The AirNow image above shows that there was an increased level of Ozone in regions of Maryland on September 11th. Large portions of Maryland had a Yellow Ozone AQI level (Moderate) and the Beltsville area had an Orange Ozone AQI level (Unhealthy for Sensitive Groups.) In the AirNow Tech graph below shows that around noon the Beltsville site recorded having around 90 ppb.
An Ozone Sonde launched on September 11th by the UMBC Atmospheric Lidar Group corroborates that data as the Ozone Sonde reported a mixing ratio of .09 to .095 ppmv (parts per million by volume.) The Moderate Ozone level extended to be around 2 kilometers high.