PurpleAir sensors measure airborne particulate matter (PM). Particulate matter describes solid particles suspended in air including dust, smoke, and other organic and inorganic particles. PurpleAir sensors use laser particle counters to count the number of particles by particle sizes 0.3, 0.5, 1, 2.5, 5, and 10 μm, and uses the count data to calculate mass concentrations of PM1.0, PM2.5, and PM10.

PurpleAir sensors use laser counters to measure particulate matter in real time. A laser counter uses a fan to draw a sample of air past a laser beam. Any particles in the air will reflect some light from the laser beam onto a detection plate, like dust shimmering in a sunbeam. The reflection is measured as a pulse by the detection plate and the length of the pulse determines the size of the particle and the number of pulses determines the particle count. The PM1.0, PM2.5, and PM10 mass concentrations are calculated from these particle counts.

PurpleAir sensors are used by a wide variety of individuals and groups from government air districts, school district, and universities to industrial and commercial use to home enthusiasts and concerned citizens.

There are two major difference for PurpleAir sensors when being compared to regulatory sensors, (1) the method of measuring particulate matter and (2) the averaging time of the data collected.

Methods:

PurpleAir sensors use a laser particle counter to count the number of airborne particulate matter by size everything second. That count data is used to calculate a mass concentration assuming an average particle density in an algorithm developed by the laser counter manufacturer, Plantower. They must use an average density because not all PM of a particular size is made of the same stuff. For instances, PM2.5 from wildfire smoke will have a different density than PM2.5 from dust blowing off a gravel pit. This means the mass concentration reported by a PurpleAir sensor can vary depending on the specific composition of PM for a given area. Thus making the sensors appear to "read high". So far, 2 different research groups have completes studies for their areas to create conversion factors for PurpleAir specific to the composition of the air shed (AQandU and LRAPA on the PurpleAir map).

For reference, federal reference sensors typically measure mass concentration of PM directly. This method is expensive, difficult to install, requires a specialist to maintain the sensor, and report on an hourly scale. Because of this many cities have a limited number of these sensors (or none at all) and it's not feasible for the general public have their own.

Averaging Time:

PurpleAir uses the AQI breakpoints established by the US EPA to convert the mass concentration into the AQI published on the PurpleAir map. However, the most regulatory groups report AQI as a 24-hour average that get updated every hour or so. If you look at PM on a website like AirNow, a PM2.5 AQI of 150 means the average AQI in the last 24-hours was 150.

PurpleAir sensors use laser particle counters to count the number of particle sizes from 0.3um up to 10 um that get converted into a mass concentration (ug/m3) and report AQI in 80-second averages that get updated every 80 seconds. On PurpleAir, a PM2.5 AQI of 150 means the average AQI in the last 80 seconds was 150. Since air quality can fluctuate greatly throughout the day, the real time PurpleAir AQI reading may appear "high" when compared to 24-hour averaged AQI data.

If you want to compare 24-hour averaged AirNow data with 24-hour averaged PurpleAir data you can look at longer term averages on the PurpleAir map in the sensor icon pop-up box or checking the "Show Rings (Averages)" in the Map Data Layer box in the lower left hand corner of the map.

Each ring represents the averages:

Center of the circle = Real time averages
1st ring = Short Term averages
2nd ring = 30 minute averages
3rd ring = 1 hour averages
4th ring = 6 hour averages
5th ring = 24 hour averages
6th ring = 1 week averages

The PA-II and PA-II-SD both have WiFi capabilities and come with 2 laser counters. The difference is that the PA-II-SD comes with an internal microSD card reader and real time clock that logs the data and tracks time with or without a WiFi connect. 

Currently, you must remove the microSD card from the sensor and plug it into your computer to read and analyze the data. It is not possible to upload the SD card data to the PurpleAir map. The PA-II-SD is intended for places that do not have access to WiFi or have intermittent WiFi.

The sensor housing on the PA-II and PA-II-SD is designed to protect the device from the elements while allowing air to flow freely past the two laser counters. We recommend installing in a location high enough so that water splash or snow cannot get into the underside of the sensor.

All PurpleAir sensors can be used indoors. Our most popular sensor is the PA-II and many people use the PA-II sensor as an indoor sensor. This sensor can be mounted on the wall and contain dual laser counters so you can compare the data from each laser counter to confirm your sensor is reporting correctly. Additionally, we have an indoor specific sensor, the PA-I-indoor. It is designed to sit on a flat surface like a countertop or desk and contains a LED light on top that illuminates the color of the current AQI (green, yellow, orange, red, purple, and maroon).

