Anything that I have tested empirically, or explain with detailed calculations, or just generally bother to get all the facts straight.
Source: Wikipedia.
There is no one-size-fits all Artificial Intelligence. Some write essays. Some paint pictures. No doubt somebody offers an AI that’ll pick your Lotto numbers. Continue reading Post #1811: AI options for blog posting
In 2020, we had an extended period when tomatoes would not ripen. That was new to me, but apparently that’s pretty common in the South. The lack of ripening is due to excess heat. But it’s not a daytime excess. It’s due to warm nights, as many varieties of tomatoes will not begin the ripening process (enter the “breakers” stage) if nighttime temperatures consistently exceed 70 or maybe 72 F. See Post #G22-43 for full details.
Source: Calculated from historical weather data from NOAA, for Dulles International Airport.
As explained in that prior post, the non-ripening is a subtle thing. Tomatoes that have already begun the ripening process will continue to ripen. But those that have not yet started that will remain green. So, at some ill-defined lag after the nights warm up, the supply of ripe tomatoes gradually dries up.
That “warm nights” thing is a pity, because climate models have long predicted that global warming will raise nighttime temperatures more than daytime temperatures. So it would seem that warmer nights are in the pipeline.
If you look at the graph above, that 2020 stretch of warm nights began in the middle of July.
Here’s the extended forecast for Vienna VA today:
It’s worth pointing out two things.
First, we’re surely in for at least a few nights above 70F. And, depending on whom you believe (and your misplaced trust in 10-day forecasts), we might be in for an extended period with nighttime temperatures over 70F.
Second, it won’t take one whole lot of warming to push all those forecasts above the 70F threshold. That’s going to make it tough to grow a whole lot of varieties of tomatoes around here, I think. But we’re likely talking the better part of a century from now. I hope.
Not me. I’m going to try a radiative cooling experiment. I’m going to see if I can use radiant barrier to reduce the nighttime temperature in parts of my garden.
It’s an unusual idea, but it’s not rocket science.
As I noted in earlier posts on this topic (G21-014 , G21-015 , G22-005 , etc.) a garden bed is like a big window, looking straight up into outer space. As such, it continuously radiates heat energy (long-wave infrared) upward, toward the cold of outer space. By my calculation, on a cold spring night, you lose more heat from radiation than from conduction.
That’s why a radiant barrier is what you want, for frost protection, for your garden beds. That can be a space blanket or similar material. But that’s also why a glass cloche works to prevent freezing overnight. And why a simple, thin-walled glass mason jar provides excellent frost protection for tender plants (Post G22-006). And, by contrast, why polyethylene sheeting does diddly-squat to prevent overnight freezing (G22-005).
But, weirdly enough, you can also use a radiant barrier for cooling, by preventing ambient radiation from reaching your garden bed at night. In effect, you make it so that your garden bed “sees” only the cold of outer space, directly over head. If the air is sufficiently transparent to long-wave infrared, your garden bed then cheerfully radiates energy off into outer space, and cools as a consequence.
This technique works OK in the dry desert, with a clear sky, which may explain in part why various Middle Eastern cultures have used it for millennia, to make small amounts of ice, in the desert (reference). That said, even under those optimal conditions, temperatures had to be near-freezing to start with. This reference suggest an upper limit of 5 C, or about 41 F. Ideally, a combination of insulation, evaporative heat transfer, and radiative losses would generate small amounts of ice, under those conditions.
By contrast, the main problem with using that here is water. Water vapor is the most important greenhouse gas. It’s plentiful in the atmosphere, and it absorbs and re-emits infrared across many parts of the infrared spectrum. Between the humidity and the clouds, a lot of what gets radiated into space will be, in effect, reflected (re-emitted) right back down to earth.
Which is, in a nutshell, the greenhouse effect.
OTOH, I only need a few degrees. If this can pull a 9F differential in the dry desert, maybe it can drop the temperature 3F on a cloudless Virginia summer night. After all, I’m just trying to trick those tomatoes into starting the ripening process. My understanding is, once that gets going, they will continue to ripen.
