Anything that I have tested empirically, or explain with detailed calculations, or just generally bother to get all the facts straight.
Right now, Europe is experiencing a record-breaking heat wave, thanks in large part to global warming. Ask me some time about arctic amplification and the destabilization of the jet stream. Continue reading Post G22-042: There are no ripe tomatoes in hell.
To cut to the chase: Copper versus citric acid. That’s what I’m going to test this year, for control of powdery mildew on cucurbits.
This post shows how I got to this end point, from my original plan of a formal test of several “home remedy” approaches to controlling powdery mildew.
Using citric acid to control powdery mildew was news to me. There are, however, at least two commercially-available mildew-control products that are little more than a dilute solution of citric acid. Roughly one-twentieth the strength of typical commercial lemonade. So that’s surely worth testing. Continue reading G22-039: Powdery mildew products, Amazon search, and a change of plan.
The American penchant for ignoring the rest of the world never ceases to amaze me. And so, after reading my N-hundreth story about U.S. inflation rate — with nary a whisper about the rest of the world — I felt motivated to blog about the elephant in this particular room.
Much of the reporting on U.S. inflation is fundamentally idiotic. It’s noise generated for political advantage, with no content. It’s all about exploiting an opportunity for finger-pointing. It lacks substance because all of that reporting assumes there’s some unique U.S. cause to our unique U.S. inflation.
I was going to invest maybe a whole ten minutes in looking up the current inflation rate in selected countries. But this is the age of the internet. Maybe somebody put all that information in one convenient place.
So that, if for some peculiar reason, you, as an American, actually wanted to know what the inflation rate was in countries other than the U.S.A., you wouldn’t even have to search for it. Just look it up on the Financial Times website.
This takes the drama out of doing this one country at a time, but it gets right down to the bottom line. Here are graphs of the inflation rate in the U.S., North America, Europe, Asia (other than China), and the world as a whole. (I exclude China because they don’t have a credible domestic inflation measure.) These are all taken from the Financial Times website.
Notice anything?
Now it’s time for Occam’s Razor. On the one hand, maybe each of these countries has some unique, specific factors boosting their individual rates of inflation. Simultaneously.
Or, just maybe, something has happened world-wide, to cause prices to rise. But it’s so tough to imagine what could possibly account for an increase in inflation in almost the entire industrialized world. It’s not as if these countries had anything in common over the past couple of years.
In any event, this is why I’ve had my fill of U.S. reporting on inflation. It’s just so damned dumb. The endless blather about why it’s due to this, that, or the other uniquely American factor. The constant drumbeat of whom to blame for it. But mostly, the absolute unwillingness to take five minutes, look around, and note that this is not an American issue, it’s a global phenomenon.
Source: Calculated from Federal Reserve of St. Louis (FRED) data, series APU00007471A (gasoline) and CPIAUCSL (CPI), accessed 5/15/2022
In terms of the number of dollar bills you must surrender to purchase one gallon of gasoline, sure, gas is now at an all-time high within living memory.
But, as an economist, I have to point out that a dollar isn’t a dollar any more. It used to be worth quite a bit more. And because of that, it’s just plain stupid to look at long term price trends — or all time highs — in nominal dollars.
In real — that is, inflation-adjusted — terms, the current price of gas in the U.S. is nowhere near at an all-time high. Within living memory. That honor goes to June 2008, when the price of gas in the U.S. hit $5.46 per gallon, in today’s dollars. Continue reading Post #1512: Highest gasoline prices ever? Not really. Not even really close.
Source: Wayfair
The vacuum sealer is that rare device that serves as both a kitchen appliance and a source of entertainment. Every time I run my new Nesco VS-09, I practically want to applaud when it finishes.
I don’t normally give much thought to air. Until it’s all gone. Then the arithmetic of 15 pounds per square inch leads to the realization that this goofy little countertop appliance generates a literal half-ton of crushing force on a 6″ x 10″ pint-sized bag.
But I digress. I actually bought this for the serious purpose of preserving garden produce. The fact that I find the process and results to be so entertaining is just icing on the (perfectly flat half-inch thick piece of) cake.
