EPA in Illinois

Union Station in Chicago Platform Air Quality Monitoring Frequently Asked Questions

On this page:

Q:  Why did EPA monitor particulate matter at the train platforms at Union Station?

A:  EPA conducted the monitoring in response to concerns about air quality on the train platforms at Union Station. 

Q: What pollutants did EPA monitor?

A: We monitored short-term concentrations of PM2.5.

Q: What is PM2.5? What are the health effects?

A: PM2.5 is particulate matter that is 2.5 micrometers (µm) in diameter and smaller. PM2.5 is sometimes referred to as fine particulate matter Exit. PM2.5 is a complex mixture of extremely small particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles. The size of particles is directly linked to their potential for causing health problems. EPA is concerned about particles that are 2.5 µm in diameter or smaller because those are the particles that generally pass through the throat and nose and enter the lungs. Once inhaled, these particles may affect the heart and lungs and cause serious health effects. The particulate matter measured in this survey is primarily from diesel exhaust. In addition to contributing to particulate matter, diesel exhaust contains many other harmful pollutants, including carbon monoxide, benzene, formaldehyde, and nitrogen oxides.

Q: What are EPA’s next steps?

A: EPA is discussing the results of the study with Metra, Amtrak and representatives of several buildings with ventilation systems that impact air quality at Union Station. Short-term options to improve air quality on the train platforms include optimizing the existing ventilation systems above Union Station and changing operational procedures. Long-term options include installation of additional ventilation systems and measures to reduce particulate emissions. 

Q: What air monitors were used in this study?

A: EPA's study used TSI SidePak Personal Aerosol Monitors - Model AM510.

Q: The PM2.5 concentrations on train platforms were 23-96 percent higher than concentrations at street level - but a graph shows the average PM2.5 concentration on the south platform is 372 percent higher than the average of all background concentrations. Can you explain?

A: Both calculations are correct but they measure different things.

For each hourly platform test value, EPA calculated the percentage reduction needed to reach the street level concentration of PM2.5. The range was from 23-96 percent. From 7-8 a.m. on June 16, the street level measured 26 µg/m3 and the south platform measured 673 µg/m3, so PM2.5 reductions of 96 percent would be needed. At 6-7 a.m. on June 15, the street level measured 41.33 µg/m3 and the north platform measured 54 µg/m3, so PM2.5 reductions of 23 percent would be needed.

EPA's graph depicts average concentrations over the duration of the study on the north platform, the south platform, and at street level. Average concentrations on the north and south platforms were, respectively, 200% and 372% higher than the average concentration on the street.