Memphis, TN Air Quality Index (AQI) Today

By landed weight Memphis International is the second-largest cargo airport in the United States, behind Anchorage, and the FedEx Express hub built around it does the bulk of its sorting between late evening and dawn. Diesel here does not follow a commuter clock. The corridors feeding the airport, and the four road and rail bridges carrying traffic across the Mississippi, stay loaded through hours when most metros have gone quiet, releasing a share of the day’s combustion into the shallow, stable layer that forms overnight rather than into an afternoon that would mix it away.

Terrain gives that nothing to work with and nothing to fight. Downtown stands on the fourth Chickasaw Bluff, 50 to 200 feet above the floodplain, and past the bluff line the ground is flat in every direction. With no basin to hold air, the worst PM2.5 stretches here are stagnation rather than inversion: a slow, humid high sitting over the Delta with nothing to move what the corridors put out.

Fall adds a source from across the river. Rice fields in the Arkansas Delta are burned after harvest under a smoke management plan that is voluntary rather than a permit regime, and satellite work on Mississippi County, Arkansas has tracked the resulting PM2.5 plumes directly. One further complication is jurisdictional. The metro straddles Tennessee, Mississippi and Arkansas, so a single airshed sits under three state agencies at once.