Category: Environment

Post #1822: How much mulching could you do, for the fuel currently used for fall vacuum leaf pickup?

 

Suppose my town cancelled fall vacuum leaf pickup and disposal. 

Would the fuel saved by that offset additional fuel burned to run mulching lawn mowers, to take care of those leaves, in-place?

Best guess:  Yes.  Every lawn in Town could get an estimated five additional mowings per year, for the fuel currently used to vacuum and dispose of residents’ leaves. Continue reading Post #1822: How much mulching could you do, for the fuel currently used for fall vacuum leaf pickup?

Post #1821: Fairfax County staff recommend discontinuing fall leaf vacuuming.

 

True rumor

Source:  clipart-library.com  To me, the original for this seem as if it were genuinely old.  But I got it, presumably without copyright restrictions, from that source.  If this is new, kudos to the creator for the look of it.

Fairfax County Department of Public Works and Environmental Services (DPWES) employees recommended discontinuing fall vacuum leaf pickup. Continue reading Post #1821: Fairfax County staff recommend discontinuing fall leaf vacuuming.

Post #1819: Fire and rain

 

Today in Vienna VA we have rain.  And forest-fire smog.

This seems unfair, somehow.

This post asks two things.

Does rain clear the air?  That is, remove dust, pollen, and fine particulates?  And if it does, then why is my AQI in the 80s for fine particulates, after it’s been raining overnight.

On the flip side, does forest fire smoke generate rain?  That is, does the smoke in the air increase the chance of rain, as cloud seeding does?

Bottom line:  Rain clears the air.  But only a bit.  A typical value for PM 2.5 reduction by moderate rain might be 25%.  Forest fire smoke doesn’t appear to make it rain.  But if the atmosphere is already primed for rain, there is some evidence that a high load of smoke in the air will intensify thunderstorms.

Continue reading Post #1819: Fire and rain

Post #1803: Why are fine particulates (PM 2.5) so variable? It’s over my head.

 

One thing I’ve noticed about the AQI for particulates is how variable it is.  On any given day, my local hourly estimate from Accuweather will differ significantly from the EPA’s Airnow map.  Which, in turn, differs from readings just a few miles away.  For example, above, my AQI for particulates (as of 1 PM 7/6/2023 is either 63 (Airnow) or 33 (Accuweather).  Or somewhere between.

And readings within a few miles go as low as 13.  At the same time, the seemingly accurate meter I just bought shows “9”, sitting on my back screen porch.

At first, I chalked that up to instrumentation.  Maybe particulates are hard to measure, and what I’m looking at is more-or-less instrumentation error.

Because, serious, how could the air be so different, just a few miles away?  If I were to take some other measure of the atmosphere — temperature, humidity, pressure — it would vary smoothly over vast areas.   E.g., if it’s 90 degrees here in Vienna, VA, there isn’t going to be a pocket of 45 degree air five miles away in the City of Fairfax.  Yet you see that sort of apparent PM 2.5 disparity all the time.

So I thought, it must be poor instrumentation.  Then I bought a cheap air quality meter, noted above.  Not only are the readings stable from hour to hour, they are frequently in good agreement with the Accuweather numbers.  They clearly respond to ambient conditions in a hurry.  (The 4th of July fireworks briefly sent the meter into the “purple” AQI range, consistent with predictions from the Airnow map.)  The stated accuracy of the PM 2.5 measurement is +/- 10%.  All that, from a device that measures all five of the key air pollutants and costs under $75.

So, this isn’t due to instrumentation error.  Or shouldn’t be.  You can get reasonably reliable PM 2.5 measurements with a cheap off-the-shelf device.

Maybe my local variation is due to the presence of large local point-sources of PM 2.5.  But, to a large degree, we have no large point sources of particulate emissions in this area.  Largely because we are almost devoid of industry, in the DC area, and our power plants are (mostly) located outside of the metro area.

Which also matches my observation, because it’s not as if one area is consistently dirty.  It’s that the readings consistently vary a lot from place-to-place in this region.

So why do the PM2.5 readings in my area appear to be so highly localized?  Is there really that little mixing of the air between PM2.5 emitters, and local air?

Trying to understand how air mixes — a fool’s errand.

After about an hour of looking, I’m going to say that short of getting a graduate degree in atmospheric science, this ain’t gonna happen. 

It’s surprisingly complicated, but the joker in the deck is “turbulent mixing”?  Once I found out about that, I realized it was time to call it quits on trying to understand this.

First, physicists distinguish “bulk flow” (e.g., a breeze) from “diffusion processes” (molecules or particles moving through still air).  In this case, the latter would be the movement of water molecules or fine particulates through still air.

