Best tools to track AQI in Philadelphia

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The air quality in Philadelphia has been in constant flux this week.

After late Wednesday and early Thursday morning brought Philly's worst air quality index (AQI) readings — topping 400, firmly in the "hazardous" range — the haze dissipated somewhat during the day to merely "unhealthy."

That pattern of AQI rising overnight and dropping during the day (see chart below) happens because of the way the heat from the sun affects the air, according to National Weather Service Philadelphia/Mount Holly meteorologist Sarah Johnson.

"I suspect one of the reasons is during the day we typically see mixing between lower levels of the atmosphere and middle levels of the atmosphere," Johnson said, which helps with dispersion.

Generally, the main weather pattern responsible for bringing the smoke to the Philadelphia area is expected to shift west, Johnson told Billy Penn, noting that's not an actual NWS forecast. (The EPA is the federal agency that takes the lead in making air quality predictions, she clarified.)

According to the state Dept. of Environmental Protection, things are looking up.

"Over the weekend, expect increasing amounts of sunshine each day," said Daniel Roble, a Pa. DEP air quality program specialist, in his Thursday morning extended smoke outlook, citing a likely shift in "orientation of the plume of smoke impacting the northeastern U.S." and potential rain.

In the meantime, AQI will continue to ebb and flow. Here are some tools to help you track the air quality in your immediate vicinity.

The health department monitors Philly's air quality daily and in real-time. Philadelphians can click to view a meter tracking the city's overall AQI number, along with an explanation of the scale that indicates whether or not the reading is safe or hazardous.

Find it here: Phila.gov

This map lets you look at each of the city's seven air quality sensors and view the pollution counts in that specific area. There's no AQI reading; instead It's more detailed, showing the types of pollutants and the concentrations of each pollutant in that area.

Find it here: Phila.gov

This tracker from the EPA, which monitors air quality daily and in real-time, lets you enter your zip code to find the AQI in your area. It shows whether air is hazardous or not, who each reading is hazardous for, as well as recommendations for what to do for each reading.

You can view a color-coded map of AQI around the region, and read a fine-print air quality forecast with information provided by the Pennsylvania Department of Environmental Protection. There is also a free app version of this tool.

Find it here: AirNow.gov | Apple App Store | Google Play

PurpleAir is a Utah-based company that sells air quality sensors, per its website. It publishes an online map that tracks AQI in real-time based on those sensors, which are all over the region — in more locations than the city's seven. The site also shows a mini forecast of how the air quality will change throughout the day.

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There is no standalone PurpleAir app, but the data is used to power an air quality layer you can turn on if you use the Google Maps app — kind of like viewing how bad traffic is in a given area, but instead with pollution.

Find it here: PurpleAir.com | Apple App Store | Google Play

AQICN is part of the World Air Quality Index, a nonprofit project powered by volunteer scientists that was started in 2007 in Beijing, per its website. It provides AQI readings that update every two hours or so, and provides readings on a city or county level. It also displays info on the specific pollutants affecting each area, along with temperature, humidity, wind, and pressure. Below the initial reading, a forecast can be found for the next four days.

Find it here: AQICN.org

If you want to get ultralocal and determine the air quality inside your home, you can buy your own air quality sensor. Most work the same as the ones used by the EPA, meaning they can pick up on five pollutants as well as temperature and humidity. They range from around $150 to several hundred dollars.