Recently, a client asked to meet in a Costa Coffee. I accepted. It wasn't until the morning of the meeting that I realized it was a bad idea. Outdoor PM2.5 was 105 ug/m3 (3 times above maximum allowable health limits), which meant that inside would also be 105 ug/m3.
Over the past 10 years we've tested hundreds of spaces for PM (Particulate Matter), TVOC (Chemical Off-gassing), CO2 (Carbon Dioxide), CO (Carbon Monoxide) and several other parameters. Recently, the starlet of all these has become PM2.5, with special apps being created in order to tell us when windows should be open or closed, depending on how bad the outdoor air is. The reality is that it doesn't really make a difference.
Over the years, we've found that indoor PM levels are almost always 75-100% of outdoor PM levels. This is especially true of buildings that have fresh air systems, like offices, hotels and shopping malls. They typically have filters so coarse that all they keep out are the bugs. PM2.5 gets pulled in as though there were no filters at all. I've explained this thousands of times in lectures, trainings, meetings and conversations to people who thought they were safe indoors.
Yet, that morning I didn't need to explain anything. The coffee shop had both of it's doors wide open, welcoming the pollution in. Either the shop attendants were clueless or they knew that the fresh air system of the shopping mall was useless. Either way, the indoor air was miserable.
What added insult to injury was the amount of wasted energy and heat bleeding out through the open doors. A large proportion of PM2.5 comes from coal-fired power plants that supply energy to shops that waste it. This makes much of the pollution we breathe completely gratuitous. What would it take to install monitors and simple dashboards to track air quality and wasted energy, prompting staff to react? Virtually nothing.