Coronavirus & Air Pollution

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John Wilton-Davies

Air pollution is usually split into two types – gaseous and particulate.  Each category consists of both naturally occurring substances and those produced by human activity and, whilst we often think of pollution as primarily man-made, naturally occurring particulates and gases can be the source of considerable health hazards. Think here of wildfires in particular, but also pollen, for those who are especially sensitive, ozone, formed naturally in sunlight, and, as is relevant today, viruses and bacteria.

This isn’t intended to be a forum to discuss coronavirus but, as it is clearly a form of air pollution, there has been much commentary and consideration of the use of various air pollution reduction measures to potentially limit the risks of becoming infected.

It’s believed the major vector for transmission of the virus is breathing in droplets from an infected person, most commonly from being ‘within range’ of a cough.  Infection through contact with infected surfaces comes a close second.  Skin contact in itself won’t cause problems but passing the virus to the airways (or tear ducts) by touching your face with your contaminated hand will do so.

If you don’t go near anyone else, and keep your hands clinically pristine, you won’t catch coronavirus.  But in the real world, what measures might give protection and how much?

Hand hygiene is vital.  Anything else you do will be wasted unless you ensure you don’t pass virus from surfaces (or other people –no handshakes!) to your mouth or eyes. And this is where a common question is applicable - how useful are...

Face Masks

Firstly, it has to be said, a face mask is not a face mask. There are hundreds of different types and, it has to be said, the way most are used they won’t prove particularly protection against catching a virus.  

From a physical viewpoint, the two crucial features of a face mask are the size of the mesh through which you are supposed to breath – fairly obviously, the smaller the holes in the mesh, the smaller the particles that will be trapped, and the fit.  Most masks are not designed to fit snugly around the face (think military gas masks) and, as a result, the easiest way for breath to come and go from your lungs is around the edge of the mask rather than through the mesh, as intended.

Still, the finer the mesh the better (for trapping particles), but finer mesh means more air resistance so more air passes around the sides in a Catch 22 scenario. Also, finer meshed masks, and certainly better fitting ones cost more.  And, if it costs more, people hang onto it longer, running the real risk of turning your virus –protection plan into a breeding ground on your face.

Despite this,cheap masks may serve some purpose.  With a fabric or paper screen covering your mouth and nose you’re much less likely to be touching your face with potentially contaminated hands and, even though someone else’s virus may get through to you, your chance of infecting others is reduced as even a larger mesh may capture a large proportion of the larger droplets from any cough you have.

But if you’re really worried about catching the virus in a public place your best bet is to avoid going out.  Anything short of a full-face gas mask, properly sealed around your face will only slightly reduce the risks.

Air Purifiers

We’re asked a lot if an air purifier can help and it’s a similar story to that for face masks.  Firstly, a good, HEPA quality filter WILL capture viruses and probably keep them locked up for long enough that they won’t pose an infection risk. After all, viruses are just another particle and a purifier doesn’t differentiate between natural and man-made pollutants.

BUT:

Only a HEPA quality filter will capture particles as small as a virus.

A purifier can only capture particles that are drawn through it.  Leave one running for a while in an empty room and it should clear the air quite effectively, but common sense must apply here.  If you’re in a room with an infected person they will likely be breathing virus in your direction before that air passes through the purifier.  It can reduce the risk of infection, but certainly not eliminate it.

Purifiers can really only be useful generally in an enclosed space where they can reduce the overall pollutant level in a fixed volume of air.

Our advice is that you should not rely on either face masks or purifiers to protect you but both can be potentially useful if used with a bit of thought.

Indoors, or in a car, the risk of infection from another person is much greater than outside, where air currents dilute any virus much more rapidly.  A good purifier and/or combined with sensible airflow can bring the risks down a little.

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