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Air quality reporting on iOS

intergalactic.systems

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Re: Air quality reporting on iOS

#81

Post by crazygringo »

mistercheph wrote: post #80
crazygringo wrote: post #61

Earlier quoted context omitted.

Really not sure what your point is? The temperature and humidity values that iOS Weather reports are objective and "dispassionate", no? Likewise wind speed and so forth? AQI is unique in this case, in that it is a color-coded interpretation of combining multiple underlying objective values (PM2.5, etc.). And different governments have chosen different official national schemes for this, according to what they want th…

No, they are neither objective nor dispassionate, despite being grounded in empirical data and methods. Factors like building shade, vehicle density, wind cover, terrain, cloud coverage, and variations in humidity, mean that thermometers placed at different points in any selected area will report massive variations in temperature, and the naive (and impossible) approach of even distributions of identical sensors taki…

You make a good point that the phone isn't (usually) reporting a direct measurement, but is rather interpolating weather station temperatures for a single coordinate. (And cities generally have a single lat/lon "center" for weather reporting, although your iPhone will attempt to report the weather for your location rather than the nearest city's center.)

But nevertheless, a correct, objective, dispassionate temperature reading for that coordinate does exist in reality. And the phone's weather service is trying to approximate that as closely as possible. And you can objectively measure the error to improve future models.

My point is still that this is qualitatively different from composite air quality indexes, which are politically designed, and therefore designed differently for different countries.

Re: Air quality reporting on iOS

#82

Post by mrob »

apwheele wrote: post #41

Of interest to folks looking at this post -- Chris Said has a deeper dive on US air quality metrics and their provenance, https://chris-said.io/2023/06/19/the-air-quality-index-doesn... . The attempt to make things easy to interpret using a nice relative scale ends up in the end make them very opaque to interpret the number itself in any meaningful way.

The "inexplicable" addition of 0.4 to the round multiples of 50 looks like it's there to stop people claiming that limits apply after rounding to the nearest fifty.

If the threshold is 50, people might claim 74 is acceptable because it rounds to 50. If the threshold is 50.4 this is obviously false.

Re: Air quality reporting on iOS

#83

Post by rodgerd »

crazygringo wrote: post #61
brookst wrote: post #51

Earlier quoted context omitted.

Many products have multiple stakeholders. I can't think of a single product that exists "to render dispassionate information" and nothing else.

Really not sure what your point is? The temperature and humidity values that iOS Weather reports are objective and "dispassionate", no? Likewise wind speed and so forth? AQI is unique in this case, in that it is a color-coded interpretation of combining multiple underlying objective values (PM2.5, etc.). And different governments have chosen different official national schemes for this, according to what they want th…

> The temperature and humidity values that iOS Weather reports are objective and "dispassionate", no?

You sound like someone who has never lived anywhere that people bitch and moan about the temperature on the weather reports being wrong because people think it's warmer than weather stations report, and get into arguments that the weather stations aren't placed correctly.

Re: Air quality reporting on iOS

#84

Post by teekert »

I live in the Netherlands, I've tried to get this air quality report out of the iOS app, so have others. It just tells me every day the air is shit. I mean when you tap on it, it tells you not to exercise outside for example. It's rarely "good", mostly it is "insufficient", sometimes it's "very bad".

Is it really so bad? You don't hear anything about it from other sources... Tapping on, one finds the main pollutant to be ozone, "usually caused by traffic and it can be transported over large distances."

Idk what to think of this. Many people seem confused. Are we really in such poor air all the time?

Sometimes I bike through the fields in the morning, sniff the fresh humid air that has a coldness in it, I smell grass and flowers... Apple tells me: Insufficient (don't bike to fast!) :(.

Maybe they are right, maybe they are forcing us to come to terms with the things we do to our air.

Re: Air quality reporting on iOS

#85

Post by counters »

crazygringo wrote: post #74
counters wrote: post #62

Earlier quoted context omitted.

Eh, kriging is overkill relative to the skill you end up with since fine-grain spatial variability in weather can arise from a lot more than the static factors you can pull into such a scheme. This is why objective analysis techniques are typically preferred. More importantly, high-resolution priors are universally available from weather models, so there is no need to just to ever naively interpolate between weather…

I'm curious if you could expand -- I researched this a while ago but what I'm describing is as deep as I got from various online tutorials. What kind of objective analysis techniques? And where does someone get high-resolution priors from? Are you saying that companies have gone out and done a one-time mapping of temperature etc. at a e.g. 1-mile grid across the US? (Which would be over 3 million points at that scale…

Probably the two most common and simplest are Barnes and Cressman interpolation (see [1] for a modern implementation of Barnes), which use inverse distance weighting to combine observations within a neighborhood. An improvement to these techniques frequently used to grid statistical weather forecasts is the BCDG method (see [2]).