We do not recommend a regular cleaning schedule for PurpleAir sensors. "If it ain't broke, don't fix it"

If one of the laser counters is not reporting as expect we do recommend that you try to clean out any debris, insects, or spiders that may have made their way inside of the laser counter. You can use a shop vac and placing it on the bottom of the sensor for 2-3 minutes or try clearing out the laser counter with compressed air. Focus on the 4 vertical holes on each laser counter.

The laser counters used in PurpleAir sensors come factory calibrated. It is not possible to calibrate the laser counters post-production. If you suspect your sensor might have a laser counter misreporting you can try cleaning the laser counters with a vacuum, shop vac, or canned compressed air.

Before shipment, we verify that every sensor is reporting data that are consistent from sensor to sensor during tests in a smoke chamber.

It is possible that some debris, an insect or spider got into one of the laser counters in your sensor. To clean out laser counter you can use a shop vac and placing it on the bottom of the sensor for 2-3 minutes or try clearing out the laser counter with canned compressed air. Focus on the 4 vertical holes on each laser counter. 

We do not recommend a regular cleaning schedule of the sensors.

We do not recommend covering the base of your sensor with any material. This will impact the air flow and ability for the sensor to properly measure particulate matter.

We have heard of a number of individuals running their sensors with solar power. However, we personally have not tested running PurpleAir sensors with a solar power in house. That being said it seems reasonable that solar panels between 10 W and 15 W should be adequate to power a battery pack to run a PurpleAir sensor.  How quickly that battery pack recharges is situationally dependent and might take some experimenting on your part to fit the seasonal sun conditions. 

Power draw: The sensor uses 180mA (milliamp), about 1 Watt.  We have experimented with a 20Ah battery pack and it kept the sensor running for about 4 days.

Every icon on the PurpleAir map represents a public PurpleAir sensor and the color indicates the real time PM2.5 reading on the US EPA Air Quality Index scale. The sensors with no outline are registered as outdoor sensors and the sensors with black rings are registered as indoor sensors.

When clicking a sensor icon, two informative boxes display. One shows the sensor information and averages over the last week.

The other shows a graphical chart of readings from channel A and B over the last week.

The default display on the PurpleAir map is United States Environmental Protection Agency (EPA) Air Quality Index (AQI) scale for PM2.5. The AQI allows comparison for different pollutants with an easy to visualize color scheme. The air goes from good green air to yellow to orange to red to purple air, or even more hazardous maroon air. The graphs give further information on different counts, relative weights and sizes of particles in the air.

When you click on a sensor icon on the PurpleAir map the graph will populate with 10 minute average data for each laser counter for that sensor. You can add more sensors to the same graph by selecting additional sensor icons.

You can make individual sensor channels visible or not by clicking on the name in legend. Visible channels are black in the legend. Hidden channels are gray in the legend.

You can select the data type displayed on the PurpleAir map using the Map Data Layer drop down menu.

The default setting on the PurpleAir map is the US EPA PM2.5 AQI calculated from the raw PM2.5 concentration reported by PurpleAir sensors. You have the option to can choice to apply LRAPA or AQandU conversion to PM2.5 data on the PurpleAir map.

Purple Air uses a laser particle counter to count particulate matter (PM) suspended in the air. This counting process can detect particle sizes from 0.3 μm up to 10 μm. To convert the particle count to a mass concentration (μg/m3), laser particle counters must assume an average particle density. They must use an average because not all PM of a particular size is made of the same stuff. For instances, PM2.5 from wildfire smoke will have a different density than PM2.5 from dust blowing off a gravel pit. This means the mass concentration reported by a PurpleAir sensor vary depending on the specific composition of PM for a given area. The AQ&U conversion factor was developed by the University of Utah to convert the mass concentration data measured by PurpleAir sensors to best fit the PM composition of wintertime air in Salt Lake City. 

Salt Lake City is a large urban area with a variety of industrial operations within a mountain valley. Individuals living in comparable environments could consider using the AQ&U conversion factor. As more research becomes available for different areas, PurpleAir will post additional conversion factors.

In the PurpleAir legend there are checkboxes for "Outside Sensors", "Inside Sensors", and "Show My Sensors". Check the boxes of the sensors you want to be visible on the PurpleAir map.

Outdoor sensor icons have no outline. Indoor sensor icons have a bold outline.

If you prefer to see the sensor averages to display on the map dots, check “Show Rings” on the map controller.   The rings give a visual display of the average historic readings, showing the same averages you see when clicking a specific sensor.

