Air Pollution in Delaware: Philadelphia Metro Area Ranked on Two 'Worst 25 Cities' Lists, Finds 2019 'State of the Air' Report

American Lung Association's 20th annual air quality report finds more than 4 in 10 Americans live with unhealthy air quality. All counties unchanged, New Castle County fails for ozone smog.

The American Lung Association’s 2019 “State of the Air” report found that ozone (smog) air pollution throughout much of the Mid-Atlantic often worsened when compared with last year’s report, but numbers of unhealthy days remained unchanged in Delaware, even as fine particle pollution levels showed further improvements. 

For ozone smog, the Philadelphia-Reading-Camden metro area, within Delaware including New Castle and Kent Counties, had a rank that worsened from 24th to 21st worst in the country as a result of a worse performance outside of Delaware.

The report also found that the Philadelphia-Reading-Camden metro area, while improving to its best performance for its seventh consecutive year for year-round particle pollution and meeting the national air quality standard, continued to rank among the worst in the country for this pollutant—although its rank did improve from 12th to 18th worst.  

The 20th annual air quality “report card” tracks Americans’ exposure to unhealthful levels of ozone and particle pollution, both of which can be deadly. The report also found that New Castle County posted its fewest number of days high in particle pollution (earning a “C” grade) even as both Kent and Sussex Counties had zero days of unhealthy air, earning “A” grades for the eighth consecutive year.

New Castle and Kent Counties fall into the 4-state, 16-county Philadelphia-Reading-Camden, PA-NJ-DE-MD metro area.  And Sussex County is in the 2-state, 5-countySalisbury-Cambridge, MD-DE metro area. In addition to providing metro area rankings, the 20th annual “State of the Air” report also grades and ranks individual counties.

“People living, working, or going to school in Delaware should be aware that we’re breathing unhealthy air, driven by local emissions, upwind sources, and extreme heat as a result of climate change, placing our health and lives at risk,” said Kevin Stewart, the American Lung Association’s Director of Environmental Health for Advocacy and Public Policy. “In addition to challenges here in the state, the 20th-anniversary ‘State of the Air’ report highlights that more than 4 in 10 Americans are living with unhealthy air, and we’re heading in the wrong direction when it comes to protecting public health.”

This year’s report covers the most recent quality-assured data available collected by states, cities, counties, tribes and federal agencies in 2015-2017. Notably, those three years were the hottest recorded in global history. 

Each year the “State of the Air” provides a report card on the two most widespread outdoor air pollutants, ozone pollution, also known as smog, and particle pollution, often called soot. The report analyzes particle pollution in two ways: through average annual particle pollution levels and short-term spikes in particle pollution. Both ozone and particle pollution are dangerous to public health and can increase the risk of premature death and other serious health effects such as lung cancer, asthma attacks, cardiovascular damage, and developmental and reproductive harm.

Ozone Pollution in Delaware

Compared to the 2018 report, all three Delaware counties maintained the same numbers of unhealthy days of high ozone in this year’s report.  New Castle County had the worst performance, posting a weighted average of 8.7 days per year with unhealthy levels of ozone pollution, and earning an “F” grade. Kent County averaged 1 day for a “C’ grade. And while Sussex County matched last year’s best-ever performance of 2.3 days (a “D” grade), it was the worst county in its metro area.

Nevertheless, the ranking of the Philadelphia-Reading-Camden metro area for ozone was driven by the highest levels occurring outside the state, with the worst county in the metro area being Philadelphia County, PA. 

“Ozone especially harms children, older adults and those with asthma and other lung diseases,” said Stewart. “When older adults or children with asthma breathe ozone-polluted air, too often they end up in the doctor’s office, the hospital or the emergency room. Ozone can even shorten life itself.” 

This report documents how warmer temperatures brought by climate change make ozone more likely to form and harder to clean up. This year’s report showed that ozone levels increased in most cities nationwide, in large part due to the record-breaking global heat experienced in the three years tracked in the report. 

Particle Pollution in Delaware

However, the 2019 report found there were cases in which year-round and daily particle pollution levels were lower than in the 2018 report. Nationwide, the best progress in this year’s report came in reducing year-round levels of particle pollution. The only county in Delaware posting a result for year-round particle pollution was Sussex County. Although this was the state’s best performance, historically, higher results were posted in New Castle County, which recorded “Incomplete” in this year’s report. Philadelphia County, PA, posted the highest level in its metro area for this measure. All results met the air quality standard.

“Particle pollution is made of soot or tiny particles that come from coal-fired power plants, industrial sources, diesel emissions, wildfires and wood-burning devices. These particles are so small that they can lodge deep in the lungs and trigger asthma attacks, heart attacks and strokes, and can even be lethal,” said Stewart. “Year-round particle pollution levels have dropped thanks to the cleanup of coal-fired power plants and the retirement of old, dirty diesel engines.”

“State of the Air” 2019 also tracked short-term spikes in particle pollution, as these can be extremely dangerous and even lethal. This year’s report also found that the metro areas had fewer days when short-term particle pollution reached unhealthy levels. While Kent and Sussex Counties continued their string of perfect “A” grades (with zero high pollution days), in contrast, New Castle County’s weighted average of 1.7 days high in particle pollution (a “C” grade) made this the worst polluted county in the Philadelphia-Reading-Camden metro area for this measure. Because of the improvement from last year’s “D” grade, the national rank for that metro area improved to 43rd from 31st most polluted in last year’s report,

While improvements have continued locally, many of these spikes in the western United States were directly linked to weather patterns leading to drought or to wildfire events, which are increasing in frequency and intensity in many areas of the country due to climate change. 

While the report examined data from 2015-2017, this 20th annual report online provides information on air pollution trends back to the first report. Learn more about Delaware’s rankings, as well as air quality across the nation, in the 2019 “State of the Air” report at For media interested in speaking with an expert about lung health, healthy air, and threats to air quality, contact Annette Eyer at [email protected] or 717-971-1124. 

For more information, contact:

Allison MacMunn
[email protected]

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