Well, all you’re saying is right. But it’s also pretty unlikely to really find a single Pb atom flying around. There’d be a gradient originating from the source, with most heavy Pb atoms actually chilling at the source and not wanting to really move (think elastic impact) as all the other atoms/molecules colliding with it have way less mass. Only the most energetic ones escape (we’re overlooking any kinds of wind here for simplicity, just focusing on the thermal energy). So Pb will most likely see other Pb and form more inert clusters before even noticing any other molecules flying around. Those clusters will get oxidised on the surface eventually, but definitely not instantly or „quickly“ (however uncertain that term might be).

Now, in a realistic scenario, with wind working it’s magic and mixing everything, you’re probably right to disagree. That’s why my answer was „yes and no“. Realistically, it’d probably get oxidised at some point. Even a radical reacting with another radical needs to (Pb and O2/O•) fulfil certain strict geometrical conditions in order to pair the lone electrons. Those conditions can only be achieved randomly and under a certain energy threshold, which is why radicals in gas phase can be (but definitely don’t have to) pretty stable. I aimed to explain the reasons why this isn’t really a straightforward case.

Again. So basically, it’s pretty unlikely that a single Pb gets quickly oxidised. It will happen to some atoms though. It’s way more likely for Pb to form bigger clusters, which are more probable to hit (or rather be hit by) oxygen to react on their surface.

Edit: I’m all for napkin math though. I’ll try to remember to do it later.

Yes and no. That totally depends. Chemical reactions are actually really unlikely to happen, as the right particle has to hit another appropriate particle under just the correct angle with the right energy (collision theory). Those prerequisites make chemical reactions pretty much a numbers game. It’s entirely possible for the lead atom to just bounce around for a really long time and work it’s way to the ground.

In the air, Pb most likely to react with oxygen, so like 20% of the entire air mixture. Now think about a single Pb atom as a grey ball (albeit a rather big and heavy one) in a big room with 10000 (most gases consist of surprisingly low amounts of molecules) other balls. Only 21%, so 2100, of them are reactive oxygen, which is evenly distributed and well mixed with other ones in the room. Now, the heavy big ball bounces around and hits mostly nitrogen, which doesn’t do anything. If it hits oxygen, it needs to fulfill all the above conditions to actually oxidise instead of just bouncing off of it.

Basically, looking at an individual atom, its pretty unlikely it’d react with anything. Looking at bulk atoms, as they practically never are singled out, reactions are way more likely to happen.