Last year: #14
Ozone pollution rank: Not in the top 25
Louisville's location on the Ohio River spurned its growth into a major U.S. shipping port and is the reason behind its nickname the "River City." However, these busy ports, along with heavy traffic congestion and power plant fumes, are the reason Louisville has crept into the ranks as America's 10th most polluted city. City legislation won't do much to fix the problem: Pollution officials say as much as 90 percent of fine particles from coal-burning power plants blow in from other regions.
