Delaware air quality today

Delaware’s mean elevation is about 60 feet, the lowest of any state, and everything except the northern tip above the Christina River lies on the Atlantic Coastal Plain. Nothing here inverts and nothing gets held against a ridge. Position does the work terrain does elsewhere: the state sits at the downwind end of the Washington–Baltimore–Philadelphia corridor, inside the multi-state Ozone Transport Region the Clean Air Act created for that specific problem. Delaware’s own Division of Air Quality has argued in its planning documents that attainment is not reachable on in-state cuts alone, because most of what the monitors here measure was made upwind.

Ozone is the pollutant that behaves this way, because it is not emitted directly. It assembles over hours in sunlight, downwind of whatever released its ingredients. The bay and the ocean add a second step: air that drifts offshore keeps reacting and returns on the afternoon sea breeze, so a coastal monitor can read higher than the traffic near it would explain. Delaware has sources of its own, concentrated in the north — the I-95 spine through New Castle County, and the Delaware City refinery on the river, which its operator rates at 180,000 barrels a day.

Monitoring and permitting sit with the Division of Air Quality inside DNREC. This site has no Delaware city page at all yet. That is a gap in our coverage rather than a finding about the air over Wilmington or Dover.