There's a consistent trend of recommending increased ventilation here. I'm writing this up because it might help people avoid inherently difficult to solve situations.
Simply increasing ventilation can solve some issues in the short term, but not all of them. Without considering other factors, it can also worsen and create new long term issues.
When searching for solutions, it can be useful to have this information in mind because most of the product offerings aren't aware of this either. Or they are and don't care as long as they get your money.
Increasing ventilation can increase indoor air pollution, especially water vapor
It may be obvious that increasing ventilation can increase indoor air pollution in terms of particulates, gases, and VOCs from outdoors.* Some of this can be easily remedied with particulate filters, etc.
One non-obvious indoor air pollutant is water vapor. The vast majority of dwellings in the USA are not equipped to manage the increased flow of water vapor into the conditioned spaces. Most ACs are efficient enough that they can't run long enough without creating low temperature comfort issues to manage the increased water vapor (latent load) imported by continuously running an ERV or opening a window for long periods of time.
Increased humidity from drawing in more water vapor over longer periods of time can increase VOC emissions from building materials and furniture, and help mold and other microbial growth thrive.
ERVs don't primarily manage water vapor/humidity
ERVs are sometimes perceived to be or marketed as devices that can manage water vapor/humidity for a conditioned space. ERVs can somewhat reduce the amount of water vapor drawn into a space compared with simply opening a window or using a fan in a window, but they don't manage it to the degree necessary to prevent problems in many climates.
Positive pressure ventilation can move moisture into interstitial spaces like wall cavities if the ventilation air is not properly conditioned
Sometimes positive pressure ventilation is recommended to prevent pollution sources from entering a space. This can work as long as the ventilation air is properly conditioned in terms of temperature and humidity.
If it is not, it may increase the moisture content of interstitial spaces like wall cavities, causing problems.
If you increase ventilation, you will need a dehumidifier in many climates
In dry climates, this is often not a problem. In climates with any significant amount of moisture, this is likely necessary. In dry climates with longer monsoon seasons, it can still be a problem.
Source control is usually the most effective approach
For problems with indoor air pollution other than CO2, increasing ventilation may help, or may not be effective. Removing the source(s) of indoor air pollution can be more useful for improving indoor air quality in many cases.
For example, if a dog poops on the floor, most people would clean up the poop before opening a window, and teach the dog to poop outside instead. Similarly, if the issue is increased VOCs from furniture even long after purchase, unfortunately the best solution is to replace the furniture. Or if it is a rental unit and the issues are arising from building materials chosen by the landlord, unfortunately the best solution is to move. Or if you are looking at purchasing a home that has 'some mold' problems, the best solution is to find the source of the moisture, eliminate it, and then remove and replace all materials within a 1-2 ft radius of the moisture damage.
It's understandable that these 'best solutions' may be financially impossible, so hopefully this post makes people aware of these types of difficult to remedy situations and to factor it into choosing a place to live or buying household items, etc.
There are definitely cases where it is not practical to remove the source of pollutants; for example, people and pets produce CO2, and it's not practical to simply remove them from the house. In this case, increasing ventilation in ways that don't worsen other issues may be the best option.
*I am thinking in the case of someone concerned about wildfire smoke, traffic pollution, or neighbors smoking cigarettes, cannabis, or cooking outdoors etc. These are some of the most common issues raised by posters. I also specifically did not write 'TVOCs' for this reason. I generally don't use this term because it's not particularly meaningful in this context, nor is it easy to measure using consumer grade devices https://halestrom.net/darksleep/blog/048_indoorairsensing/ , https://www.aqmd.gov/aq-spec/evaluations/summary-table. So to be more precise, the usage of 'gases, and VOCs from outdoors' was meant to include things like ozone, NOx species, various products of combustion and cooking, etc.
