Philadelphia’s air quality flirted with ‘hazardous’ levels Wednesday, one of the most unhealthy days for Philly air quality since 2008

The color-coded air quality index for fine particulate matter in Philadelphia on Wednesday bordered between the “very unhealthy” purple range and “hazardous” maroon range Wednesday evening, reaching the worst level since at least 2008 if not before, according to historical EPA data.

Though air quality was poor all day, the index bounced around until it tipped into the highest level, maroon, in the evening.

The U.S. Environmental Protection Agency pulls data from gauges that measure various pollutants in real time. In this case, the EPA uses data collected by Philadelphia’s Air Quality Management Services.

The EPA sets limits for each pollutant for its air quality index (AQI). The level of each pollutant is color-coded based on the highest daily AQI value at selected monitors. The Philadelphia Health Department lists six levels, from lowest to highest: green, yellow, orange, red, purple, and maroon — a level considered “hazardous.”

On Wednesday morning, the AQI for PM2.5, or fine particulate matter, in Philadelphia reached into the purple range, meaning that the air was “very unhealthy” for the time it was measured. But levels continued to climb and by 8:30 p.m. they reached into maroon.

The Inquirer examined historical EPA data stretching to 1999 for Philadelphia, and the only other time air quality reached as far as purple was on April 21, 2008. The EPA data do not contain an explanation why the levels were so high on that date.

However, news accounts from the Inquirer and Daily News show that there was an overnight, seven-alarm warehouse fire in Frankford that day. The fire destroyed the building, prompted hundreds of firefighters to respond, damaged seven homes, and turned the dark sky fiery orange.

PM2.5 is fine particulate matter defined as concentrations of 2.5 microns or smaller. It’s of special concern because the particles are so small — far smaller than the width of a human hair — and are easily inhaled. The World Health Organization says PM2.5 is responsible for the biggest proportion of health effects from air pollution.

Locally, the biggest typical sources of PM2.5 are emissions from gas and diesel-powered vehicles. Power plants are also a source. The particles form when emissions react in the air.

But wildfires burning in multiple Canadian provinces and territories contain a mixture of gaseous pollutants and PM2.5 is a chief component.

Particle pollution refers to a mix of solid and liquid droplets in the air. Some particles are so small that they are visible using only an electron microscope. Those particles can penetrate both indoors and outdoors because of their small size. During wildfires, concentrations can rise so high that particles are visible to the naked eye as part of the mix of gases in a haze.

The 24-hour standard as set by the EPA for PM2.5 is 35 micrograms per cubic meter.

Between 9 and 10 a.m. Wednesday, the level reached 177 at an air monitoring station on the 4000 block of Montgomery Drive in West Fairmount Park, the highest level in the city at the time.

“We’re beyond quadrupling the 24-hour standard,” said Russell Zerbo, an advocate for the nonprofit Clean Air Council in Philadelphia.

Normally, Philadelphia’s PM2.5 levels fall below the EPA limits.

Health effects can stem from short or long exposure and can range from aggravation of asthma and other respiratory illnesses to premature death in people with chronic heart or lung diseases. Children and seniors are most vulnerable.

But when levels are so high, they can impact almost anyone.

According to the Centers for Disease Control and Prevention, particle pollution is linked to: