[HN Gopher] An air quality model that is evolving with the times
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An air quality model that is evolving with the times
Author : Brajeshwar
Score : 99 points
Date : 2024-05-28 14:22 UTC (8 hours ago)
(HTM) web link (eos.org)
(TXT) w3m dump (eos.org)
| culi wrote:
| > Since its creation, STEM has evolved to cover a broader set of
| key air pollutants, such as ozone and particulate matter,
|
| I've always found air quality metrics focusing on particle size
| confusing. E.g. PM2.5 (which describes fine inhalable particles,
| with diameters that are generally 2.5 micrometers and smaller)
|
| But surely there must be a massive qualitative difference between
| particulate matter of, e.g., lead vs particulate matter of, e.g.,
| pollen or fungal spores, right? How useful is it really to lump
| all of these together?
| londons_explore wrote:
| Indeed - clearly it matters what the particles are made from.
| Some stuff won't even be toxic, like particles of water (fog).
| jvanderbot wrote:
| Yes - there are other poisons as well hidden behind those
| particles, but it's _very_ hard to measure the composition of
| those particles in real time. Particulate matter _can_ be
| measured with a $20 sensor from Sparkfun, so it 's an often-
| used proxy.
|
| As for why the particles sizes are differentiated, I think it's
| because some sizes can cross barriers into the blood - and are
| therefore concerning regardless of the contents. pm 2.5 can
| reach the deepest parts of the lungs and just muck up that
| whole area regardless and cause all kinds of systemic
| inflammation. pm 10.0 generally doesn't reach that deep but
| still causes eye/ nose/ throat problems IIRC.
|
| If there is near-zero or undetectable particulate matter, then
| that would preclude lead particles as well, obviously.
| culi wrote:
| This seems like a reasonable explanation, thanks
| taeric wrote:
| I mean, yes, toxins in the air are worse than non-toxins in the
| air. I don't think anyone will really debate that.
|
| The banal answer to your question is you measure what is easy
| to measure. And it is easier to build a device that can measure
| size of particles than one that can enumerate all of the types.
| Especially since you will take the same actions regardless? Put
| up a filter and run it.
| hollerith wrote:
| >Put up a filter and run it.
|
| It's not that simple because any filtration media that will
| filter out, e.g., diesel exhaust or pollen will lyse the
| bacteria that are always floating in the air, thereby adding
| to the air that leaves the filtration device the
| lipopolysaccharide (LPS) toxin that without the action of the
| filtration device would remain relatively-safely inside the
| bacterium. Yes, even without any air purifiers, you will
| absorb some LPS toxin from the bacteria in the air you
| breath, but running an air purifier approximately doubles the
| dose. I claim to be able to tell the difference in that when
| I'm in a small room with an air purifier running at high fan
| speed, I am much more likely to feel a certain kind of non-
| severe, but not-good headache-like feeling.
|
| I.e., you don't want to run an air purifier that removes very
| small particles from the air when you don't need to -- at
| least if you are as sensitive to LPS as I am. And you don't
| want the fan speed of the purifier's being higher than
| necessary.
| InitialLastName wrote:
| I'm gonna need a source on that, as the only relevant thing
| that comes up on a search for "lipopolysaccharide toxin air
| filter" is a single study [0] that tested a single air
| purifier (whose filter had not been changed in a year) in a
| single room. It includes the telling phrase: "The
| conclusions here, however, should be interpreted cautiously
| due to the small sample size here."
|
| [0] https://www.sciencedirect.com/science/article/pii/S0160
| 41202...
| hollerith wrote:
| >I'm gonna need a source on that
|
| Sadly, I was unable to find a link to the study I got my
| info from after searching my notes for about 7 minutes.
| taeric wrote:
| It can be more complicated, yes. I assert that it usually
| isn't. You don't spend time worrying as much about what the
| contaminants are, you just drive them to zero.
|
| I grant the point that you don't want to just stir up the
| air. Which is why you don't just run a fan, necessarily.
| nonamousnoose wrote:
| They are separated by size because that determines which
| airways they migrate to, and which can enter the bloodstream.
| Yes, what they're made of matters - the latter is also measured
| in specific studies, but the former is a lot easier/cheaper to
| systematically measure.
| wnevets wrote:
| Focusing on PM 2.5 makes sense because anything that size and
| smaller tend to cause the most harm. [1]
|
| [1] https://www.epa.gov/pm-pollution/particulate-matter-pm-
| basic...
|
| > Particulate matter contains microscopic solids or liquid
| droplets that are so small that they can be inhaled and cause
| serious health problems. Some particles less than 10
| micrometers in diameter can get deep into your lungs and some
| may even get into your bloodstream. Of these, particles less
| than 2.5 micrometers in diameter, also known as fine particles
| or PM2.5, pose the greatest risk to health.
| BobaFloutist wrote:
| Presumably smaller particles are also more difficult to
| filter (and therefore more likely to make their way indoors
| without dedicated filtration), and also expected to remain
| airborne for a greater distance and duration (because of
| square cube things).
| hedgehog wrote:
| PM2.5 is around the hardest size to filter, I don't
| understand the physics but both larger and smaller are
| actually easier to remove from the air. Given that 2.5 is a
| useful estimate of worst case performance for a given
| setup.
| TylerE wrote:
| Basically a HEPA/electrostatic filter works in two ways.
|
| As a "physical" filter (think fishing net), works well on
| big particles.
|
| As an electrostatic filter, works best with really small,
| works by electrically attracting particles and having
| them stick.
|
| 2.5 micron is in the middle crossover range where total
| net effectiveness is worst. Respirators are rated at the
| same size for the same reason.