So, smoke spreads out because it 1) blows smoothly downwind, and because 2) the particles diffuse outward into surrounding clean air.

That said, it also spreads due to 3) turbulent mixing.  Any time the flow of air is not smooth (laminar, or layered), turbulent mixing is said to occur.  This sort of mixing can apparently distribute that smoke fully and more-or-less uniformly in the adjacent clean air.

Turbulent mixing occurs a lot in the atmosphere.  I’m pretty sure that it occurs at the level at which clouds form above the ground.  It occurs within clouds.  I occurs if sufficiently strong wind sweeps past fixed objects, e.g., tree branches.  And so on.  Anything sufficient energetic will kick the flow of the atmosphere from laminar flow to turbulent flow and turbulent mixing.

The bottom line is that there is no back-of-the-envelope way to determine how well PM 2.5 (including smoke) typically mixes into the surrounding atmosphere.  In the end, it’s all empirical, and depends on how hard the wind is blowing horizontally, how turbulent the atmosphere is in vertical profile, and so on.

Presumably, both water vapor and PM 2.5 move at the same speed, and mix at the same rate, when it comes to bulk transport and to turbulent mixing.  In both those cases, they are merely being carried along by the surrounding air.

But PM 2.5 diffuses a lot less rapidly than (say) water vapor.  A theoretical rule (via Einstein and Stokes) is that rate of diffusion is inversely proportional to the radius of the particle trying to diffuse.  Getting hold of some data (but not showing the calculation), that suggest that PM 2.5 diffuses about a thousand times more slowly than water vapor.

Diameter of a water molecule seems to be given as 2.75 Angstrom, where an Angstrom is 1/(10^10) meters.  Ah, round down to 2.5.  But PM 2.5 is in microns, or 1/(10^6) meters.  This means PM2.5 particle is about 10^4 = 1000 times larger than a water molecule.  Thus under this  simple theory, water (humidity) diffuses through still air roughly a thousand times faster than a PM 2.5 particle would.

At the end of the day, I have no clue whether that matters or not, with regard to widely varying PM 2.5 readings across my area. 

All I know is that even without big local point-sources of PM 2.5, it’s common to see big difference in (what appears to be) actual PM 2.5, across different locations in my area.  Whereas for other parameters of the atmosphere — temperature, pressure, humidity — true local variation in those quantities is tiny.

Seems kind of crazy to worry about it, but there has to be some good reason why this aspect of the atmosphere is so qualitatively different from others.

Maybe Hawaii wasn’t just a nice place to hang out.

Maybe my only clue comes from the Keeling curve (above) and how that is measured.  When Keeling started measuring atmospheric C02 in the late 1950s, he established his laboratory on the windward side of Mauna Loa.

And found average atmospheric C02 around 315 PPM.  Currently, it’s around 422 PPM.

But the point is why he chose that locale.  His goal was to get “well mixed” atmospheric gasses, and, apparently, having circa 6000 (?) miles of open ocean to windward was just the ticket for getting that.

By contrast, you can frequently find city air with C02 levels in the 1000-PPM range, near congested roads (reference).  That air hadn’t had a chance to get mixed with the rest of the atmosphere.

So, maybe Keeling located there for some reason other than it’s being a nice place.  Maybe you really need that much distance to ensure uniform mixing.  And maybe the mere 500 miles or so between me and the nearest Canadian mega-fire isn’t enough to ensure uniform mixing of the air.

So I’m guessing that the atmosphere doesn’t mix all that uniformly.  For whatever reason.  And that the small-area variation in PM 2.5 is true.  And that I should not expect it to get any smaller as the summer progresses.

Post G23-033: First backyard coyote sighting.

 

As a gardener, I try to keep an eye on the thievin’ varmints wonderful creatures of nature passing through my back yard.

As a retiree, I have nothing better to do.

But my eyesight ain’t what it used to be.

Keep that in mind when I say that I’m fairly sure I saw my first backyard coyote yesterday.

The pictures you might typically see — making the coyote look like some noble offshoot of the wolf — don’t match reality of the eastern Coyote.   Around here, if you see something about the size of an adult fox, but without the good looks, chance are, that’s a coyote.  If you see an ugly brown dog with a mottled coat and a long tail, not acting like a domesticated dog, chances are good that you’ve spotted an eastern coyote.

Background

This was not unexpected.  Coyotes are native to the western U.S., and have been expanding eastward for the better part of a century.  The predominant theory is that we invited them in by killing off bigger predators (wolf, bear), and converting forest into open areas.

