Several Iowa monitoring sites recorded exceedances of the National Ambient Air Quality Standard for fine particulate matter over the Fourth of July weekend.
DNR recorded exceedance levels on real-time non-regulatory monitors and multiple news sources reported on the poor air quality over the holiday weekend. Most Iowa monitors used for regulatory purposes collect a sample over a 24-hour period and the data is only available after laboratory analysis. Lab results show fine particulate matter (PM2.5) exceeded the national standard, which is 35 micrograms per cubic meter (µg/m3) averaged over a 24-hour period.
Exceedances of the standard were recorded in Des Moines, Davenport, and Muscatine on July 4, and in Des Moines and Clive on July 5.
If 24-hour fine particulate averages are above the standard, air quality is considered “unhealthy for sensitive groups.” Averages greater than 55 µg/m3 fall into the “unhealthy” category and the EPA says, “Some members of the general public may experience health effects; members of sensitive groups may experience more serious health effects.” The weekend exceedances are the first exceedances of the NAAQS measured in Iowa this year.
On the Fourth, Davenport monitors recorded 24-hour average values of 48 µg/m3 at Hayes Elementary and 62.8 µg/m3 at Jefferson Elementary. Muscatine recorded 44.8 µg/m3 at the former Garfield School. Des Moines recorded 108.7 µg/m3 at the Polk County Health Department site, more than three times the national standard.
Lingering smoke, calm winds and additional fireworks also led to exceedance levels of 60.9 and 46.9 µg/m3 respectively at the Polk County site and the Indian Hills School site in Clive on July 5.