Each ring represents an average for a time range:

Center of the circle = Real time averages

1st ring = Short Term averages

2nd ring = 30 minute averages

3rd ring = 1 hour averages

4th ring = 6 hour averages

5th ring = 24 hour averages

6th ring = 1 week average

At this time, you can login to the PurpleAir website with a Google account. If you set the Owner's Email to a Google account when registering the sensor then you can login to the PurpleAir map this enable you to use the "Show My Sensors" checkbox in the map legend to view your PurpleAir sensors. This can be especially useful if you have registered your sensor as private

To login:

1. Click Login in the upper righthand corner of the PurpleAir map
2. Select the Google account set as the Owner's Email for your PurpleAir sensor(s)
3. Enter your Google account password

To change the Owner's Email on a PurpleAir sensor that was already registered send a request here.

There are 2 ways to view your private PurpleAir sensors on the PurpleAir map

1. Login to the PurpleAir map with a Google account set as the Owner's Email for the private sensors
2. Use the link provided in the registration email to view a private sensor

If you would like to update the Owner's Email on your sensor send a request here.

At this time, we don't have an easy way to get sensors outside of the PurpleAir network reporting to the PurpleAir map.

PurpleAir PA-II and PA-II-SD sensors contain 2 laser particle counters that measure the real time particulate matter and report as Channel A and Channel B. If the values being reported for the 2 laser particle counters drifts apart our system may "downgrade" one of the channels. The downgraded channel will no longer be used in the data average and will be grayed out in the graph's legend. You can still view the downgraded channel on the graph by clicking on the downgraded name in the graph's legend. 

1. Find the sensor you wish to order on the air quality sensors page
2. Enter the quantity in the box
3. Select Add to Cart
4. Select Check Out
5. Enter your email and shipping information and select Continue to Shipping Method
6. Select shipping method
7. Enter preferred payment method
8. Select Complete Payment to finalize your order.

Any order confirmation email will sent to the email address entered for the order. A shipping confirmation email will be sent once your order ships.

You can request an invoice or quote by sending us a message on our contact form

Yes, we do! Please contact us using our contact form if you need to complete a purchase using a purchase order.

At PurpleAir, we do our best to process orders in 1-2 business days of the purchase date. However, this time can vary due to stock availability, weekends (Saturday and Sunday), or national holidays.

For current estimated order fulfillment time send us a message here

Within USA:
USPS Priority Mail delivers in 1 to 3 business days.

Within Canada:
USPS Priority Mail International delivers in 6 to 10 business days.

DHL International delivers in 1 to 3 business days. Actual number of days may vary based on origin, destination, and customs delays

International Shipping:
DHL International delivers in 1 to 3 business days. Actual number of days may vary based on origin, destination, and customs delays.

Contact us here with the order number and updated shipping address as soon as possible and we can update your order.

Yes! We ship with USPS International and DHL International. 

Tariffs/customs duties are paid by buyer and due at delivery. 

Firmware version 4.02 and later

1. On a WiFi enable device open the list of available WiFi networks.

2. Connect to the sensor's network "PurpleAir-xxxx". The xxxx is a 2-4 dight code specific to your sensor.

   Important: If your sensor network name is "AirMonitor_xxxx" you will need to go to www.purpleair.com/configure to configure WiFi on your sensor.

3. Depending on your operating system or device you may get a pop-up window or a message to sign into the network. If you get a message to sign into the network, press it to make the pop-up window appear.
4. The pop-up window will list available WiFi networks.
5. Choose the WiFi network you would like the sensor to use, enter the password, and click save. A hidden WiFi network can be entered by selecting the option at the bottom of the list.
6. The WiFi status bar will turn green once your PurpleAir sensor is connected to WiFi and transmitting data.

Firmware version 3.00 and earlier

1. On a computer, tablet, or smartphone open the PurpleAir configuration page in Google Chrome and leave it open

2. Go to the list of available WiFi networks and look for the PurpleAir sensor network, AirMonitor_xxxx

3. Connect to the AirMonitor_xxxx network

4. Go to the PurpleAir configuration page opened in step 1 and click on the "Connect to Sensor" button

5. Select the desired WiFi network from the list

6. Enter the WiFi network password  and click Save

7. Your sensor should be online

If it was successful the sensor data should become visible in the web browser and the AirMonitor_xxxx network should no longer be visible.

Cannot see the AirMonitor_xxxx network

- Make sure the sensor is receiving power by checking that the power outlet is working and the power supply is securely connected to the power outlet and sensor then check for a dim red glow underneath the sensor housing.
- If the sensor is in range of a WiFi network it was previously configured to you will need to turn off that WiFi network or take the sensor out of range of that WiFi network to make the AirMonitor_xxxx network visible again.

