Question: why is riyadh so polluted?
Answer: 4. Riyadh, Saudi Arabia - 156 µg/m3 of PM 2.5. Riyadh, the largest city in Saudi Arabia also clocks in as its most polluted, with 15 times what a healthy annual PM 2.5 should be. The city attributes the high pollution days in part to sulfur dioxide in the air, which predominantly comes from industrial activity.