# PurpleAir

## How it Works

This page does a great job of explaining how laser optical particle counters work in detail. But, the most important things to know when deciding to use an optical particle counter like the PurpleAir is that:

1. The data the PurpleAir (and other optical counters) produce is an estimation of particulate mass concentration that relies on several assumptions for shape, diameter and density. The quality of your data will depend on those assumptions as well as environmental considerations such as humidity, light and temperature.
2. Because of the fact that optical counters rely on these assumptions, the data produced by them are not FRM or FEM certified.

That being said, there have been a number of academic studies that have quantified the performance and limitations of some of these optical sensors to help you choose which one to use depending on what you are trying to sense and what level of performance you are looking for. The EPA has an excellent summary of these studies in this table here. A higher R2 value means better performance.

Here is a study specific to PurpleAir.

## Use Cases

• PurpleAir maintains a map of every user's data from around the world. Check it out.
• A use case in Utah
• A use case in California
• This facebook group includes people who own a PurpleAir and discuss their experiences
• This blog has some dialogue about various use issues

## Suggestions for conducting particulate matter investigations

This page summarizes important considerations before starting an investigation. To add onto those, specifically in regards to air quality, here are some suggestions.

Before ordering a sensor, check out the data that is freely available to you online. Visit your state's department of environmental management website and their air quality section. With some poking around, you can find their ‘Air monitoring network plan’ which will show you the exact locations of all of their different FEM/FRM sensors and what pollutant they are measuring. This can help to identify gaps in their monitoring network that you may be interested in.

AirNow has national daily data from FEM monitors. You can search for your zip code and see the live air quality forecast. This can be used to help inform your day to day movements especially if you are an asthmatic.

You can also download data* from FRM monitors here. This is really cool because you can specify what data you want and it will generate an Excel file for you. You can then start making plots and figures to compare different time periods and locations. Check out this post which used this online EPA data to create some visualization of the monitoring in Rhode Island.

*NOTE: As mentioned earlier, the FRM data has a lag for quality assurance reasons. For example, the most current Rhode Island data is for May 2018. (It is August at the moment this is being written).

## Questions

Questions can be either frequently asked questions, or "next step" challenges we're looking to solve.

What is an ideal distance for Purple Air monitors? 6 months ago 1
What are some good trouble shooting tips for installing/maintaining a PurpleAir? 11 months ago 4
Is there an easy way (app?) to find my elevation above sea level? about 1 year ago 3
are real-time PM 2.5 push warnings from the PurpleAir possible? over 1 year ago 6
How do we get relevant PM data to residents in under 10 minutes? about 2 years ago 6
Using PurpleAir Sensor to monitor neighbour's second hand smoke about 2 years ago 2
Can you blur the location of a Purple Air device? almost 3 years ago 4
Vape detector about 3 years ago 5
What are the advantages to using 2 particle sensors at the same time? almost 4 years ago 11
How to interpret PMS5003 sensor values? almost 4 years ago 10
Is there a predictive relationship between the number of PM 2.5 and smaller airborne particulates compared to the mass of the same ug per cubic meter? almost 4 years ago 5
Questions about Plantower sensors from the University of Wisconsin - Eau Claire almost 4 years ago 5
Seeking sources of local wind/weather data almost 4 years ago 3
How do I calculate error for averages? almost 4 years ago 2
Should the Purple Air be co-located with a weather station? about 4 years ago 2
Why are the PM10 particles of the Purpleair monitor biased so high? about 4 years ago 7
What type of aerosol was used for the calibration of the purpleair lasers? about 4 years ago 5
Does particle composition that the purple air monitors measure greatly skew the data output? about 4 years ago 4
How can we connect a PMS5003 dust sensor to an Arduino? over 4 years ago 10
Sanity check for air sensors over 4 years ago 13
Pharmaceutical class 100000 particulate as compared to pm2.5 over 4 years ago 2
Low-cost air quality sensors to measure PM2.5, PM10? over 4 years ago 7
What challenges are people having with the PurpleAir? over 4 years ago 1
What is the correct AQI measure ? almost 4 years ago 18

## Activities

Activities show how to use this project, step by step.

Activities should include a materials list, costs and a step-by-step guide to construction with photos. Learn what makes a good activity here.

The PurpleAir sensor has two 'channels' that measure data. Channel A and Channel B. Each channel has a 'primary' and 'secondary' data set. The data that Channel A measures is described below:

PrimaryData

• field1: PM1.0 (CF=ATM) ug/m3
• field2: PM2.5 (CF=ATM) ug/m3
• field3: PM10.0 (CF=ATM) ug/m3
• field4: Uptime (Minutes)
• field5: RSSI (WiFi Signal Strength)
• field6: Temperature (F)
• field7: Humidity (%)
• field8: PM2.5 (CF=1) ug/m3 This is the field to use for PM2.5

SecondaryData

• field1: 0.3um particles/deciliter
• field2: 0.5um particles/deciliter
• field3: 1.0um particles/deciliter
• field4: 2.5um particles/deciliter
• field5: 5.0um particles/deciliter
• field6: 10.0um particles/deciliter
• field7: PM1.0 (CF=1) ug/m3 This is the field to use for PM1.0
• field8: PM10 (CF=1) ug/m3 This is the field to use for PM10

particles/deciliter is a particle count per volume measurement. ug/m3 is the particle mass concentration - the popular method of measuring particulate matter.

Channel B measures the exact same primary and secondary data. This is likely just done for robustness just in case one of the channel fails or has an error.

These setup instructions are included with the Simple Air sensors and can be reprinted Purple_Air_Instructions.pdf