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Wildfire smoke contributes to air quality exceedances in May

  • 6/1/2023 4:11:00 PM
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Des Moines, IA – The Air Quality Bureau has recorded 33 exceedances of the National Ambient Air Quality Standards (NAAQS) over the last 14 days. Smoke from wildfires in Northern Canada contributed to 32 ozone exceedances and one fine particulate matter (PM2.5) exceedance between May 18th and May 31st. Iowa has averaged less than four ozone exceedances per year over the last five years.  These exceedances are the first of the NAAQS measured in Iowa this year.

Between May 18th and May 31st, 32 exceedances of the eight-hour ozone NAAQS were measured across Iowa. The locations and number of exceedances were: Clinton (3), Coggon (4), Davenport (2), Emmetsburg (4), Pisgah (6), Cedar Rapids (4), Scott County Park (5), and Waverly (4). The days with the highest ozone exceedances were May 23, 24, and 29; six exceedances occurred each day.

All 32 ozone exceedances were at a concentration level that EPA defines as “unhealthy for sensitive groups.” Groups sensitive to ozone include people with lung diseases such as asthma, older adults, children and teenagers, and people who are active outdoors.

An exceedance of the NAAQS for fine particulate matter was also recorded at Emmetsburg on May 18. The national standard for fine particulate matter is 35 micrograms per cubic meter (µg/m3) averaged over a 24-hour period, and the 24-hour average at Emmetsburg on that day was 46.7 µg/m3. This level is considered “unhealthy for sensitive groups.” Groups sensitive to particulate matter include people with heart or lung disease, older adults, children and teenagers, and outdoor workers.

Wildfire smoke carries large amounts of particulates and gases that may act as ozone precursors and can lead to exceedances of the NAAQS for both fine particulate matter and ozone. Smoke is lofted high into the air by the heat produced and can be transported by winds far from its origin. The smoke will cool depending on the current weather conditions and may rapidly descend or remain aloft. Air quality will be negatively impacted if it descends and reaches the surface.

Smoke from wildfires in Canada impacted Iowa beginning on May 18, with lingering influences extending to the end of the month. Intermittent and patchy smoke episodes are possible as long as the wildfires remain out of control.

Real-time air quality maps and information about the air quality index can be found on EPA’s site. A graphic approximation of the extent and trajectory of the smoke plume can be seen on the map at EPA’s specific guidelines on what precautions can be taken to minimize the impact of high ozone and fine particulate levels are available at Generally speaking, they involve limiting outdoor activities, especially prolonged outdoor exertion.