So it’s worth a shot, just out of intellectual curiosity. I’m going to set up a small enclosure made of radiant barrier — basically, a big tube with the open ends facing ground and sky. Cap that with a piece of clear polyethylene sheet to provide an IR-transparent barrier to the outside air. Then use temperature loggers to track nighttime temperatures inside and outside the enclosure. I might get lucky.
The nice thing about this method is that there’s zero energy consumption.
Probably ought to consider a shade cloth, as well, but I can’t quite figure out how that would be much help in terms of nighttime temperatures. Plausibly, the cooler the soil stays during the day, the cooler the area may be at night.
But if I’m willing to expend a bit of energy, I think a mist-cooling device would plausible achieve a sufficient drop in temperature. Mist coolers work by converting sensible heat (temperature) into latent heat (water vapor, instead of liquid water). I went over that in my post on the true energy cost of humidifiers, Post #1669.
That said, bathing my plants in mist all night just seems like a recipe for every tomato leaf disease known to mankind. So that’ll only be used as a last resort.
Otherwise, short of sticking a window AC under a tarp, and using that, I guess I’m at the mercy of Mother Nature here. If it’s too hot to ripen tomatoes, then it’s too hot to ripen tomatoes. Grow something else for the time being.
My garden beds emit “black body” radiation. That is, they toss out radiation at every frequency, with a peak in the long infrared. As a consequence, some of that is bound to be absorbed and re-emitted by atmospheric gasses.
But suppose, through some miracle of modern science, you could create a material that radiates infrared only on those bands of frequencies where the atmosphere is transparent to infrared. That is, frequencies that aren’t absorbed and re-emitted by common atmospheric greenhouse gasses.
Then — and frankly, this is where I lose it — you could, in theory, create a material that would literally cool itself below ambient temperature. If the air outside is 80F, your miracle-o’-modern-science could be 78F, with no power input. Just from enhanced “emissivity” in the right part of the spectrum.
Or, as these folks put it, emphasis mine:
... the PDRC coating demands a significant solar reflectance (Rsolar) in the spectral region (0.3–2.5 m) and a significant thermal emissivity (LWIR) in the environmental long-wave infrared (LWIR) propagation region (8– 13 m). As a result, during the day, the energy loss to frigid space ... is far more than the warming from daylight, resulting in electricity-free spontaneous refrigeration.
In other words, you could sit a piece of this stuff out in the sunshine, and it would remain cooler than the ambient air. With no energy input.
That’s close enough to magic for me.
AIs of various sorts seem to be able to do a lot of jobs that traditionally required the use of a human mind. They are particularly good with text generation. They can also easily do “literature reviews”, to offer a summary of current understanding or thinking regarding a topic. Some say they are good at writing computer code, but I’d like to see evidence of that before I’d believe it. Continue reading Post 1808: Some thoughts on AI, part 1.
Source: WTOP.
There was an article today on the local news-radio website (WTOP) regarding speeding in school zones. I took note, because I routinely drive through one of those zones where Fairfax County VA operates speed cameras. The zone is clearly marked, and you’d have to be blind to miss it, as shown above.
And yet:
In total, 23,431 cars were caught going 10 or more miles per hour above the speed limit in April, May and June combined.
I supposed I should be impressed by the sheer numbers. But instead, a completely different figure caught my eye: They only ticketed folks for going at least 10 MPH over the limit.
First, I thought it was intemperate of the reporter to note that exact figure. Anybody reading the article realizes that there’s no risk of a ticket at anything up to the posted speed plus 9 MPH. So, presumably, if generally known, that now becomes the de facto speed limit.
But second, I’d heard that same figure before, a few years back, in a discussion of red-light cameras and speeding cameras in Vienna, a town in Fairfax County. There it was phrased as “we don’t ticket unless they are going at least 11 MPH over the posted limit.” The explanation given at the time was that Fairfax County courts would not accept cases for any infraction less than that.
Short answer is, yes and no.