I got my first-hand introduction to the Eastern coyote about five years ago, camping at Sky Meadows State Park.  That sits adjacent to the ridge of the Blue Ridge.

Just at dusk, the coyotes had themselves a howl.  At first, you hear a few individuals starting it off.  You think, oh, cute, that must be a coyote.  A minute later the entire ridge is ringing with the sound of howling coyotes.  Three minutes later they wind it down, and silence returns.

It was chilling.  There aren’t a few coyotes in those woods.  Like bear, or foxes.   There were hundreds within earshot of where I was camping.  At least by the sound of them.

In short, the Blue Ridge Mountains are infested with coyotes.  Given how few bear and foxes there are left, I’m guessing coyotes are now the dominant predator species in this area.  That’s a complete change from my youth, where there were no coyotes in this area, period.

And they are here in the ‘burbs.  There have been sporadic reports of pets being eaten by coyotes, here in the  D.C. area.  I think I spotted one crossing a construction site a few years back.

But it’s a different thing entirely to find one eyeballing your back yard. It skedaddled as soon as I opened my back porch door.

I would like to think I’m not the sort of person to form an opinion about animals based on cuteness.  For example, I loathe deer, for the destruction they bring.  Despite being handsome creatures.  Foxes, I like for the fact that they eat squirrels, and not just because they are really elegant-looking beautiful animals.

Eastern coyote?  My gut reaction is, one step up from rat.  They may be noble wolf-like creatures in the western climate.  And most photos you’ll see of them make them look the part.  But around here, they look like mangy stray dogs.  As in this view, from Wikipedia:

Good or bad?

Looks aside, near as I can tell, this newest invasive species brings along only one good attribute:  They kill deer. 

Better yet, they kill baby deer. More specifically, in many areas, coyotes are the number one cause of death for fawns.  (See, e.g., this random reference).

Much of the literature on this topic comes from the deer-hunting community, which of course tut-tuts over these premature deer losses.  The deer hunters have a valid point of view.  For them, coyotes are competition.  Having eliminated wolves and nearly eliminated bear in this area, the deer hunter is the only native carnivore that’s in competition with the coyote.

By contrast, as a back-yard gardener, I’m am definitely on Team Coyote on this one. 

However.

However, coyotes are omnivores.  Sure they eat fawns.  They also eat poodles.  And squirrels.  And garbage.  And fruits and berries, if there’s nothing else around.

Oh, and they are known to attack small children occasionally.  Just thought you might want to know, in case you were still harboring some sympathy for coyotes.

This invasive species is definitely going to put some pressure on our local fox population.  And that’s a pity, because the foxes in my neighborhood don’t go around hunting down my neighbor’s cats.  Or kids.

So if the coyote succeeds in pushing out foxes, we’ll have replaced a relatively benign and good-looking wild creature with one that’s far more of a nuisance.  And ugly to boot.  But one that is capable of reducing the deer population.

Summary

If Fluffy goes missing out of your backyard any time soon, you’ll know whom to suspect.

Coyotes aren’t advertising their presence.  They aren’t howling, here, yet.  (I think that’s a large-group activity for them and they aren’t yet that numerous.)  They are stealthy, and they are hard to spot.  They are easy to mistake for a fox or a stray dog.

But they are here.  As in, prowling the suburban back-yards of Vienna VA.

In the grand scheme of ongoing slow-mo environmental apocalypse — (reference insect loss, reference global warming) — I guess this hardly even registers.  Just another nuisance invasive species to deal with.

 

Post #1803: What’s normal for PM 2.5 in my area?

 

Currently our AQI is a mere 87, for fine particulates (PM 2.5).  That’s a relief.  Just a normal amount of air pollution.

Or is it?  I’ve kind of lost track of what was normal for my area.  It’s not like I paid attention to the AQI for most of the past decade.

So here, for Fairfax County, VA, I’m posting a table of AQI statistics, for PM 2.5. based on the period 2010-2022.  Just so that I can refer to it as needed.  Briefly, only 1% of days exceed the 99th percentile.  Half of days exceed the 50th percentile.  And so on. Continue reading Post #1803: What’s normal for PM 2.5 in my area?

Post #1802: How good is my car’s interior (cabin) air filter?

 

There’s little in the way of hard data available for car air filters themselves.

That said, the clear consensus of informed opinion is that in newer vehicles, setting the AC to recirculate will remove most of the fine particulates (PM 2.5) from the cabin air in a matter of minutes. Continue reading Post #1802: How good is my car’s interior (cabin) air filter?