Cannot connect to AirMonitor_xxxx network

- Sometimes computers, tablets, or smartphones will not connect to the AirMonitor_xxxx because this network does not reach the internet. This is a security feature on some devices. If a pop-up alert appears you may need to select trust the network or "connect anyways to the network, or repeat attempts to connect to the AirMonitor_xxxx on the same device.

WiFi network name is incomplete or not on the list after clicking "Connect to Sensor"

- Make sure your PurpleAir sensor is near the wireless router to ensure the sensor is within range of the WiFi network.
- PurpleAir sensors can only be configured to 2.4GHz networks. Any other networks will not be visible.
- If the WiFi network name contains an apostrophe (Example: John's WiFi) you will need to manually configure your sensor to the WiFi network.

Sensor will not connect to the WiFi or is not showing up on the PurpleAir map

- PurpleAir sensors must be configured to a WiFi network and registered to be visible on the PurpleAir map. Make sure your sensor was successfully registered.
- PurpleAir sensors work on WPA2 Pre-Shared Key networks. If there is any kind of secondary authentication (like clicking on a button in a web page) to connect to the WiFi network, the sensor would need to be whitelisted on the router.
- Check the password for 2.4GHz WiFi network by logging in to the router to double check your password for your 2.4GHz WiFi network.

PurpleAir sensors use a WPA2 pre-shared key. If the desired network requires any secondary authentication (like clicking on a button in a web page or login with a username and password), the devices would need to be whitelisted on the router after being configured to the WiFi network.

The list of fully qualified domain (FQDN) names for PurpleAir sensors are:
www.purpleair.com
update.purpleair.org
update.purpleair.com
api.thingspeak.com
sensors-ingest.wunderground.com
Pool.ntp.org
www.googleapis.com

Ports used by PurpleAir sensors:
Port 80 for HTTP
Port 443 for HTTPS
DNS: 53
NTP: 123

There is not a button to reset the WiFi network connection.  To make the sensor network, AirMonitor_xxxx, visible again you will need to turn off the WiFi network or take the sensor is out of range of the WiFi network the sensor is currently configured to.  Once sensor network is broadcasting again, you will be able to connect it to a different network. Just make sure the WiFi network it is currently installed on remains out of range/offline until it is successfully configured to the new network.

The registration form can be used to register a new PurpleAir sensor or update registration details on a previously registered PurpleAir sensor. A registration confirmation email will be sent to the Associated Email and Owner's Email indicated on the registration form.

Individual registration fields are described below.

Device-ID (MAC address): A unique code for every sensor the is printed on the sensor sticker or listed in the shipping confirmation email.

Associated Email: The email address used by the buyer to complete the purchase of the sensor. This email must be used to register the sensor. Look for a green "Looking good: Device-Id and Associated Email are related..." box on the registration form. Contact us to associate a different email address with a sensor.

Installed: Indicates whether this sensor will be installed indoors or outdoors

Location Name: The name of the sensor icon that will appear on the PurpleAir map

Visibility: Choice whether you want the sensor icon to be visible on the public PurpleAir map or only visible to the sensor owner.

Map Location: Drag and drop the red marker on the map to select a location for the sensor icon to appear on the PurpleAir map. If no location is set the sensor icon will be placed at the lat/long "0/0", which is off the west coast of Africa.

Data Processor #1: By default sensor data will be sent to Weather Underground and used in WU air quality report. Use the drop down menu to select another 3rd party service to receive sensor data or select None.

Data Processor #2: Use the drop down menu to select an additional 3rd party service to receive sensor data or select None.

Owner's Name: The name of the owner of the PurpleAir sensor

Owner's Email: References the physical owner of the sensor, which can be the same or different as the Associated Email. The Owner's Email can be any email address, but must be a Google account if you want to be able to login to the PurpleAir map and use the "Show My Sensors" checkbox. Once the Owner's Email is set you must contact us if you'd like to change the Owner's Email.

SMS Alert Phone Number: The phone number of the owner of the PurpleAir sensor.

You can update registration details by resubmitting the registration form. You must enter the same Associated Email and Owner's Email that was entered when original registration. Any other details entered on the registration form will be used to update the PurpleAir map.

Moving a PurpleAir sensor to a new location:

Before moving the sensor to a new location or changing it from an indoor to outdoor sensor, contact us to request the data gathered to date be archived to the physical location and the sensor reset to gather fresh data in the new location. Once the data archive is confirmed by our team, the Registration form can then be resubmitted with the new location information entered.