In theory, by Virginia statute, you can get ticketed for traveling one mile an hour over the speed limit in a residential area. This is my interpretation of § 46.2-878.2 of Virginia statute, which says :
Operation of any motor vehicle in excess of a maximum speed limit ... in a residence district of a county, city, or town ... shall be unlawful and constitute a traffic infraction punishable by a fine of $200, in addition to other penalties provided by law.
The black-letter law provides no slack. If you’re in a residential district, on a highway (meaning, in Virginia, any public alley, street, road, or highway), and you’re going a mile over the limit, you can, in theory, be ticketed and will owe a minimum of $200.
Except that the law spells out a different set of penalties for drivers caught by speed cameras in school zones. My interpretation is that because the process is, in effect, automated, they cut drivers a lot more slack than they would if they’d been pulled over, in person, by a uniformed officer.
In the case of speed cameras in a school zone (§ 46.2-882.1), emphasis mine:
1. The operator ... shall be liable for a monetary civil penalty ... if such vehicle is found ... to be traveling at speeds of at least 10 miles per hour above the posted ... speed limit ... . Such civil penalty shall not exceed $100 ... ... 4. Imposition of a penalty pursuant to this section ... shall not be made part of the operating record of the person upon whom such liability is imposed, nor shall it be used for insurance purposes in the provision of motor vehicle insurance coverage.
There appears to be no hard-and-fast rule regarding ticketing for how much “slack” you get, speeding in a residential area in Virginia. The plain language of State law in Virginia law says that if you exceed the posted limit, you can be ticketed. I believe that pre-empts any local law, as we are a Dillon Rule state. That is, local governments can only make their own rules where the Commonwealth grants them permission to do so. And nothing in Commonwealth statute appears to do that, with a few limited and explicit exceptions spelled out in the law.
Except that “ten miles over the limit” is written into law, in Virginia, for speed-zone cameras. There, the Commonwealth leans heavily in the direction of protecting drivers’ rights, and avoiding Big Brother information harvesting. So, in exchange for what is basically an automated process, you face a small fine. There’s a monetary penalty, but (as I read it) no points on the license.
First, if you are speeding, in Virginia, you lose any claim to having right-of-way. So if some bonehead does something to get you in a car accident, where you had the right of way, but you were speeding at the time … tough luck. You cannot claim right-of-way while you are speeding.
§ 46.2-823. Unlawful speed forfeits right-of-way. The driver of any vehicle traveling at an unlawful speed shall forfeit any right-of-way which he might otherwise have under this article.
The reason for that is pretty clear. Traveling at excess speed makes it difficult for other drivers to judge whether or not an accident will occur.
We had a horrific accident in this area, last year, that is a classic illustration of that. The culprit was a bozo who was driving a BMW about 80 MPH in a 35 MPH zone. His car got struck by a car turning left, and his car subsequently jumped the sidewalk and killed two high school student who were on the sidewalk, walking home from school.
Normally, the car going straight has the right of way. Should the car turning left have therefore been charged with the accident, for failure to yield right-of-way? I don’t think any sane person would suggest that. If nothing else, on a curved road, excessive speed of that magnitude more-or-less prevents drivers from seeing you coming in time. The accident was entirely the fault of the speeding driver.
Second, if you speed significantly in areas with red lights, you will run red lights.
Not may, will.
This point is courtesy of Road Guy Rob on YouTube. Yellow light duration is set based on expected traffic speed. (Plus regional variation, I guess). High-speed roads have long yellow lights, low speed roads have short yellow lights. In both cases, the length of the yellow allows drivers that are far from the intersection to stop before the light turns red.
If you drive at high speed, on a low speed road, there will be a stretch of pavement, and a rage of excess speeds, so that if you see the yellow light while you’re in that zone, you will literally be unable to avoid running the red. That’s because, between your reaction time and the car’s stopping distance, your car will travel much further than the engineers who set up the light expected. If you are within just the right range of excess speeds, if you see the light turn yellow, you both a) can’t make it through the intersection before the light turns red, and b) can’t stop before entering the intersection. No matter what you do — hit the brakes, hit the gas — you go through the red light.
And so, at some level, excessive speeding and running red lights go hand-in-hand. There’s a certain pleasing symmetry to that. My guess is, the folks who don’t care about the first, don’t much care about the second either.