In any event, there is a serious purpose to this post. And that is to show that if you have a freezer that’s already running, then freezing your tomatoes is by far the most energy-efficient way to preserve them. The only method that would beat that is solar drying, and I haven’t quite figured out how to do that well in my humid Virginia climate.
The last thing I need is another kitchen appliance.
But I bought this vacuum sealer anyway, after thinking through all the food preservation I did last year. Of all the pickling, canning, drying, and freezing, by far, the tastiest, most garden-fresh results came from freezing. With drying (dried tomatoes) a close second, due to the intense flavors that produces.
And so, purely from a quality standpoint, for tomatoes to be used in soups and stews, my wife and I agree that freezing is the best option. It preserves that fresh tomato taste. But how does it stack up in terms of energy use?
Freezing gets a bad rap, as a means of home food preservation, for its relatively high energy use. But I think that’s not entirely correct.
If you run a freezer expressly for the purpose of preserving garden produce, then, sure, I’d bet that freezing has a fairly high energy cost. In that case, you’d have to pro-rate the annual electricity use of that freezer over the pounds of produce preserved. (Because, by assumption, you wouldn’t be running that freezer if you weren’t using it to preserve your garden produce.)
Just tossing out some round numbers, based on past experience, I’d bet that a typical 15-cubic-foot chest freezer has enough space to store 300 pounds of produce, and consumes about 300 kilowatt-hours (KWH) of electricity per year.
So, roughly speaking, if you run that freezer because you use it to preserve your produce, you’d consume about 1 KWH of energy for every pound of produce preserved.
By contrast, if you are already running a freezer, and will continue to run it regardless, and you have the space, then freezing your produce only costs you the energy needed to freeze it in the first place. The cost of running the filled freezer doesn’t count, because you’d bear that cost in any case.
My fridge comes with a big freezer. It’s not like I’m planning to unplug that any time soon. And so, I’m perfectly happy to let my frozen garden produce be a free rider here — taking advantage of the fact that the freezer is running, but not being asked to “pay” for it.
In that case, the only additional energy cost is the cost of getting the room-temperature produce down to the 0 F temperature of the freezer. Given that (e.g.) tomatoes are 94% water, that’s more or less the energy required to bring one pound of room temperature water down to 0 F. Including the one BTU per pound required to cool the water, and the 144 BTUs per pound required to convert to ice, that works out to (70 + 144 =) 214 BTUs, or (at 3.4 BTUs per watt-hour) 63 watt-hours. So, if you are just tossing your produce into a freezer that is going to be running in any case, freezing it takes 0.063 KWH for every pound of produce preserved.
You might think that’s a bit of a cheat, because one way or the other, you’ll want to peel those tomatoes before you use them. The most typical methods for peeling them involve heat (either boiling water, or holding them in the flame of a gas stove). But — surprise — it’s actually a snap to peel them after they’ve been frozen, per this YouTube video.
Take a look around 47 seconds into that video. My jaw dropped just after the tomato did. I know the term life-changing is overused, so let’s just say this was a tomato-life changing revelation for me. As in, I’m never going blanch and peel a tomato ever again. Arguably, it may actually take less energy to freeze-and-peel than to blanch-and-peel, what with the energy costs required to boil the water and cool the tomato afterwards.
I have already tracked the energy costs of preserving by canning or drying, in various earlier posts. Let me bring all of that together in one place, below.
Drying tomatoes in my four-tray Nesco dehydrator consumed 8 KWH of electricity (per Post G21-049). That was in the humid outdoor Virginia summer. I am fairly sure that each tray can hold less than a pound of quarter-inch-thick tomato slices,, but a) I could stack up to 12 trays at a time for drying, and b) those were very “wet” slicing tomatoes, not the paste tomatoes that are normally used for drying. That said, for illustration, let me just assume one pound per tray, four trays, yield 2 KWH for every pound of produce preserved.
Canning tomatoes in a water-bath canner consumes a considerable amount of energy as well. I did the full workup on the energy cost of home canning two years ago, in Post #G22. I had to do that because, as far as I can see, the rigorous research literature on this crucial topic looks like this:
In any case, the all-in energy cost for canning five quarts of pickles, on a gas stove, in an air-conditioned house, was 5528 kilocalories (kcal).
