The East Coast of the US is featured in this MODIS Terra image, captured July 11, 2006. The region has experienced high temperatures - the haze you see in the image is likely a result of this. Smog (a word coined from the words 'smoke' and 'fog') is a combination of various gases with water vapour and dust. A large part of the gases that form smog is produced when fuels are burnt; when heat and sunlight react with these gases and fine particles in the air, smog can form.
The black lines in the image show the outlines of the US states pictured. From the top, and left to right, they are New York State, Vermont, New Hamshire, Massachusetts, Connecticut, Rhode Island, Pennsylvania, New Jersey, Delaware, Maryland, and Virginia.