Pm2.5 does not continually build up in the global environment, at the rate it is generated, else the entire globe would be a soupy smog. So, where does it go?
Of course local current pm2.5 can be blown elsewhere or diluted, but it’s a different question that I’m pursuing.
Does it break down into non-pm2.5 material? Does it clump up into larger material?
Even if rains or snow can wash limited amounts of it from the air, where does it go next? Does it retain its character when attached to a water drop, and then get ingested with water, only to reach our bloodstream via that route with similarly detrimental effects?
If I generate pm2.5 wood smoke in my wood stove, does that affect my neighbor a mile away (or 25 miles away), just at a diluted rate, or is it somehow neutralized over that distance into something else?
Can sunlight or ultraviolet break down pm2.5 over time?
If it causes acid rain, does that mean the pm2.5 particle no longer exists as such and is no longer detrimental as such?
PM2.5 particle pollution can travel a long way.
One example was forest fires in Portugal - particle pollution reached Scandinavia.
In winter when wind blows from southern Europe we get particle pollution in North. If you look at map you can see why…
Yes, pm2.5 does travel, and dilute. But if that were all it could do, and the total distributed amount around our globe kept building over the decades, without breaking down, then the global average levels would rise continuously.
They don’t seem to. We still see lots of zeros on the map.
So, what are the mechanisms of particulate breakdown? Is there a way to accelerate that process?
Granted, prevention at source is a better plan, but we also put a lot of effort into removal by filtration. Are there feasible also ways to assist or promote transforming the particulate into something less threatening?
Or, instead of accelerating a breakdown, could it be clotted into larger stable particles?
The atmospheric lifetime of PM2.5 varies depending on the chemical composition of the particle. Water soluble aerosols like sulfate and nitrate suck up water vapor and get big enough to rain out or settle. Black carbon and some organic carbon particles don’t pick up much water and can take a month or more to be removed, by aglomeration and eventually either dry deposition or rain-out. But all PM, of any size, eventually is removed – in a time frame of a month at most.
George, thanks for the explanation.
I’m left wondering if there’s a cost effective way to accelerate those rain out, settling or aglomeration processes, or perhaps sequester settled/deposed particulate so it doesn’t travel further.
Though, of course, it would be preferable to prevent generation of the particulate at its source.