Wildfires that began at Fort Knox last week have died down after blanketing much of Louisville with smoke.The fires burned a wooded training area at the fort, and could have been caused by tracer bullets, which contain burning phosphorous. The subsequent smoke and ash blew northward to Louisville, where Air Pollution Control District spokesperson Matt Stull says an air quality alert was issued for the weekend."Typically in the summertime when we have high levels of ozone, we issue those alerts when we get into the unhealthy for sensitive groups range, but this weekend we were a step above that," he says.Stull says rain Monday has restored air quality. Fort Knox spokesperson Anne Torphy says crews from around the area are monitoring the fires, which are now smoldering."We're really at the mercy of the weather," she says. "If it continues to rain, that will help tremendously, but if we get more dry weather or if winds kick up, then we'll have to re-assess the situation."