I stayed for a week for work ( lot of traffic that seemed typical after walking around, San Miguel Chapultepec, Mexico City, Federal District) in mornings when

I stayed for a week for work ( lot of traffic that seemed typical after walking around, San Miguel Chapultepec, Mexico City, Federal District) in mornings when I awoke and blew my nose into paper tissue it was dark with the dirt? filtered by I guess my nose/respiratory system. This has never happened to me in Northern California or living near downtown Houston/Austin, Texas.