PurpleAir sensor owners have the option to select 2 additional locations to send their PurpleAir sensor data. By default PurpleAir sensors will send sensor data to Weather Underground's air quality report.

None: PurpleAir sensor data will not be sent to an additional location

Weather Underground:

Check "Create new Weather Underground sensor ID"

The default setting will check the checkbox for "Create new Weather Underground sensor ID" and will send data to them through their new API that is not part of the PWS system but they are working on having the two integrated together. This API feeds the algorithms that drive their Air Quality readings and forecasts.

Un-check "Create new Weather Underground sensor ID"

When you un-check the checkbox for "Create new Weather Underground sensor ID" the KEY3 and KEY4 fields will become visible. You can add the station id (KEY3) and station key (KEY4) to display the sensor data on a PWS, which will not share the data through the API used to create the Weather Underground air quality report. Sending sensor data to a PWS essentially make the air quality data private unless someone looks specifically at that PWS.

Custom: Any HTTP server of your choice

KEY3 - Should contain the full server address including “http://” or “https://” and any querystring
KEY4 (optional) - Should contain any header to be included in the request. For example “SomeKey: SomeValue”
METHOD - The Http method being GET, POST or PUT

- Find a location with easy access to a power outlet and is within range of the WiFi network

- You can mount the sensor using either cable ties or a screw

- Find a location with easy access to a power outlet

- Mount the sensor away from any foliage that would increase the chances of inscets or spiders getting inside of the laser counters. 

- The sensor is designed to lay flat on a hard surface like a counter top or desk. 

The simplest way to download the data is using the PurpleAir Sensor List available at https://www.purpleair.com/sensorlist. This page provides an easy to use interface to download data based on a date range.  

***You will need to use a Chrome browser to download any data.***

- Find and mark the sensor/s in the list you want to download - use CTRL + F to quickly search by sensor name
- Return to the top of the page and enter the desired date range, then click Download Selected

If you want to download data from a private sensor the Owner's Email for the sensor must be a Google account and you must login with that Google account at the top of the Sensor List. To update the Owner's Email on a sensor that was previously registered contact us.

Make sure you are using Google Chrome as your web browser to download data and turn off any pop-up blockers and ad blockers. 

PurpleAir sensor data is stored in the ThingSpeak data cloud. ThingSpeak stores the data in "channels" that have a limit of 8 data fields per channel. PA-II and PA-II-SD sensors contain 2 laser counters that report independently, hence Channel A and Channel B. PA-I-Indoor sensors contain 1 laser counter, so only report on one channel, Channel A. Each channel is further divided into 2 data sets, Primary and Secondary, due to the data field limits per ThingSpeak channel. Below are the header descriptions for Channel A Primary, Channel A Secondary, Channel B Primary, and Channel B Secondary data files.

Channel A Primary:

created_at: Timestamp of data posting to ThingSpeak (created by ThingSpeak)
entry_id: row number relative to all data channel A primary data (created by ThingSpeak)
PM1.0_CF_ATM_ug/m3: mass concentration calculated from count data for particle sizes ~0.3um to ~1.0um for “atmospheric” particles (From Plantower 5003/1003)
PM2.5_CF_ATM_ug/m3: mass concentration calculated from count data for particle sizes ~0.3um to ~2.5um for “atmospheric” particles (From Plantower 5003/1003)
PM10.0_CF_ATM_ug/m3: mass concentration calculated from count data for particle sizes ~0.3um to ~10um for “atmospheric” particles (From Plantower 5003/1003)
UptimeMinutes: the amount time the unit CPU has been running since it was powered up (From ESP8266 WiFi chip)
ADC: Voltage (From ESP8266 WiFi chip)
Tempertautre_F: Temperature inside of the sensor housing in Fahrenheit. On average, this is 8F higher than ambient conditions. (From BME280)
Humidity_%: Relative humidity inside of the sensor housing as a percentage. On average, this is 4% lower than ambient conditions (From BME280)
PM2.5_CF_1_ug/m3: mass concentration calculated from count data for particle sizes ~0.3um to ~2.5um for “standard” particles (From Plantower 5003/1003)

