Your primary exposure to outdoor particles occurs within you house. How can that be?

Every house has an air exchange with the outdoors - it varies with house operation, outside temperatures, and the leakiness of the home. There are many ways for outside air to enter, carrying their particle load. And most importantly, folks spend the lion’s share of their lives inside their home. With 400+ participants using 3-4 monitors per location, we have learned a lot, and the trends are consistent across different air quality conditions and housing stock.

Many people open lots of windows in the summer for “fresh” air or night cooling. What do particle counts look like in such a house? Here’s one example from the ROCIS Averager. The Averager is described on the ROCIS website here: http://rocis.org/rocis-averager

Hard to tell the difference between the line for the “Inside” vs. the “Outside”, isn’t it?

But what if the windows are closed and there is good particle filtration happening inside the house? Do the outside concentrations affect indoor levels? Here is an example where the inside counts are far below outside but the pattern of outdoor particle rise and fall is obvious.

This household has very few indoor peaks caused by particle-generating activities inside the house (e.g. cooking, jumping on the couch, burning candles, etc.). This makes the effect of the outdoor air clearer. What we see in this graph is that outdoor particles are still entering the house but inside counts are roughly 90% lower than the levels seen outside. There is still an effect of outdoor particles but the particle exposure inside is far less than you would experience if you stood outside.

The ROCIS Data Explorer provides another means of visualizing this outdoor/indoor relationship in the Low Cost Monitoring Project homes. A description of the Explorer is available on the ROCIS website here: http://rocis.org/rocis-data-explorer The bottom graphs of every Explorer provide three comparisons for the data from each house:

1. The indoor particle counts when outdoor air is in the top quarter (or highest particle counts) of all observed concentrations.

2. Conversely, the indoor particle counts when the outdoor air is in the lowest quarter (i.e. best) of all observed concentrations

3. And, in the middle, what the indoor air is like when the outdoor air is close to the average conditions

Here is one example:

The bottom bars show the indoor and roamer particle counts when the outdoor air is best. There is lots of “green” (Dylos “Good” to “Excellent”) in the bar. The top bars indicate that there is very little “green” and much more “red” (Dylos “Poor” to “Very Poor”) in this house when the outdoor air is at its highest concentrations. We see this stepwise pattern in the data of almost every house.

If the outdoor air were better, all indoor spaces would benefit.

It is critically important to improve outdoor air quality. The American Lung Association's 2021 State of the Air Report ranks Pittsburgh's airshed the worst east of the Rockies for 24-hour and annual particles. What can households do to reduce their exposure?

On January 26 the National Academies of Sciences, Engineering, and Medicine (NASEM) has published the proceedings of the workshop Indoor Exposure to Fine Particulate Matter and Practical Mitigation Approaches.

To download a copy of Indoor Exposure to Fine Particulate Matter and Practical Mitigation Approaches: Proceedings of a Workshop, visit: https://www.nap.edu/catalog/26331/indoor-exposure-to-fine-particulate-matter-and-practical-mitigation-approaches

For more information about indoor particulate matter and related activities at the National Academies, visit: https://www.epa.gov/indoor-air-quality-iaq/indoor-particulate-matter

To view the video recordings of the indoor particulate matter workshops, please visit the following link and scroll to the bottom. The workshop dates are listed and videos can be found upon clicking each individual date and scrolling to the bottom of the page. https://www.nationalacademies.org/our-work/indoor-exposure-to-fine-particulate-matter-and-practical-mitigation-approaches---a-workshop