Source: Post #G22.
Per the USDA guide to home canning, quarts of pickles require a much shorter processing (boiling) ,time (15 minutes) compared to quarts of tomatoes (45 minutes) in a water-bath canner.
Based on my prior calculation (shown above), I need to add another 800 Kcal to account for that, bringing the total up to 5300 Kcal for 5 quarts (= 10 pounds) of tomatoes. At 1.16 watt-hours per kilocalorie, that works out to be 0.6 KWH for every pound of produce preserved.
I should note that this is a little conservative, because you have to peel the tomatoes first. That’s going to involve a little additional boiling time. But with all the boiling that’s taking place with the canning, I figured that was more-or-less rounding error.
Finally, I can take a rough guess at the energy cost of my crock-pot spaghetti sauce. Crock-pot spaghetti sauce (Post #G21-048) absolutely minimizes the labor input, and is idiot-proof to boot. But it requires processing tomatoes in both a pressure cooker (briefly) and a crock-pot (overnight). For four quarts (eight pounds), the crock-pot portion uses about 4 KWH. But the pressure-cooker portion (20 minutes at pressure) likely used almost as much energy as canning, so for four quarts I need to add one-third of my pickle canning estimate above, which, by the time all the arithmetical dust has settled, adds another 2 KWH. Or a total of 6 KWH for 8 pounds of tomatoes, or 0.75 KWH for every pound of produce preserved.
Edit, fall 2024: In hindsight, that’s much more energy-intensive than a more traditional reduce-it-on-the-stove approach to making tomato sauce. A crock pot is, in fact, a terrible (but idiot-proof) choice if you want to evaporate water out of a sauce. I’ve gone back to making my spaghetti sauce by boiling down tomatoes on the stove, like a normal person. I still briefly pressure-cook, dump in a strainer to remove the liquid, pass the solids though a Foley mill to remove the skins, then reduce. This allows me to use all types of tomatoes, including salad and cherry tomatoes, without having to peel or seed them first.
There’s no additional energy cost for peeling in this method, because the entire batch of tomatoes is run through a Foley mill after pressure-cooking. That takes out the peels and (most of) the seeds.
Let me now produce the nice neat table of energy required for food preservation, all of it expressed in terms of KWH of energy per pound of produce preserved.
All of that comes with some caveats. The canning was done on a gas stove in an air-conditioned house. The drying was done outside, in humid air. I could dry up to twelve trays at once, instead of the four that I already owned. Maybe there’s a little more energy required for the blanch-and-peel step in some methods. And so on.
Nevertheless, the results are so clear as to be undeniable. (So clear that I double-checked that freezer math a couple of times). If you have space in your freezer, and you’re going to run that freezer anyway, by far the most energy-efficient way to preserve tomatoes is to toss them in the freezer. And, per that YouTube video above, peel them as you thaw and use them.
I surely need to mention the one common method that isn’t on the list, solar (or open-air) drying. Plausibly that has zero energy cost, but I have not (yet) figured out how to do that in my humid Virginia climate. I’m already working on how I’m going to improve my simple $18 plastic-tote food dryer (Post #G21-049). The solution might be as easy as “don’t overload it”.
Two minor factors make this conclusion somewhat less that complete. Those are coefficient of performance (COP) of a freezer, and the different rate of greenhouse gas (GHG) emissions for natural gas and electricity used in the home. Near as I can tell, neither of these results in any material change in the relative efficiency of the various preservation methods.
First, this calculation isn’t complete because it doesn’t factor in the energy conversion efficiency or coefficient of performance (COP) of refrigerators or freezers. The coefficient of performance for a heat pump is the amount of heat energy it can move, for a given amount of electricity supplied to it. Almost all commercially-used heat pumps have a COP greater than 1.0. That is, they can move more than 1 KWH of heat energy for every KWH of electricity they consume. COPs for modern AC or heat pump units typically run around 2.5 to 3.5 (per the link above).