Channel A Secondary:

created_at: Timestamp of data posting to ThingSpeak (created by ThingSpeak)
entry_id: row number relative to all data channel A primary data (created by ThingSpeak)
0.3um/dl: aerodynamic diameter of >0.3 micrometer particle counts per deciliter of air
0.5um/dl: aerodynamic diameter of >0.5 micrometer particle counts per deciliter of air (From Plantower 5003/1003)
1.0um/dl: aerodynamic diameter of >1.0 micrometer particle counts per deciliter of air (From Plantower 5003/1003)
2.5um/dl: aerodynamic diameter of >2.5 micrometer particle counts per deciliter of air (From Plantower 5003/1003)
5.0um/dl: aerodynamic diameter of >5.0 micrometer particle counts per deciliter of air  (From Plantower 5003/1003)
10.0um/dl: aerodynamic diameter of >10.0 micrometer particle counts per deciliter of air (From Plantower 5003/1003)
PM1.0_CF_1_ug/m3: mass concentration calculated from count data for particle sizes 0.3um to ~1.0um for “standard” particles (From Plantower 5003/1003)
PM10.0_CF_1_ug/m3: mass concentration calculated from count data for particle sizes ~0.3um to ~10um for “standard” particles (From Plantower 5003/1003)

Channel B Primary:

created_at: Timestamp of data posting to ThingSpeak (created by ThingSpeak)
entry_id: row number relative to all data channel A primary data (created by ThingSpeak)
PM1.0_CF_ATM_ug/m3: mass concentration calculated from count data for particle sizes ~0.3um to ~1.0um for “atmospheric” particles (From Plantower 5003/1003)
PM2.5_CF_ATM_ug/m3: mass concentration calculated from count data for particle sizes ~0.3um to ~2.5um for “atmospheric” particles (From Plantower 5003/1003)
PM10.0_CF_ATM_ug/m3: mass concentration calculated from count data for particle sizes ~0.3um to ~10um for “atmospheric” particles (From Plantower 5003/1003)
UptimeMinutes: the amount time the unit CPU has been running since it was powered up
RSSI_dbm: WiFi strength (From ESP8266 WiFi chip)
Pressure_hpa: Pressure inside of the sensor housing in hectopascal. (From BME280)
Blank: No Data
PM2.5_CF_1_ug/m3: mass concentration calculated from count data for particle sizes ~0.3um to ~2.5um for “standard” particles (From Plantower 5003/1003)

Channel B Secondary:

created_at: Timestamp of data posting to ThingSpeak (created by ThingSpeak)
entry_id: row number relative to all data channel A primary data (created by ThingSpeak)
0.3um/dl: aerodynamic diameter of >0.3 micrometer particle counts per deciliter of air
0.5um/dl: aerodynamic diameter of >0.5 micrometer particle counts per deciliter of air (From Plantower 5003/1003)
1.0um/dl: aerodynamic diameter of >1.0 micrometer particle counts per deciliter of air (From Plantower 5003/1003)
2.5um/dl: aerodynamic diameter of >2.5 micrometer particle counts per deciliter of air (From Plantower 5003/1003)
5.0um/dl: aerodynamic diameter of >5.0 micrometer particle counts per deciliter of air (From Plantower 5003/1003)
10.0um/dl: aerodynamic diameter of >10.0 micrometer particle counts per deciliter of air (From Plantower 5003/1003)
PM1.0_CF_1_ug/m3: mass concentration calculated from count data for particle sizes 0.3um to ~1.0um for “standard” particles (From Plantower 5003/1003)
PM10.0_CF_1_ug/m3: mass concentration calculated from count data for particle sizes ~0.3um to ~10um for “standard” particles (From Plantower 5003/1003)

PurpleAir sensor data is stored in the ThingSpeak data cloud. ThingSpeak stores the data in "channels" that have a limit of 8 data fields per channel. PA-II and PA-II-SD sensors contain 2 laser counters that report independently, hence Channel A and Channel B. PA-I-Indoor sensors contain 1 laser counter, so only report one channel, Channel A. Each channel is further divided into 2 data sets, Primary and Secondary, due to the data field limits per ThingSpeak channel. Below are the header descriptions for Channel A Primary, Channel A Secondary, Channel B Primary, and Channel B Secondary data files.

The CF_ATM and CF_1 values are calculated from the particle count data with a proprietary algorithm developed by the PMS5003 laser counter manufacturer, PlanTower. The specifics of the calculation are not available to the public (or us for that matter). However, to convert the particle count data (um/dl) to a mass concentration (ug/m3) they must use an average particle density. They do provide 2 different mass concentration conversion options; CF_1 uses the "average particle density" for indoor particulate matter and CF_ATM uses the "average particle density" for outdoor particulate matter. Depending on the density of the particles you are measuring the sensor could appear to read "high" or "low". Some groups have developed conversion factors to convert the data from the sensor to match the unique average particle density within their airshed. 

PurpleAir provides access to our real time data in a JSON format. This format allows developers to access current data for all sensors or a subset of sensors.

