I've seen the results from NASA testing (in 1991 or 1992, in the Readers Digest) the air entering the U.S. on the west coast from 5000 ft. above sea level up to 65,000 above sea level 150 miles west of the west coast from the Alustian (SP?) island down to the tip of Baha CA and then the same altitudes 150 miles east of the east coast from Nova Scotia down to the southern tip of the Florida keys.
The air entering the U.S. was twenty,(20%) percent dirtier than it was when it left the east coast going toward Europe
My message is we, the U.S., doesn't add to global air pollution, we clean it up
The greenies need to focus on the helping the polluting nations clean their air up, not on us here in the U.S.