The estimate above — 0.063 KWH — is the amount of heat that needs to be (re)moved from the interior of the freezer. It will actually take less than 0.063 KWH to do that, because fridges and freezers are just another form of heat pump with a COP greater than one. While Wikipedia (cited above) assures me that they have a COP greater than 1.0, I have yet to find a source that will pin that down further. The best I’ve found is a passing reference to a COP of around 1.0 for a deep freeze unit (per this reference).
The bottom line is that a typical home freezer might use somewhat less than 0.063 KWH to remove 0.063 KWH of heat energy from its interior. But how much less, I can’t find the source that will let me pin that down. I suspect that, given the large temperature differential between interior and exterior, the COP of most freezers isn’t much higher than 1.0 or so.
Finally, KWH is not the same as GHG (greenhouse gases). This only measures energy consumed within the home, and does not differentiate between natural gas and electricity. Fossil-fuel based electrical generation is far from 100% efficient, so the actual amount of fuel consumed (to generate the electricity) is a low multiple of the energy actually delivered to the house. But in addition, electrical generation consists of a mix of generation sources, some of which create greenhouse gases, some of which do not. If the ultimate question is one of carbon footprint, we’d have to modify this calculation, treat electricity and natural gas separately, and then redo it for some assumed electrical generation mix.
That said, when I take a rough cut at the difference between natural gas (burned in a stove) and electricity (produced with a typical U.S. generating mix), I’m not sure that adjusting for each fuel type separately would make much difference.
Natural gas releases 100% of its energy within the home. But a typical natural gas stove is only about 40% efficient. That’s the energy that goes into whatever you are trying to cook, with the rest simply serving to heat up the kitchen. Basically, for every 100 units of C02 produced, you get 40 units of usable energy from your gas stove (Whatever units might mean, in this case).
For electricity, by contrast, the amount of fuel burned at the generating plant is far more than the amount that makes it into your home. But once it gets to your home, I’ve either directly measured 100% of what was consumed, or the theoretical calculation (for freezing) should be close to that. And so, as with natural gas, for every 100 units of C02 produced in generating electricity, you get X units of usable energy in the home.
The problem is that X depends on the generating mix that feeds your particular section of the grid. Even so, let me do the arithmetic for Virginia’s electrical grid.
Last time I checked, Virginia’s electrical grid released 0.7 pounds of CO2 per KWH of electricity delivered. Starting from that, I’m going to compare C02/KWH of usable energy for the Virginia grid versus a 40 percent efficient gas stove.
The EPA shows that burning a therm of natural gas releases an average of 0.0053 metric tons of C02. At 2204 pounds per metric ton, that’s 11.7 pounds of C02 per therm. A therm is 100,000 BTUs, and there are 3.4 BTUs per watt-hour.
Slapping that all together, burning a therm of natural gas produces 11.7 pounds of C02 and 29.4 KWH of (heat) energy, or 0.4 lbs C02 per KWH.
But a natural gas stove is only 40% efficient. A stove has to use (1/.40 =) 2.5x as much natural gas to deliver that usable KWH of heat. The bottom line is that a 40 percent efficient natural gas stove releases 1.0 pounds C02 for every usable KWH of heat delivered in the home.
And so, per KWH of usable energy, in terms of GHG emissions, electricity (in Virginia, at 0.7 lbs C02 per usable KWH) is slightly cleaner than natural gas burned in a (typical) 40 percent efficient stove. But only slightly. So the electrical options actually perform a little bit better than shown in the table above, relative to the gas-stove-intensive canning.
There’s nothing in any of that to change the conclusion that tossing your tomatoes into a freezer that would be running in any case is by far the most energy-efficient way to preserve them.
All of the above brings me back to my new toy, the vacuum sealer. If I’m going to freeze my tomatoes, the binding constraint is now the space they take up in the freezer, and secondarily, the length of time they’ll last once frozen. Both of which will be best addressed by vacuum-sealing them.
Most sources suggest that you freeze the tomatoes before vacuum-sealing. But at least one source shows tomato chunks that were vacuum-sealed and then frozen. That’s what I’m now aiming to do, only using whole tomatoes, not chunks. Given the literal tons of force that one of these sealers can generate, I’ll have to use the setting that allows the strength of the vacuum to be controlled manually. In the end, I’m aiming for a freezer stocked with nice, flat, well-preserved packages of energy-efficient frozen tomatoes.
