Hi wooper,
Thanks for the post! This is certainly a sizable discrepancy, and I’d generally recommend following our sensor maintenance guide to address this. I understand that you performed a cleaning with your bike pump, but were you able to target those four collinear holes in the unit as outlined in that guide? If there hasn’t been an improvement after doing so, you can take them apart as you’ve mentioned, and that step is mentioned under the “Optional Steps” section of our maintenance guide.
If you’d prefer not to perform a deeper cleaning, a replacement is a perfectly reasonable way forward as Tinashe has mentioned above. You can of course purchase them from a third party if you’d like, though the benefit of getting replacements from us is that we test them in our facility.
Additionally, if you’d like to let us know the device ID of your sensor at contact@purpleair.com or in a direct message to me, I can take a look at its readings and apply downgrades to erroneous channels if necessary.
Happy to help with any additional questions or need for clarification on this!