Let's hope it's a dirty bomb, and not a dirty nuke. From what I've read here at FR, a dirty nuke does damage in its own right, but ALSO disperses radioactive material. This would seem to be a far more serious weapon than a regular dirty bomb (e.g., one detonated with conventional explosives).
Radiation will ruin sensitive semiconductors, so contaminating the area will make semiconductor manufactoring impossible in the area for a while, plus ruining some of the most expensive real estate in America
In I think our first nuclear tests after WWII, we did an air drop ("Baker") over captured ships and other ships that we didn't need anymore. It was a mile off-target. Ships were spread out even farther than that, but the results weren't that spectacular. Then the "Charlie" test had a nuclear bomb on a cable 50 feet underwater beneath a transport. When that went off, the ship rode the blast a mile into the air before disintegrating, and a mountain of water came down on everything. There were battleships and carriers that survived both blasts, but when they came back to them the second time, the water stayed kind of hot and men were getting sick from being on those ships for too long. They couldn't wash the radioactivity off, and one of the worst things was that barnacles on the sides were actively filtering radioactive waste from the water and holding it against the ships.
There is a balance, though. Ground bursts leave the best concentrations of radiation, but it takes an air burst to get a good blast radius.
The dirty bomb is none of these. It just blows up the side of maybe one building, but the debris from it will be spread all over and be very poisonous for a long time.