Yes of course is air quality inside is strongly related to outside air quality. Installing a filter system is definitely something we are planing for the future (when more high end miners are deployed). As for the moment we have to make it work without one. But even when we have a filter system I would like to be able to evaluate how good or bad it is working. Thats why I am monitoring air quality.

From my research data centers typically aim for particulate matter concentrations of less than 1µg/m³. I suppose similar thresholds should be applied for mining farms as well.
This information can be found at section 3.1 in Table 2 in the following document: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.362.2554&rep=rep1&type=pdf

Contradicting to this Oliver from the WhatsMiner Support on Telegram (https://t.me/whatsminercommunity) has told me that WhatsMiner devices should be deployed in environments with particulate matter concentrations of < 0.5mg/m³, which would mean < 5000µg/m³. Oliver may have mixed up the units here (meaning he wanted to say < 0.5µg/m³) but nonetheless I feel as if it should be easier to find accurate and valid information on this.