I thoroughly enjoyed reading this in-depth article. As we're working on air quality at Airica, it's great to see that this topic is getting more attention lately. We focus on easy to deploy air quality monitoring for schools and offices. In these spaces it's just as much about CO2 as PM as high CO2 levels reduce cognitive performance significantly. This 2016 study shows 61-101% better cognitive scores in well ventilated buildings: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4892924/