With any luck, we’ll see how that all plays out in a few months.
In my last experiment, I showed how well a Ball (mason) jar worked as frost protection. In the coldest part of the night, the inside of the jar stayed 10 degrees F warmer than the outside. I thought that was exceptional performance for a lightweight uninsulated glass container. My explanation is that the glass traps long-wave infrared. And so, this works for the same reason that my radiant-barrier frost protection works. It prevents the garden bed from radiating heat energy off into space.
Long-wave infrared absorption would explain why glass worked well but polyethylene sheet was a near-total failure. A sheet of ordinary window glass will absorb about 86% of long-wave infrared, and reflect the rest. Polyethylene, by contrast, was reported to be almost completely transparent to infrared.
Accordingly, where a glass jar works well as a garden cloche, I figured that a plastic jar would not. And that’s what I tested last night.
There’s just one problem: Different plastics have different infrared absorption spectra. And it took me a while to track that down.
Using Wein’s Law, the spectrum of radiation emitted by my 50 F garden subsoil would peak somewhere around:
Those are three ways of saying the exact same thing.
So I wanted to find out how different plastics behaved with respect to long-wave radiation somewhere in that vicinity. That’s where most of the power from the upwelling long-wave radiation from the garden bed will be concentrated.
I never did find exactly the data that I wanted. But I came close. And, as it turns out, polyethylene’s absolute transparency in that region of the spectrum is the exception among plastics, not the rule.
The chart below show the absorbance spectra of various common plastics, with the long-wave infrared region highlighted. Note that the line for polyethylene is almost completely flat in that region. It absorbs almost no long-wave infrared. But PETE plastic, just below that, in fact absorbs infrared strongly right at the frequency where infrared from the soil will have its peak — wave number of 1000.
Source: Figure 9, “Identification of black microplastics using long-wavelength infrared hyperspectral imaging with imaging-type two-dimensional Fourier spectroscopy“, Kosuke Nogo, Kou Ikejima, Wei Qi, et al., DOI: 10.1039/D0AY01738H (Paper) Anal. Methods, 2021, 13, 647-659
The upshot is that when I condemned all plastic for this use, I was too hasty. Avoid polyethylene, for sure. But, assuming the glass choche works as I have described it, PETE plastic ought to work reasonably well. Not as well as glass, but certainly not as poorly as polyethylene.
As an odd little footnote, Mylar plastic — the kind used to make space blankets — is the same stuff as PET/PETE plastic — polyethylene terephthalate.
Below is a photo of a quart Ball jar (right) and the thick-walled PETE jar that I’m going to test. That was as close as I could get to the same size and shape as the Ball jar. FWIW, the PETE jar originally held salad dressing. You can see that it’s much thicker than (e.g.) a typical disposable water bottle or soda bottle.
When I tested that last night — two temperature loggers on a raised garden bed, one covered with the PETE bottle, one un-covered — sure enough, PETE works pretty well. But not as well as glass.
At the very coldest part of the night, the PETE jar provided between 4 and 6 degrees F of protection, or about half the maximum protection observed for the glass jar.
The lesson here is that when I condemned all plastics for use in frost protection, I was too hasty. Polyethylene sheet is a terrible choice, from the standpoint of trapping long-wave infrared. But PETE’s OK. Not quite as good as glass, but pretty close.
I took a closer look at the Town’s report on leaf mulching and re-did my table of the vehicle-miles required to gather and dispose of Vienna’s leaves. The conclusion remains the same — all the options require roughly the same number of vehicle-miles. Continue reading Post #1464: Town of Vienna leaf collection: Drive less and pay more is not worth it. Unless you are driving a Prius Prime.
As the Town of Vienna rethinks the economic and human impact of its centralized leaf collection, maybe this is an opportunity to rethink the environmental impact as well.
In this post, I suggest something the Town of Vienna might do to reduce the environmental harm of centralized collection and disposal of leaves.