There are two ways to access the JSON data:

All sensors: https://www.purpleair.com/json
One entry: https://www.purpleair.com/json?show=<id> where ID is the “ID” of the sensor you want (in the case of dual laser where ParentID is “null”).

If you want to access data from a private sensor the Owner's Email for the sensor must be a Google account and you must login with that Google account on purpleair.com before navigating to purpleair.com/json. To update the Owner's Email on a sensor that was previously registered contact us.

NOTE: Please limit multiple threaded applications to a few threads at any time to reduce load on purpleair.com or thingspeak.com servers. If you do not limit the amount of threads, you may be blocked on the firewall.

The following is a list of the fields and a description of their values contained in the JSON data:

"ID":1234, // PurpleAir sensor ID
"ParentID":null, // The PurpleAir sensor ID of the "parent" entry in the case of Channel B
"THINGSPEAK_PRIMARY_ID":"1234", // The Thingspeak channel ID for primary data of this sensor
"THINGSPEAK_PRIMARY_ID_READ_KEY":"XXXX", // The Thingspeak read key for primary data of this sensor
"Label":"name", // The "name" that appears on the map for this sensor
"Lat":null, // Latitude position info
"Lon":null, // Longitude position info
"PM2_5Value":"1.07", // Current PM2.5 value (based on the
"State":null,  // Unused variable
"Type":"TYPE",  // Sensor type (PMS5003, PMS1003, BME280 etc)
"Hidden":"true", // Hide from public view on map: true/false
"Flag":null, // Data flagged for unusually high readings
"DEVICE_BRIGHTNESS":"1", // LED brightness (if hardware is present)
"isOwner":1, // Currently logged in user is the sensor owner
"A_H":null, // true if the sensor output has been downgraded or marked for attention due to suspected hardware issues
"temp_f":"xx",  // Current temperature in F
"humidity":"xx", // Current humidity in %
"pressure":"xx", // Current pressure in Millibars
"AGE":29831, // Sensor data age (when data was last received) in minutes
"THINGSPEAK_SECONDARY_ID":"1234", // The Thingspeak channel ID for secondary data of this sensor
"THINGSPEAK_SECONDARY_ID_READ_KEY":"XXXX", // The Thingspeak read key for secondary data of this sensor
"LastSeen":1490309930, // Last seen data time stamp in UTC
"Version":"2.47c", // Current version of sensor firmware
"LastUpdateCheck":1490308331, // Last update checked at time stamp in UTC
"Uptime":"5210", // Sensor uptime in seconds
"RSSI":"-68", // Sensor's WiFi signal strength in dBm

"Stats": // Statistics for PM2.5

"{
\"v\":1.07, // Real time or current PM2.5 Value
\"v1\":1.3988595758168765, // Short term (10 minute average)
\"v2\":10.938131480857114, // 30 minute average
\"v3\":15.028685608345926, // 1 hour average
\"v4\":6.290537580116773, // 6 hour average
\"v5\":1.8393146177050788, // 24 hour average
\"v6\":0.27522764912064507, // One week average
\"pm\":1.07, // Real time or current PM2.5 Value
\"lastModified\":1490309930933, // Last modified time stamp for calculated average statistics
\"timeSinceModified\":69290 // Time between last two readings in milliseconds
}"
}

Another way to get the data is to use ThingSpeak.com and to do this, you will need the API Key and channelID. These two pieces of data are available from PurpleAir’s JSON.

More info on using ThingSpeak’s API is here: https://www.mathworks.com/help/thingspeak/rest-api.html

NOTE: Please limit multiple threaded applications to a few threads at any time to reduce load on purpleair.com or thingspeak.com servers. If you do not limit the amount of threads, you may be blocked on the firewall.

We use tweezers to access the SD cards.  They are not meant to be accessed frequently so they are a bit harder to get to.  Also when you replace the SD card or powering on when not connected to WiFi you will want to make sure there is a blue LED light that flickers next to the SD card from time to time (the logging period). If it flickers three times, the SD card itself was not loaded properly and not logging data. It is helpful to have them connected to WiFi to make sure they are logging correctly, but realize this may not be available.  In order to get any future firmwares update you will need to be able to connect the sensor to a network as well.

