MANSFIELD — When Janene Smith asked administrators at St. Peter’s School to purchase an outdoor air quality monitor, she figured it would be a worthwhile educational tool for her middle school science classes.
But the metrics calculated by the small white machine likely have a much wider audience now.
Ohio is among multiple U.S. states experiencing decreased air quality after a series of massive wildfires in Canada.
St. Peter’s air quality monitor, manufactured by PurpleAir, is one of two in Richland County collecting publicly available data. The other, registered on PurpleAir’s website as “James Home,” is located near Bellville.
Smith has been checking the monitor’s readings daily since the school got it up and running about two weeks ago.
“I kept checking every day to make sure that it was working properly,” she said.
The air quality index (AQI) are counted on a scale of 0 to 500, with higher numbers indicating higher levels of pollution. Different zones are assigned different colors — indices 50 and below are green. Increasing ranges are marked in yellow, orange, red and purple, each indicating progressively worse pollution.
According to guidelines from the U.S. Air Quality Index, indices between zero and 50 are regarded as good. A figure between 51 and 100 is classified as acceptable; 101 to 150 is unhealthy for sensitive groups; 151 and above is unhealthy. Once an index reaches at least 301, the air is considered to be hazardous.
According to the St. Peter’s PurpleAir station, Mansfield’s AQI has ranged from 55 to 154, after EPA corrections, between Wednesday afternoon and Friday.
“The day after I started hearing about the fires, I started noticing that the colors were increasing and the numbers were ticking up,” Smith said.
“Normally it stays green, maybe slightly yellow on a hazy day. It definitely was out of the norm to see the whole eastern seaboard light up red and purple.”
The device has two sensors, which use light and shadows to measure the concentration of particulate matter in the air.
“If you’ve ever been in your house and noticed when a beam of sunshine comes through the house, all that stuff is like floating around and you can see like the dust that’s floating around — that’s basically how the sensor works,” Smith explained.
“Something passes in front of it and it blocks the light and (the machine) senses that there’s a particle.”
More specifically, the monitor tracks PM2.5 — particulate matter that are 2.5 microns or less in diameter. These tiny specks are invisible to the human eye, just a fraction of the width of a human hair.
According to the U.S. EPA, particulate matter refers to a wide range of components, including acids, inorganic compounds, organic chemicals like soot, soil or dust and biological materials like pollen and mold spores.
Larger particulate matter can cause throat and eye irritation; smaller ones can cause more serious health problems.
“I think there’s kind of a misconception that the larger the particles, the more harmful they would be if you breathe them in,” Smith said. “It’s actually these tiny particles that are the most harmful because they are small enough to get all the way into your lungs.”
Where can I find data from local PurpleAir sensors?
Data from PurpleAir monitors is aggregated and published as part of both government-run and private sector air quality maps.
PurpleAir data is available on its own website. It’s also used in air quality calculations by Weather Underground and BreezoMeter, which supplies data to the Apple weather app.
How accurate is PurpleAir data?
Scientists from the U.S. Environmental Protection Agency have found that PurpleAir sensors tend to over predict fine particle concentrations in most locations and under higher humidity when compared to regulatory-grade monitors operated in the same location.
Thus, the EPA created an equation to correct the bias and come up with a modified reading for PurpleAir equipment.
An option to have PurpleAir data adjusted based on that formula is available on the company’s online map. Users can select that option by clicking the settings wheel in the top left corner of their screen and applying the US EPA conversion.
AirNow’s fire and smoke map, which solely tracks PM2.5, uses St. Peter’s PurpleAir monitor but uses an hourly average and runs the figures through an EPA’s correction equation “to reduce bias in the sensor readings.”
Where else can I track the Air Quality Index (AQI)?
There are multiple resources for tracking the local Air Quality Index, all of which might have slightly varying numbers.
Metrics might vary due to which pollutants are being counted, how often the data is collected and averaged and whether an EPA correction formula is being used.
PurpleAir only tracks PM2.5 pollutants. While PM2.5 is the most prevalent pollutant in the wake of a wildfire, it’s not the only one that affects air quality. Many air quality index (AQI) calculations include other matter, including larger PM10 and ozone.
Both the Weather Channel and Weather Underground AQIs include carbon monoxide, nitrogen dioxide, ozone, PM2.5 and PM10 and sulfur dioxide. A separate metric on both sites tracks the amount of pollen in the air.
The government-sponsored U.S. Air Quality Index, also known as AirNow, tracks ozone and particulate matter, but its nearest stations are in Knox, Delaware and Medina counties.
IQ Air has a map that pulls data from its own air quality monitors, as well as PurpleAir and government-operated monitors.
