An Example of an Unusual Thunderstorm-Induced Rapid Increase in Ground-Level Ozone Concentrations 5 July 2017

An unusual sudden increase in ozone concentrations measured at several air quality monitoring stations in northern Minnesota occurred during the early morning of July 5, 2017. The event was also recorded at the air quality monitoring station in Thunder Bay, Ontario. At two of the stations, ozone concentrations increased from about 20 ppb to over 50 ppb and then returned toward their typical nocturnal concentrations.

All three ozone events coincided with a thunderstorm complex in the area of the monitoring stations. While downward vertical transport is a well-known feature of thunderstorms, this event is an unusual example that illustrates the potential for thunderstorm downdrafts to enrich surface-level ozone concentrations.