| LordDragonfang wrote:
| >Presumably smaller particles are also more difficult to
| filter
|
| So, that may or may not be true for just passive filtering
| (like door and window frames), but it's actually not true
| for actual hepa-style filters, because the physics of
| particulate filtering is totally unintuitive from the macro
| level -- past a certain point, finer particulates actually
| become easier to filter, because the physics is dominated
| by two different effects at different sizes.
|
| https://dynomight.net/ikea-purifier/#on-physics
| 4death4 wrote:
| Yes, but isn't lead getting into your bloodstream worse than
| pollen? I mean oxygen gets into your bloodstream via
| inhalation...
| bluGill wrote:
| Worse in what way? Lead is a long term neurotoxin, but
| pollen triggers the immune system and makes you miserable.
| Both are bad but in different ways.
| 4death4 wrote:
| It's really unclear to you why a long term neurotoxin
| that leads to lifelong disability is worse than allergy
| producing pollen?
| bluGill wrote:
| It isn't clear until you are suffering from allergies,
| and notice that old people who used to chew on lead
| fishing weights are not all that bad off. Most people
| with high lead in their bodies don't realize the issue
| nor to the people they know.
| alright2565 wrote:
| > used to chew on lead fishing weights
|
| Chunks of lead just aren't that bad.
| https://doi.org/10.2146/ajhp060175 lists common sources
| of lead poisoning, and none of them are lead weights.
|
| Common sources involve things like airborne lead powder
| (from grinding or smelting), lead compounds dissolved in
| food & water, paint, and lead in soil.
| wnevets wrote:
| Which plant produces pollen at PM2.5 tho? Pollen usually
| isn't entering your bloodstream through your lungs, its too
| large.
| semi-extrinsic wrote:
| Pollen particles are quite fragile and tend to break up
| into PM2.5 and smaller, especially during rain events.
| See for instance the reference below.
|
| https://doi.org/10.1016/j.aeaoa.2022.100177
| culi wrote:
| In addition to pollen, there are spores from both
| mushrooms and ferns. Both of which are common cloud-
| seeding particles and can often be PM2.5
| tomrod wrote:
| Most pollen is captured at pm10 or higher level. PM2.5
| tends to be created by humans
|
| Crossing the blood brain barrier exacerbates not only
| asthma but other vascular/heart and related diseases,
| including diabetes, as well as lung diseases.
| BunsanSpace wrote:
| Canada is updating their model to be the worst of PM2.5 and
| their traditional models of common pollutants.
|
| Part of the issue is the existing model does an average over 3
| hours, where PM2.5 can change rapidly (fire, traffic surge,
| &c). So they have a second metric that is averaged over an
| hour.
| photochemsyn wrote:
| Getting the data on the chemical composition of the PM2.5
| fraction of air pollution requires fairly advanced
| instrumentation and lab capabilities. It is the important data
| in estimating toxicity, for example:
|
| https://meetingorganizer.copernicus.org/EGU24/EGU24-881.html
|
| > "It was found that PM chemical composition was major
| determinant in toxicity assessment rather than its mass
| concentration."
| luma wrote:
| PM2.5 is of interest because it's a size that your body has a
| harder time getting rid of. Larger size particles have an
| easier time being captured by the upper respiratory system.
| Smaller things might make it into the blood stream and
| hopefully be filtered by the kidneys. 2.5 microns is right at
| the point between where either thing is less likely to happen
| and instead the stuff might get stuck in your lungs.
| geniium wrote:
| We don't need a model, we need to take care of our planet.
| culi wrote:
| We don't need passwords, everyone just needs to be nice to each
| other
| BobaFloutist wrote:
| California wildfires are an important, natural part of the
| ecosystem, but I still like to know when it's worth wearing an
| N95 mask and turning on my air filter to prevent that
| important, natural part of the ecosystem from permanently
| damaging my lungs.
| anonporridge wrote:
| We don't need lightning rods, we just need to pray to Zeus.
| Spivak wrote:
| Steelmanning the parent's argument. Having a better model of
| how fucked we are when there there's no appetite to actually
| do anything about is high-effort doing nothing.
| thfuran wrote:
| But if you don't have a good model, you can't reliably
| identify the good ways of unfucking.
| waveBidder wrote:
| The first step in getting people to care is proving there's a
| problem, and accurate models help with that. Not as much as
| actual data mind you.
| hendler wrote:
| Air quality is not thought enough of in terms of localized data.
| Some modeling works at larger scales, but if you want to know the
| forecast for other pollutants (especially ones that disperse or
| transition) or the source of methane leaks, you need very
| localized data from many modalities (wind direction, temperature,
| topographic, seasonal, traffic, etc).
|
| I worked at https://aclima.io on air quality for 6.5 years. My
| role was managing backend data pipelines, but I worked with
| scientists and data scientists who were pushing the boundaries of
| models' capabilities. Models are complex and expensive - any
| advancement here, like Graphcast, is very important. [1] One job
| our team was responsible for is to reduce the cost of high
| quality data, so we drove vehicles around to collect very
| localized data, which ended up being temporally sparse. Modeling
| can fill gaps to some measurable level of certainty.
|
| It should also be said that policy is far behind the science, but
| the burden will remain on science and data to continue make
| conclusions irrefutable.
|
| [1] - https://deepmind.google/discover/blog/graphcast-ai-model-
| for...
| selimthegrim wrote:
| Is there a good email address/way to reach you? I have a couple
| questions about your past job as well as the product at your
| current gig.
| banish-m4 wrote:
| The costs of changing from say a model like the US EPA AQI to
| something else is it creates fragmentation and breaks
| comparability and infrastructure that came before. An agreed-upon
| international "AQ" metric should reflect real risk to sensitive
| groups and long-term health outcomes.
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