Data provided by
Clean Air Council
live AQI index
|Air pollution level||Air quality index||Main pollutant|
|Good||7 US AQI||PM2.5|
|Open your windows to bring clean, fresh air indoors|
|Enjoy outdoor activities|
|Saturday, Aug 1|
Good39 US AQI
|Sunday, Aug 2|
Good33 US AQI
|Monday, Aug 3|
Good23 US AQI
Good31 US AQI
|Wednesday, Aug 5|
Good47 US AQI
|Thursday, Aug 6|
Moderate54 US AQI
|Friday, Aug 7|
Moderate75 US AQI
|Saturday, Aug 8|
Unhealthy for Sensitive Groups107 US AQI
|Sunday, Aug 9|
Unhealthy for Sensitive Groups108 US AQI
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Pollution levels are often described using an air quality index (AQI) level. The air quality index weighs 6 criteria pollutants for risk to health in order to provide a snapshot of the overall air quality status in a single number. In 2019, Philadelphia's monthly AQI levels varied from 25, “good,” in October, to 57, “moderate,” in July.
Summer and winter tend to be Philadelphia’s most polluted seasons, while spring and fall often experience relatively cleaner air. In 2019, Philadelphia’s most polluted months were July, December, and February, respectively.
Despite seasonal and daily fluctuations into “moderate” and “unhealthy” AQI ratings, Philadelphia has, in recent years, consistently averaged an annual AQI level in the “good” category. These annual pollution averages, however, obscure Philadelphia’s pollution events which give way to unhealthy pollution days (referred to as “action days”).
Philadelphia’s air quality is primarily afflicted by ozone. Ozone is a gas pollutant formed from precursor pollutants floating in the atmosphere and reacting in sunlight. This property of atmospheric formation differs from other frequently monitored pollutants which tend to be emitted directly from ground sources. Since a variety of volatile precursor pollutants can create ozone, it can be more challenging to manage. Attributing heightened ozone levels to specific emission sources is a near impossible endeavor. Further complicating this matter, gas pollutants like ozone and ozone precursor pollutants do not easily settle and have the ability to travel great distances.1 In the summer months, high ozone levels are frequently spread across several states.
In 2019, the American Lung Association rated Philadelphia an “F” for ozone pollution for the city’s failure to meet federal attainment levels.2 Federal regulations mandate that the number of unhealthy ozone days should not exceed an average of 3.2 across two years. From 2016 to 2018, Philadelphia experienced an average 10.8 weighted days of unhealthy ozone, far above the legal limit. In this same report, the Philadelphia-Reading-Camden area was found to rank 23rd for worst ozone pollution nationally out of 229 included metropolitan areas.
Breathing ozone can produce adverse health effects, including throat and lung irritation, chest pain, and coughing. Children, the elderly, and those with pre-existing heart or lung disease, such as bronchitis, emphysema, and asthma are more likely to experience severe complications. In Philadelphia, an estimated 901,380 residents fall into this category.
Fine particulate matter, or PM2.5, is another pollutant of concern in Philadelphia, though the city has succeeded in meeting federal attainment levels in recent years. PM2.5 describes airborne particles as measuring less than 2.5 micrometers or smaller. While PM2.5 is treated as a single pollutant, these airborne particles include a wide variety of sources and compounds. Its small size makes it among the most dangerous pollutants for its ability to penetrate deep into the lungs and, in some cases, through blood barrier, traveling throughout the body.
While the US Environmental Protection Agency (EPA) requires PM2.5 levels not to exceed 12 μg/m3, the World Health Organization (WHO) targets a more stringent standard of 10 μg/m3. In 2019, Philadelphia’s average annual PM2.5 level of 10.3 μg/m3 fell between these two standards, meeting the EPA target but exceeding the WHO standard. Importantly, health experts stress that no level of PM2.5 exposure has been shown to be free of health impacts.3
Philadelphia annual air quality index (AQI) levels have gradually improved since 1980. A snapshot of these improvements is clearly represented by looking at data on the year of each new decade. In 1980, 156 days were classified in the US AQI “unhealthy” category, dropping to 90 unhealthy days in 1990, 29 unhealthy days in 2000, and 10 unhealthy days in 2018.1
2019 was an off-trend year for PM2.5 as compared to the year prior, 2018. In 2019 Philadelphia’s average annual PM2.5 level increased 12.9%, from a concentration level of 9.3 μg/m3 to 10.5 μg/m3. This increase is relatively subtle, however, and may not be indicative of a worsening air quality trend.
Other US air quality index criteria pollutants, such as CO, SO2, and NO2 have been in attainment since at least 2000, with overall year-over-year improvements.
Air quality improvements in the city are likely attributable to increasingly tight regulations and the shuttering of Philadelphia's largest stationary emission source, the Philadelphia Energy Solutions refining complex. A gradual shift towards cleaner energy and transportation is likely to be another factor.4
Air pollution sources are generally classified into three primary categories: mobile sources (motor vehicles, airplanes, and locomotives), stationary sources (power plants, oil refineries, and factories) and area sources (construction, agriculture, and domestic wood burning).
Mobile emission sources are the largest contributor to Philadelphia’s unhealthy air quality.5 This is common in U.S. cities, where stationary sources are relatively few and far removed from city centers, and ownership of motor vehicles is relatively high.
While mobile sources are the greatest pollution contributors, they also offer the greatest opportunity for improving air quality. Growing the city’s share of electric and hybrid vehicles on the road as well as making public transportation and green transportation (like walking and biking) more accessible and attractive could all help significantly alleviate the city of its ozone challenges.
Currently, Pennsylvania lags behind neighboring states, such as New York, New Jersey, and Maryland, for electric vehicle ownership.6 In the state’s 2019 Climate Action Plan, transitioning more residents to electric vehicles is a stated priority.
The Philadelphia Energy Solutions refining complex has long been the city’s largest stationary emission source.4 The refinery’s approximately 470,000 pounds of annual emissions are estimated to have contributed to roughly 9% of the city’s PM2.5 emissions and 20% of the city's greenhouse gases.
It is thought that carcinogenic emissions from this refinery have played a role in Philadelphia’s cancer rate, which remains the highest of any large city in the country, as well as in Philadelphia's asthma hospitalization rate, which is three times the state average.
On June 21, 2019, a catastrophic fire caused irreparable damage to the complex, shuttering the facility permanently. Experts are hopeful that its closure will alleviate Philadelphia of significant levels of smog and unhealthy air pollution.
+ Article Resources
 City of Philadelphia Department of Public Health Air Management Services. (2018). Philadelphia’s air quality report 2018.
 American Lung Association. (2019). State of the air – 2019.
 World Health Organization. (2020). Air quality guidelines – global update 2005.
 Maykuth A. (2019, December 26). South Philly refinery, a big polluter, shut down 6 months ago. So, do we have cleaner air?
 Clean Air Council. (2020) Philadelphia’s air pollution sources and steps to attaining federal ambient air quality standards.
 McDaniel J. (2019, October 1). Electric cars offer ‘guilt-free driving’ and aid the climate. So why doesn’t Pennsylvania have more?