A Code Orange Air Quality Action Day has been issued for all of Delaware on Tuesday, May 19, as dangerous heat and stagnant atmospheric conditions are expected to lead to elevated ozone levels across the state.
According to the Delaware Department of Natural Resources and Environmental Control (DNREC), air quality levels are forecast to reach “Unhealthy for Sensitive Groups” for ozone pollution, especially during the afternoon and early evening hours. Fine particulate matter, or PM2.5, is expected to remain in the low-Moderate category.
The combination of several meteorological factors is expected to contribute to deteriorating air quality. A temperature inversion early Tuesday morning will trap pollutants near the ground, limiting vertical mixing in the atmosphere. At the same time, light to moderate southwesterly to westerly winds will transport additional regional pollution into Delaware from upwind areas.
Adding to the concern, mostly sunny skies and temperatures soaring into the middle 90s will enhance ozone production throughout the day. Ozone pollution tends to peak during hot, sunny weather when emissions from vehicles, industry, and other sources chemically react in the atmosphere.
Sensitive groups, including children, older adults, and individuals with asthma or other respiratory conditions, are encouraged to limit prolonged outdoor activity during the afternoon and evening hours when ozone concentrations are typically highest.
Conditions may remain somewhat elevated into Wednesday as another hot day with temperatures in the mid-90s is expected across southern Delaware. Continued west-southwesterly flow will keep transporting pollutants into the region, while sunny skies will support additional ozone development. Air quality levels are forecast to remain in the Moderate range statewide.
Relief is expected to arrive Thursday as a cold front moves offshore. Northeasterly winds behind the front will usher in a cooler and cleaner air mass into the Mid-Atlantic. Increasing cloud cover and scattered rain showers are also expected to suppress ozone formation, allowing air quality levels to improve back into the Good category for both ozone and PM2.5 across Delaware.