The SD Card version of the PA-II (PA-II-SD) has a built in real time clock and OPENLOG serial logger. The SD card contains data in CSV format with the following headers:

UTCDateTime, mac_address, firmware_ver, hardware, current_temp_f, current_humidity, current_dewpoint_f, pressure, adc, mem, rssi, uptime, pm1_0_atm, pm2_5_atm, pm10_0_atm, pm1_0_cf_1, pm2_5_cf_1, pm10_0_cf_1, p_0_3_um, p_0_5_um, p_1_0_um, p_2_5_um, p_5_0_um, p_10_0_um, pm1_0_atm_b, pm2_5_atm_b, pm10_0_atm_b, pm1_0_cf_1_b, pm2_5_cf_1_b, pm10_0_cf_1_b, p_0_3_um_b, p_0_5_um_b, p_1_0_um_b, p_2_5_um_b, p_5_0_um_b, p_10_0_um_b

Firmware version 4.02 - Header Error

PA-II-SD sensors running firmware version 4.02 contain a header error on the SD card. To fix, open the csv file and find the header "hardwareversion". You will need to delete this header and move all following header columns to the left one. The "gas" header in the last column should now line up with the last column of data.

Header Descriptions

UTCDateTime: The Date and time derived from the Real Time Clock and synced with NTP where possible (in UTC).

Mac_address: The MAC address of the WiFi module on the sensor (used as an ID for the unit).

Firmware_ver: Firmware version of the control board.

Hardware: Hardware the control board has detected.

current_temp_f: Current temperature in F.

Current_humidity: Current Humidity in %.

Current_dewpoint_f: Calculated dew point in F.

Pressure: Current pressure in millibars.

Adc: The voltage reading on the analog input of the control board.

Mem: Free HEAP memory on the control board.

Rssi: WiFi signal strength in dBm

Uptime: Firmware uptime in seconds.

Pm1_0_atm: Channel A ATM PM1.0 particulate mass in ug/m3

Pm2_5_atm: Channel A ATM PM2.5 particulate mass in ug/m3

Pm10_0_atm: Channel A ATM PM10.0 particulate mass in ug/m3

Pm1_0_cf_1: Channel A CF=1 PM1.0 particulate mass in ug/m3

Pm2_5_cf_1: Channel A CF=1 PM2.5 particulate mass in ug/m3

Pm10_0_cf_1: Channel A CF=1 PM10.0 particulate mass in ug/m3

P_0_3_um: Channel A 0.3 micrometer particle counts per deciliter of air

P_0_5_um: Channel A 0.5 micrometer particle counts per deciliter of air

P_1_0_um: Channel A 1.0 micrometer particle counts per deciliter of air

P_2_5_um: Channel A 2.5 micrometer particle counts per deciliter of air

P_5_0_um: Channel A 5.0 micrometer particle counts per deciliter of air

P_10_0_um: Channel A 10.0 micrometer particle counts per deciliter of air

Pm1_0_atm_b: Channel B ATM PM1.0 particulate mass in ug/m3.

Pm2_5_atm_b: Channel B ATM PM2.5 particulate mass in ug/m3

Pm10_0_atm_b: Channel B ATM PM10.0 particulate mass in ug/m3

Pm1_0_cf_1_b: Channel B CF=1 PM1.0 particulate mass in ug/m3

Pm2_5_cf_1_b: Channel B CF=1 PM2.5 particulate mass in ug/m3

Pm10_0_cf_1_b: Channel B CF=1 PM10.0 particulate mass in ug/m3

P_0_3_um_b: Channel B 0.3 micrometer particle counts per deciliter of air

P_0_5_um_b: Channel B 0.5 micrometer particle counts per deciliter of air

P_1_0_um_b: Channel B 1.0 micrometer particle counts per deciliter of air

P_2_5_um_b: Channel B 2.5 micrometer particle counts per deciliter of air

P_5_0_um_b: Channel B 5.0 micrometer particle counts per deciliter of air

P_10_0_um_b: Channel B 10.0 micrometer particle counts per deciliter of air

PA-II NOTES:

Each sensor contains two identical laser counters, hence channel A and B. If these two channels do not agree to some extent then there is something wrong with one or both channels.

Plantower PMS sensor notes:

ATM is "atmospheric", meant to be used for outdoor applications

CF=1 is meant to be used for indoor or controlled environment applications

However, PurpleAir uses CF=1 values on the map. This value is lower than the ATM value in higher measured concentrations.

At this time, when the sensor is out of network range and recording to the SD, the data is solely stored on the SD card.  When you come back into network range, the data that was logged when offline is not synced up to the cloud. The SD card would have to be pulled to extract that data. 

It is possible to swap out the SD card that comes with the sensor.  The card must be formatted for FAT32 - 

Mac Tutorial: https://www.youtube.com/watch?v=DA48hcfZv0g   
Windows 10 Tutorial: https://www.youtube.com/watch?v=Vd3OOwOzDp8