I had a heck of a time finding it, but what I did was to got to the website where my sensor was, click on "get widget", and noted the number. In my case it was 6 digits, not 5 like has been stated before:
Then I requested and received my API read/write keys from Purpleair and used the read key.
Worked for me!!!!
Thank you! That worked
Never changes.
Hey everyone. Hope you are well. I am trying to get data from my PurpleAir sensors into Sharptools. My outdoor sensor works great, but the indoor doesn’t pick up data. In case it helps, I’m trying to pick up sensor 133282, which is located in Random Hills VA.
Thanks so much for any help you can offer 
Do you have your Private key, that is the only real difference between the public (Outdoor) and private (Indoor) sensors. The key should have been provided when you registered the device otherwise Purple Air support could probably provide it. The fork below works for both my indoor and outdoor sensors.
Edit:
I figured the payment thing out. You start with 1,000,000 points with a new account. They are credited to your organization, You then have to transfer them to a "Project". Once I added points to my project I started receiving data from a nearby Purple public sensor.
I created a new driver using the gethub code. Says the version is 1.1.10. I was able to go to purple and create a read and write api key. However they now require a payment. Looks to be a minimum of $10.
That explains it. Being the belt-and-suspender kinda guy I am, I prolly burned through my first 100,000 calls in, oh, about a day. 
Thanks so much
Cross posting: Would it be possible to draw up a driver that would instead of using the cloud, use the local network IP address to provide the data to hubitat?
Apparently MeteoBridge has done that and is pulling the data from the local IP.
The deeper reason are (1) emerging pay for service scheme at PurpleAir (2) sensors going broke (3) needing only local value (related to (1)).
I'm encountering the same problem as @Busthead. Current states reports as "timestamp: initializing" but nothing changes. Is this driver working for others? I am hoping to use this to pull data from local sensors listed on the PurpleAir map, and I don't have my own device? Is the functionality of this driver limited to users that have a PurpleAir private key for their device?
I don’t recall what I did to fix this but it’s working for me now. I’m using an API key.
Double check your settings and Save Device again.
Yup!
I have resolved this immediate issue, but I am left with more questoins.
I discovered that Hubitat Package Manager had installed @storageanarchy's driver version 1.1.08. I installed version 1.2.0 from mgroeninger, forked from SANdood, which conform with PurpleAir's current API setup.
I also created an API key for PurpleAir. For other's benefit the process is described here.
This definitely enables communication with PurpleAir, but I have yet to find any devices from the map that I can query successfully. Is it possible that I need to provide a "private key"? Has anyone else had success requesting data from public PrupleAir devices they do not own? If so, what Sation ID are you using (so I could test my setup)?
In the meantime, I have chosen to use the AirNow driver from csteele, installed from Hubitat Package Manager, which provides most of the information I'll need about regional air quality.
This works well (tested and running), and you do not get charged for downloading your own PurpleAir data on your home - or if the PurpleAir does not report to the cloud anymore - which can happen.
Download the Hubitat app
