National Research Center. They spent five years studying noise levels across the city and concluded in a report issued this year that the average noise from 7 a.m. to 10 p.m. is 85 decibels, a bit louder than a freight train 15 feet away, said Mustafa el Sayyid, an engineer who helped carry out the study.

A City Where You Can’t Hear Yourself Scream - New York Times