Briefly: Give equal footing to policies of “put your leaves out for collection” and “better yet, don’t do that”. That is, raise awareness that the most environmentally sound way to dispose of leaves is to let them decompose in your yard. At the same time, make sure that citizens are aware of the substantial harm that centralized leaf collection and disposal does to our local population of butterflies and other pollinators. Maybe offer little “rustic butterflies” to match the “rustic hearts” that are all over town, signifying a household that promises not to rake their leaves to the curb every fall. Continue reading Post #1463: The Town of Vienna and leaf collection: What if we put the environment first?
I saw this headline in today’s Washington Post. It appears that the U.S. CDC is almost ready to maybe sort of recommend that you wear a good mask, not just any mask.
I guess, as pictured above, they’re looking back on the entire history of the pandemic, assessing where we now sit, and asking whether or not they might, possibly, at this stage, as a last resort, recommend an easy, cheap, and effective method for radically reducing the population’s exposure to COVID-19.
Hmmm.
If you read this blog, you know I’ve been strongly in favor of use of high-filtration masks for a long time. Since before the CDC even recommended wearing masks. Just search the “mask” category and you’ll see what I mean
With this latest near-pronouncement from the U.S. CDC, I hardly even know where to start. In the interest of saving time, I’ll skip the rant, and remind you of a few useful things.
1: An N95 isn’t just better than a standard blue procedure mask, it’s vastly better.
2: If you insist on wearing a cheap blue procedure mask, at least learn the “tucked and tied” technique.
3: Leave the KN95s on the shelf.
Here, I’m just repeating a part of Post #938, from almost exactly one year ago.
Here’s a simple question. Even if you think you really, truly understand masks, take 15 seconds to see if you can get the correct answer.
Question: An N95 respirator (mask) filters out 95% of airborne particles. A procedure mask with ear loops filters out about 30% of airborne particles. (That’s based on an actual test of those masks as published more than a year ago in JAMA). Let me loosely call that an “N30” mask. Roughly speaking, how much better is an N95 mask, compared to an N30 ear-loop procedure mask?
The answer is B, it’s 14 times better. Why? The mask rating (N30, N95) shows you what the mask keeps out. But the viral load you inhale isn’t about what the mask keeps out. It’s about what the mask lets through. It’s about 1-minus-the-mask-rating. And in any given situation, the ear-loop surgical mask will let through and expose you to 70% of what’s floating around. While the N95 exposes you to 5%. And 70/5 = 14.
In case you still don’t quite get it, let me do the math the other way. How much better is that N30 ear-loop surgical mask, compared to wearing no mask at all?
Question 2: Assume that you need to inhale 100 copies of COVID-19, at a sitting, in order to get infected. Assume that you are going to inhale one cubic meter of air, at a sitting. How dense can the COVID-19 particles in the air be, before you inhale enough to get infected, based on wearing:
Answer:
Question 2, same math, but rephrased. Suppose there’s a room filled with COVID-19 aerosol. Suppose that, without a mask, you can sit in that room for no more than 10 minutes before you get infected. How much more time does your cheap, blue ear-loop surgical mask buy you? That is, how long could you sit in that room and remain uninfected, wearing an ear-loop procedure mask? And then, how long wearing an N95 respirator?
Answer:
That cheap blue mask buys you a whopping four additional minutes of time, before you get infected. Which not only makes my point, but which shows you why you want to stay away from close, crowded situations, mask or no mask.
Sure, a loosely-fitting ear-loop surgical mask is better than no mask at all. But not by a whole lot, in the overall scheme of things.
I hope you now get why I’m so persnickety about masks. The difference between a good mask and a poor mask isn’t a little bit. It’s a lot. It’s an order-of-magnitude difference in performance.
Still wearing those 20-cent blue procedure masks that you bought a year ago? Can’t bring yourself to pay a whopping 89 cents each for genuine 3M N95 respirators, even though the 3Ms are good for hundreds of hours of normal use before the filter material clogs? Or maybe just just plain don’t like N95s of any sort, despite the wide variety available?
Then you should at least learn the tucked-and-tied technique. By itself, this improves the filtration ability of the typical surgical style mask from roughly an N30 to roughly an N60.
Takes a few seconds to do. Costs you nothing. Doubles the effectiveness of the mask. What’s not to like?
