If it’s not N95 it won’t be blocking out P2.5 particulates emitted from exhausts.

I wear KN95 masks, but I’m not breaking down the level of particulate matter that gets filtered for science. I’m saying I don’t get asthma attacks or sprayed by debris when I keep pace in traffic with a mask on.

Any mask will filter PM2.5 to some level. N95 is just more effective than some (but less than others)

And if it is, you'll have a much harder time breathing.

I have been wearing N95 when biking in the city for a year now. It is great, it is not difficult to breath at all (I am really incredulous at people making that claim), and it provides a measurable difference in the air I breath (a nasty but efficient way to measure that is looking at your snot if you bike while having a cold).

Thank you, I was repeating something I've heard, I do recall trying such a mask before covid in summer and finding it a bit uncomfortable, but maybe it varies.

I'm quite interested in better breathing when riding my bike when air quality ocassionaly drops so I'll give it a try!

In the particularly hot months I have had to use small piece of cloth under the mask so I can remove it after my commute and not have a humid mask on my face, but that was the only issue I had. Even with the extra cloth I did not have trouble breathing (I specifically try to not exert too much effort when commuting on a bike because the sweat on my back would be a much worse source of discomfort than the mask)

The masks they recommend in China are the N95 ones with valves that are banned in the west. My guess why is because they have to contend with both a pandemic and high pollution levels.

not sure if they're banned or not, they're not recommended because the valve lets you exhale unfiltered air, which is rather pointless for covid protection. For particulate filtering they're perfect though.

Recent studies show that valved respirators are actually better than or equivalent to surgical and cloth masks for source control:

https://www.cdc.gov/niosh/docs/2021-107/default.html

However, the "valves bad" mantra has been repeated so long and so strongly that it is unlikely there will be any official guideline change.

They are banned on planes and such. You can’t even really layer them since the second mask under would break the seal.

The theories on mask wearing are different there and here, or perhaps there is just more flexibility. Since China has such a low infection rate, the difference between an in-coming or out-going filter probably isn’t going to matter much.

OP here - I was on the Stanford campus in 2016 and 2017, frequently riding my bike there. Never once saw a mask on a bike rider. Very little car traffic on the routes bicyclists regularly use to get around. Also a frequent bike rider in my new city of Dallas. Very rarely (if ever), have I seen a cyclist (even on roads) wear a mask. Very likely masks on the Stanford campus are in response to COVID.

It’s understandable that you wouldn’t see people wear masks on campus prior to COVID. Mainly because mask wearing outdoors was previously a rare event for any reason in the USA prior to COVID, so you’d stick out as making a statement if you were one of the few who did. But the normalization of wearing a mask outdoors now likely plays a contributing role towards people feeling comfortable about wearing masks for other reasons that aren’t as straightforward as ‘preventing COVID’.

I also did not wear a mask when biking before COVID. Now, having easy access to masks, I would rarely bike without one, if I am near traffic, because of the better air it provides. Fair point about lack of traffic on campus though.

Indeed, before 2019 I would see masks most commonly on bicyclists. UK city roads are polluted.

They wouldn't have been wearing the 2 ply medical masks though if I recall correctly

Experience and a basic level of observation would show that you're reaching to find a justification here. It's clear that the masks are covid-related and not pollution related. Gymnastics are for gymnasts not for research.

Why would you ever assume that!? I also wear a mask when riding near traffic. Masks on bikers without helmets were a common sight in Paris in 2009 when I lived there. The mask has a measureable increase in immediate comfort, while the helmet is something that requires thinking ahead. Of course more people will remember a mask before they remember a helmet.

Is helmet wearing on bikes common in Europe anywhere outside of the UK?

German stats are afaik something like 20% (heavily skewed towards kids)

Not for casual riding.