Improving Indoor Air Quality
My home appears to have air quality issues and I’m seeking advice on possible solutions to the problem. I got an Awair element about a month ago and noticed that pm2.5 spikes pretty dramatically overnight. I’m most curious about permanent solutions this problem. Research has led to me to think that something like an ERV could help by constantly cycling outdoor and indoor air.
– the home was built around 1905
– previously a duplex, converted to a SFH
– it was redone in the early 2010s
– is a single floor
– has thick exterior stone solid wall construction
– a low slope roof and high-ceilings
– a low basement housing an 80% efficiency furnace; installed during the remodel. This basement is partially dirt with radon mitigation tarping; partially poured concrete for retaining walls and the floor.
I’m curious about what my best options might be and also what the cause of these indoor air pollution spikes could be. I’ve had the ductwork checked (it all looks fine); I vacuum every few days and have solid wood floors; and I regularly air the house out.
I’m tempted to think that my house is relatively porous and that outdoor air pollution is making its way into the house and stagnating; or possibly just pooling in the house.
We’ve performed a blower test and scored 6.37 ACH50. I’m in climate zone 5b (Denver).
Apologies if this is a bit of a brain dump, I’m happy to give more detail if it could help.
Thanks!
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Replies
Some studies show that PM2.5 peaks during nighttime hours: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4626967/ That study suggests atmospheric conditions.
As nighttime temperatures tend to be lower, various things may coalesce (e.g., aided by moisture).
Here's another article, from Nature: https://www.nature.com/articles/s41598-020-70179-8 That study also found elevated PM2.5 at night: "A peculiar enhancement in PM2.5 levels in the early morning and in the night time, even during lockdown, has also been examined."
"This implies that local meteorology and boundary layer dynamics control the diurnal variation of PM2.5. It is worth noticing that during the early morning and late night, wind speed is very low (< 1 m s−1) and temperature remains around 20 °C or less, which are favorable conditions for non-dispersion of pollutants. These low temperature and stagnation of wind movement in the absence of solar radiation also contribute to the formation of haze (unactivated particles consisting both of liquid water and other compounds by hygroscopic growth) and possibly mist (activated larger particles mainly consisting of liquid water)."
Perhaps you can set the device outside and see what happens. If it's an outdoor air issue, then tightening up your house may make a difference, with a 6+ ACH50, you should have some opportunities to reduce outdoor air coming in at night.
There are people who would advise you to tighten up your house with some strategic air-sealing before investing in an ERV in order to optimize its capacity to improve your air quality. Given the age of your home, I was reminded of this article, which you might find useful or at least thought-provoking: Adding Mechanical Ventilation to Old Houses.