Chicago recorded its worst-ever fine particle air pollution this week
EPA sensors in city, suburbs showed highest readings ever during Canadian wildfires
By Amy Qin, Matt Kiefer, Brett Chase | Chicago Sun-Times
Chicago recorded its worst-ever fine particle air pollution this week
EPA sensors in city, suburbs showed highest readings ever during Canadian wildfires
By Amy Qin, Matt Kiefer, Brett Chase | Chicago Sun-TimesThe Chicago area registered its worst fine-particulate air pollution on record this week as Canadian wildfire smoke descended on the Midwest.
The U.S. Environmental Protection Agency has been monitoring air particulate pollution in the Chicago area since 1998 to make sure that it meets healthy standards set by the federal Clean Air Act. The EPA uses an air quality index to track levels of pollution, known as particulate matter 2.5, that sends microscopic chemical particles from the wildfires. These particles, known as PM2.5, can reach deep in the lungs and can lead to serious respiratory issues with long term exposure. The higher the AQI, the worse the pollution.
A WBEZ analysis of EPA sensor data from the past 25 years shows the AQI reached a record daily high of 221 on Wednesday in Joliet. In the city of Chicago, readings peaked at 171 on Tuesday.
These are the highest readings on record for both the city of Chicago and surrounding metro area.
This high level of air pollution has sent people to the hospital, prompted warnings to stay inside and brought attention to the climate crisis. Environmental and health advocates warn that the Canadian fires may be just the beginning of health hazards during our summer months when heat, humidity and pollution combine for a toxic mix.
The Chicago area has only recorded three days since 1998 where daily AQI readings have broken above 200 into the “very unhealthy” range. All three of those daily highs were recorded from sensors outside of the city of Chicago: in Gary, Ind.; Joliet and Naperville.
Air quality readings above 150 are “unhealthy” for everyone. Daily AQIs have surpassed that level on just 39 days since 1998.The Chicago area struggles with poor air quality in general. Only 38% of days recorded by EPA sensors showed AQI readings staying within the EPA’s “good” air quality range.
As of Friday, the air was still “unhealthy” for sensitive groups, including the very young, old and those with health conditions. Sensitive populations often heed warnings throughout the summer related to unhealthy air caused by ozone pollution. These groups faced double exposure on Wednesday and Thursday when EPA also issued warnings to sensitive groups about unhealthy levels of ozone pollution.
Tuesday and Wednesday of this week reached air pollution levels unhealthy for everyone.
(Daily readings differ from the real-time AQI reported on the EPA’s AirNow.gov website. For more information, read the methodology section below.)
Many Chicagoans took extra precautions when they saw the air outside.
“I think it’s harder to breathe. I don’t feel safe really now,” said Jessie Ossorio outside the Kimball Brown Line station on Tuesday. “I will try not to be in a rush today and also try not to run…I’ll wear my mask when I’m walking outside.”
Susan Buchanan, associate professor at the University of Illinois at Chicago’s School of Public Health, says “people can have immediate health effects as soon as they go out in the first five or 10 minutes.”
Gordon Frasnrab, who has chronic obstructive pulmonary disease, acutely felt the impact of Tuesday’s air.
“I don’t have much energy, I’m coughing, my eyes are red,” said Frasnrab.
How we analyzed pollution data for this story: WBEZ acquired data from two EPA sources: the Download Daily Data tool, which provides a recent history of near -real-time sensor readings from the government’s AirNow.gov service, and the agency’s Air Quality System application programming interface, which includes historical readings dating back as far as 1998.
The sensors detect and report various types of pollution, including fine particulate matter, or PM2.5, and ozone. Readings include specific measurements of pollutants as well as air quality indices that the EPA uses to convey conditions to the public. There are 26 sensors in the Chicago Core-Based Statistical Area, which includes the city, suburbs and parts of northwest Indiana and southeast Wisconsin.
The daily data are aggregated from readings throughout a 24-hour period and don’t necessarily correspond to the highest reading in a given day. They are considered preliminary and are eventually replaced by certified AQS readings, which are only updated through April 30 of this year. An EPA spokesperson validated the methodology of comparing recent daily readings to historical AQS data and also confirmed that the sensor network recorded its highest PM2.5 pollution level ever in Chicago this week.
The AQS data contain some omissions, with some sensors reporting no data on a number of dates over the past 25 years. Most notably, there are no data points for any of the four EPA sensors located within Chicago city limits between 2011 and mid-2014, and only two sensors, on the Northwest side near North and Pulaski and Southwest side near 79th and Pulaski, report daily data after April 30. WBEZ inquired about these omissions and did not hear back from EPA by publication time.
WBEZ reporter Clare Lane contributed to this report.
Amy Qin is WBEZ’s data reporter. Follow her @amyqin12. Matt Kiefer is a data editor at WBEZ. Brett Chase covers Environmental, Planning & Public Health at the Chicago Sun-Times. Follow him @brettchase. His reporting on the environment and public health is made possible by a grant from The Chicago Community Trust.