Mandating Mask-Wearing by Logical Fallacy?

This would be a Appeal to Common Sense Fallacy. 

Just because a thing is or isn't commons sense has no bearings on whether its true or not. 

Unfortunately in a democracy, making mandates on appeals to common belief is how decisions are made. 

The justification proffered as basis for this mandate by both the Mayor and commissioners: " It's just good, common sense."

I think you're confusing the basis for the decision and the manner in which they are appealing to people to follow the rule. 

In simplistic terms, people breath out vapour (imagine a cloud of vapour billowing our by 2 or 3 feet on a cold night, that's still there when you can't see it condensing due to the temperature change), and vapour can carry pathogens. Pathogens can land on a surface or directly onto someone and spread. A cloth covering can filter out and/or reduce the reach of the vapour. In that context it would seem like common sense to use face masks. 

There is science behind it, and there are science deniers and conspiracy theorists, and rights violation Karens. 

I think claiming something is just common sense is exactly the Appeal to Popularity , but it also has the spurious basis of Appeal to Authority , since it arises from a governmental mandate.

Neither is a bar to accuracy, and the tone of reaction here sounds more like ODD, based on Argument from Fallacy in which some deny the argument because it has a fallacious component.

A mask is a screen with physical limits of particle sizes, but anyone who uses a clothes dryer knows that the screen is much larger than the finest particles in the dust from their laundry load. No doubt some dust particles get through, but the argument that the mask is not perfect is a Nirvana Fallacy .

Any infection requires a dose of infectious particles. often called a minimal infectious dose (MID), and while the article in wikipedia https://en.wikipedia.org/wiki/Minimal_infective_dose focuses on bacteria, the concept applies to viral infections as well. 

This is not a novel idea, and, imo, if the mask reduces the probable dose one might receive from a nearby carrier, it makes "common sense" to wear it.

I find it interesting - perhaps indicative of this group's argumentative bent and a sort of sophistry - that on the one hand we read that everyone should wear a mask, now that Fauci has said so and despite the prior practice of Trump, and now in response to this question, we read several respondents' demanding scientific evidence and peer-reviewed support as a basis for opposing the "common sense".

I wear a mask, an N95 mask I've overlaid with nano-silver.  Nano-silver has at least 18 peer-reviewed references to killing viruses, including a prior SARs virus.  I decided common sense was preferable to waiting for a peer-review of Covid 19 as if it special qualities unlike any other bacterium or virus.

Don't knock "common sense" just because you can find a link to a fallacy.  If you don't understand how filters work, get someone to explain them to you.

I do agree that "It's just good common sense" is not a good argument, nor a conclusion to an argument. Wearing a cloth mask to protect the population against Coronavirus spread is nowhere near being in the "common sense" category like "looking both ways before crossing the road" is, and pretending it is appears to be an attempt at not having to justify the policy.

Related to the argument but unrelated to the fallacy, there is enough data at this point to show wearing cloth masks slow the spread of the virus. But even this fact wouldn't justify a make requirement. We would need a "should" in there somewhere. For example:

P1. We should take actions to slow the spread of the virus providing the actions don't take more away from our collective well-being than slowing the spread of the virus adds to it.

P2. Mandating wearing masks slows the spread of the virus and takes away very little from our collective well-being compared to what it adds to it.

C. Therefore, we should mandate wearing masks.

As I understand the Citizen's comment, he considers "common sense" to be "what many people believe to be true".  I've always considered "common sense" to mean suggest a process for reaching a sound and prudent judgement by using an average amount of skill and knowledge of the subject.  Given the potential for folks to understand at least two different things from the undefined (here) expression "common sense", aren't we also getting into Equivocation, too?