Another indoor air quality conundrum

Yesterday, the UK government announced that all remaining restrictions relating to Covid-19 are to be relaxed on July 19th. There will no longer be a requirement to work from home when possible (something that seems to have been gradually ignored by many organizations for weeks already) and schools can abandon bubbles and even mask wearing and social distancing.

To mitigate some of the effects of increasing infections and the removal of passive measures such as masks and distancing, better ventilation of buildings is encouraged.

One way to measure ventilation is by using a proxy measure of carbon dioxide concentration, and that is pretty easily achieved with IAQ monitors. Carbon dioxide concentration is a good proxy measurement for ventilation as the higher the levels of CO2, the fewer air changes are taking place. If CO2 levels are high, then increasing ventilation is a good option. Not only will it have an impact on virus transmission, but it will also improve cognitive ability and reduce the risk of drowsiness. High levels of CO2 are very much associated with poor productivity.

Awair Omni OAQ monitor

The easiest way to improve ventilation is to open some doors and windows. In most schools, that is the only way to do it – very few schools have complex HVAC systems that can adjust ventilation rates and still pass air through filters.

If you have an IAQ monitor that measures a range of parameters, such as particulates and VOCs as well as CO2, then as soon as you open a window, you might discover that other pollutants increase rapidly – and then what are you going to do? Balancing the health risks of the different contributors to poor IAQ is hard enough already, without the added complications of a nasty virus

Many schools, especially those in urban areas, as well as office buildings, are situated near busy roads and particulate pollution especially is known to be very damaging to respiratory health. Measurements of particulates near roads are sometimes way above safe limits and high concentrations of fine particulates can kill or seriously damage health.

Photo by thevibrantmachine on

So, here is the puzzle that has to be solved. Will opening windows to reduce the risk of ill health due to airborne viruses (such as Covid-19) cause a bigger impact on health by letting in a whole load of other pollutants, especially fine particulates?

There are, of course, some things that can be done to reduce the amount of particulates getting into buildings.

The first is to reduce them at source. In urban areas, the main source is traffic, especially traffic using internal combustion engines. The rapid increase in electric vehicles is certainly going to help, but it will take many years before they are off the roads completely, and the most polluting types of vehicle are the hardest, at the moment, to electrify (big goods vehicles).

Next, you can try and reduce the chances of those particulates getting inside a building with open windows. This is not going to be easy, but there are some effective measures, and they are mostly green.

Green walls, green screens, climbing and scrambling vegetation, trees and hedges are all capable of trapping large quantities of particulates on their foliage, and have an impact on urban heat islands too.

A Mobilane Ivy screen trapping particulates and keeping the noise down

Trees, hedges and plants like ivy are actually quite cheap too, and they are self repairing. They also reduce noise and look good too.

In the short term, using ventilation to flush out viruses (along with excess CO2) is going to be better than leaving windows closed and minimizing the ingress of fine particulates, but that is not a viable long term solution. Ideally, we should always have good ventilation to flush out viruses (it would be a good idea to use ventilation against all respiratory viruses, not just Covid-19), but if that is the case, we must do more to prevent other pollutants getting inside buildings. Vegetation is going to help a lot, but removing the source of those pollutants has to be the ultimate goal.

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