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?
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 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.
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?
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?
This is not a post about obesity. Despite the fact that I have quit exercising on days where the AQI is high.
Instead, it’s about trying to weigh air pollutants. Continue reading Post #1801: Weight gain during air pollution alerts.
Along with much of the eastern U.S, we’re living through another round of air pollution alerts here in Northern Virginia. Best guess seems to be that those Canadian forest fires will be burning for months yet, so this will be occurring sporadically all summer.
I decided to see how the current situation looks, compared to historical air pollution levels in this area. To do that, I downloaded a little over two decades of daily data on fine particulates (PM 2.5) in Fairfax County.
I got some real surprises. Mainly, as high as the PM 2.5 levels have been, this June, that’s not a monthly record. In the 2000s (and presumably earlier) we routinely exceeded the monthly average level of PM 2.5 that we’ve seen in this smoky June 2023. Best guess, that was due to a toxic interaction of air-conditioning and coal-fired electrical generation.
It is exactly as I recall. Summertime air quality in the DC area was always bad. It had only recently gotten materially better. And then, along came these fires.
Details follow.
The EPA allows you to look up historical AQI data, at this website. For Fairfax County, and PM 2.5 (fine particulates), the earliest complete year of data is 2000. So that’s where this analysis starts. (Although the cutoffs for the AQI scale changed over this period, it appears that the website delivers AQI data uniformly using the current cutoffs.)
Source: Analysis of daily data from EPA website cited above.
The air got materially cleaner over this period. That’s clearly visible when I plot the annual average AQI for fine particulates (PM 2.5) from 2000 to June 2023. Back in 2000, the average was a bit over 50. By the time you get to 2015, the average was a bit over 30.
Best guess, around here, that was mostly a consequence of replacing coal with natural gas in our electricity generation mix. In 2000, half the power consumed in Virginia was coal-fired power. By 2020, that had fallen to just 4 percent. Almost certainly, the oldest and dirtiest plants were retired first. But this is also the era when regulation of particulates from diesels went into effect.
Source: Underlying data from the U.S. Energy Information Administration.
So far so good. But here’s where things turn weird. Let me now plot the same data as monthly averages, from January 2000 to June 2023.
Source: Analysis of daily data from EPA website cited above.
Surprise. Every year, in the 2000s, in the heat of summer, monthly-average particulate levels rose to the level they reached for June 2023.
I didn’t expect that.
I knew that we always had terrible ground-level ozone in the summer, but there are good reasons for that. Ground level ozone forms from the interaction of oxides of nitrogen and volatile organic compounds, acted on by sunlight and heat. We naturally got peak ozone during the peak of the summer season.
But what caused these August peaks in PM 2.5, that somehow was fully-phased-out by 2010 or so, I cannot quite fathom. Because July and August are the peak months for electricity use (in the U.S. and presumably in Virginia), I’m guessing this also has to do with electricity generation and the change in the generation mix of the Virginia grid.
And, by inference, about half the improvement in the yearly averages was due to getting rid of those July-August peaks. You can see that the annual minimums declined from about 40 to about 30, or half the decline in the annual averages.
My only real point is that, two decades ago, every summer, monthly average particulate levels in this area exceeded what they were in June 2023.
When I plot the worst day in each month, then June 2023 finally stands out against the historical background. In the 2000s, we routinely had Code Orange y AQI days for fine particulates (AQI > 100). But we never had a Code Red day, that is, AQI over 150. By the 2010s, Code Orange days had become rare.
In any case, since the start of recordkeeping in 2000, we hadn’t had anything close to the AQI of 198, for particulates, that we saw in June 2023.
So that’s how to characterize this situation around here. We have occasional days with incredibly awful air quality (for particulates), compared to historical averages. But the average for the month isn’t even as bad as it was back in the days of air-conditioners running on coal-fired electricity.
In a nutshell: There is no hard cutoff. More air filtration is better. But there are clearly diminishing returns to buying the ultra-high-end air filters.
The bottom line is that, when it comes to the current air quality alerts, some air filtration is a whole lot better than no air filtration.