Or watch that directly in YouTube.
The CDC will be doing nobody any favors if they recommend using an N95 or KN95 mask. I’ll go so far as to say that adding KN95 to the recommendation is simply an incompetent mistake.
In the U.S., N95 is a U.S. standard maintained by the U.S. National Institute for Occupational Safety and Health (NIOSH). A NIOSH-certified N95 respirator must fit tightly to the face, using straps that pass behind the head (never ear loops), and, when properly fitted, filter out at least 95% of of the hardest-to-filter particles (0.3 micron).
Masks may then be further certified for medical use by the FDA. Masks certified for medical use must meet additional standards, including resistance to splashes. It is completely possible to have a NIOSH-certified N95 that is not suited for medical use. Most or all NIOSH-certified N95s sold for industrial use — such as the ones you can easily purchase at your local Home Depot or other hardware store — filter to the N95 standard, but are not certified for medical use.
In the U.S., KN95 means nothing. It’s a Chinese standard, and has no legal meaning in the U.S. Anybody can make a mask and sell it as a “KN95” mask.
Practically speaking, in the U.S., KN95 refers to a style of mask, not to a guaranteed level of filtration. A mask that will fold flat, unfold into some sort of cone shape, and use ear loops rather than behind-the-head straps.
I have tried several KN95 masks over the course of the pandemic, and none of them worked well enough to use. They all fit too loosely, allowed too much air to leak around the face seal, allowed my glasses to fog, and were generally insecure due to loose-fitting ear loops.
My point is, the things you can buy in the drug store labeled “KN95” are in no way a substitute for a NIOSH-certified N95 respirator. Not even close. I sincerely hope that some CDC bureaucrats will get out from behind their desks, walk into a few hardware and drug stores, buy a few packs of what are routinely sold as “KN95” masks in the U.S., and assess them for air-tightness and likely filtration ability. And come to the realization that, as I just said, the typical KN95 in America is not even in the same league as a NIOSH-certified N95.
In theory, the FDA had, at one time, a list of certified Chinese manufacturers whose masks could be used in U.S. hospitals under an emergency use authorization. The FDA has long-since cancelled that EUA, and so, technically speaking, there are no KN95 masks certified for medical use in the U.S.
The bottom line is that, for the average consumer, you have no idea what you are buying when you purchase a KN95 mask. For myself, at least, every one I tried failed due to obvious air leaks. And that doesn’t even begin to address the actual filtration ability of the cloth itself, which you have no way of testing, and which was never tested or certified by an U.S. agency.
Maybe if you’ve never worn a properly-fitted N95, you wouldn’t know the difference. But once you’ve worn an N95, and realize that absolutely no air is supposed to leak around the mask, you will instantly reject any hardware-store KN95s on the basis of lack of air-tight fit.
If you must use an ear-loop mask, I’d recommend a made-in-Korea KF94, such as the LG Airwasher. (KF94 is a filtration standard more-or-less equivalent to N95 in terms of particulate filtration.) If it’s genuinely made in Korea, that provides a known filtration ability, and the ear loops are adjustable for tight fit. Of all the masks that I asked my daughter to try, that was by far the most preferred (Post #1246, What mask should I wear? We have a winner).
And at the end of the day, it’s all about wearing the best mask that you are willing to wear.
Over the past two-and-a-half decades, our fall first-frost date has been getting later.
That’s not really a surprise. Global warming and all that. Temperatures are rising slightly in most of North America. Among other things, the USDA hardiness zones have been shifting consistently northward.
The surprise here is the rate at which our first-frost date is changing. In Fairfax County, it’s been getting later at the rate of about one day per year. That may not not sound like much, but it means that our typical first-frost date is more than three weeks later than it was back in the 1990s.
I found that to be a surprisingly rapid change, so I thought I’d post it.
And then, maybe if I’m still feeling the math, I’ll work up the likelihood that this year will have the latest first-frost data on record for Fairfax County, VA. But muse of math seems to have abandoned me, so that will have to be a separate Part II of this post. Continue reading Post #G21-056: First frost date trend and an outdated farmers’ market law in Vienna VA