The core idea of any objective analysis/interpolation scheme is that you model spatial relationships with some sort of function. Kriging exemplifies this - you fit a spatial covariance model and use that to predict values in the far field, using combinations of nearby values. I don't really have a good link or textbook reference at arms reach, but you can quickly re-frame this entire interpolation problem as a data assimilation one where you're attempting to approximate a solution to some 2D or 3D field using sparsely sampled observations; in the weather world, the Real-time Mesoscale Analysis used in the USA is a good example of a system which hybridizes a weather model and observations to create a high-resolution analysis [3].

A problem arises when the field you're analyzing can have shocks or variability much smaller than the scale that you're able to measure from your network. A front is a great example - across a front, temperature and wind direction will change over a very small distance, but most interpolation schemes will smear this out. The problem is that you really do care about that front and its location - that's where the interesting weather happens!

> And where does someone get high-resolution priors from?

A high-resolution weather forecast model, which uses physics to simulate the atmosphere and produce reference states. 3-km forecasts are readily and easily available in the US.

> Are you saying that companies have gone out and done a one-time mapping of temperature etc. at a e.g. 1-mile grid across the US?

No, this probably wouldn't be useful. Especially because we get a ~1-km mapping of lower troposphere temperatures from geostationary weather satellites every 10-15 minutes across the entire globe. May not be exactly "surface temperature", but it tells you a whole lot about high-frequency variability in temperature fields.

[1]: https://gmd.copernicus.org/preprints/gmd-2022-116/gmd-2022-1... [2]: https://journals.ametsoc.org/view/journals/wefo/24/2/2008waf... [3]: https://journals.ametsoc.org/view/journals/wefo/26/5/waf-d-1...

Re: Air quality reporting on iOS

#86

Post by counters »

908B64B197 wrote: post #78
counters wrote: post #64

The problem here is twofold. First, many countries have their own laws and policies regarding air quality exposure. Often times these regulations use metrics about time-average exposure (e.g. the annual average 8-hr maximum ozone concentration) and can't trivially be converted between agencies. It causes very negative user experiences when your air quality summary disagrees with what a regulatory agency is putting ou…

> many countries have their own laws and policies regarding air quality exposure. Often times these regulations use metrics about time-average exposure (e.g. the annual average 8-hr maximum ozone concentration) and can't trivially be converted between agencies. It causes very negative user experiences when your air quality summary disagrees with what a regulatory agency is putting out to the public due to a measureme…

> Ultimately, why not simply compute it and give the user a warning that the local measurement isn't compatible with proper AQI measurement?

You totally could, but in practice it doesn't always or obviously lead to a positive user experience our outcome.

Re: Air quality reporting on iOS

#87

Post by crazygringo »

counters wrote: post #85
crazygringo wrote: post #74

Earlier quoted context omitted.

I'm curious if you could expand -- I researched this a while ago but what I'm describing is as deep as I got from various online tutorials. What kind of objective analysis techniques? And where does someone get high-resolution priors from? Are you saying that companies have gone out and done a one-time mapping of temperature etc. at a e.g. 1-mile grid across the US? (Which would be over 3 million points at that scale…

Probably the two most common and simplest are Barnes and Cressman interpolation (see [1] for a modern implementation of Barnes), which use inverse distance weighting to combine observations within a neighborhood. An improvement to these techniques frequently used to grid statistical weather forecasts is the BCDG method (see [2]). The core idea of any objective analysis/interpolation scheme is that you model spatial r…

Thank you so much, that's all so fascinating! And makes perfect sense that priors come from high resolution physics solutions.

Much appreciated for all that info.

Re: Air quality reporting on iOS

#88

Post by esafak »

teekert wrote: post #84

I live in the Netherlands, I've tried to get this air quality report out of the iOS app, so have others. It just tells me every day the air is shit. I mean when you tap on it, it tells you not to exercise outside for example. It's rarely "good", mostly it is "insufficient", sometimes it's "very bad". Is it really so bad? You don't hear anything about it from other sources... Tapping on, one finds the main pollutant t…

Sounds like a bug. I don't recall the Netherlands having bad air; it's pretty green. I wonder how this can be reported?

Re: Air quality reporting on iOS

#89

Post by calsy »

crazygringo wrote: post #61
brookst wrote: post #51

Earlier quoted context omitted.

Many products have multiple stakeholders. I can't think of a single product that exists "to render dispassionate information" and nothing else.

Really not sure what your point is? The temperature and humidity values that iOS Weather reports are objective and "dispassionate", no? Likewise wind speed and so forth? AQI is unique in this case, in that it is a color-coded interpretation of combining multiple underlying objective values (PM2.5, etc.). And different governments have chosen different official national schemes for this, according to what they want th…

Air quality is not a weather measurement like temperature or humidity, far from it. Air quality is greatly influenced by human activity and is an extremely contentious issue in many countries.

Re: Air quality reporting on iOS

#90

Post by calsy »

jsjohnst wrote: post #22
evanriley wrote: post #15

Earlier quoted context omitted.

Hmm, what country does this happen in? I've never seen it use Low/High, only from Good to Hazardous.

Same for me in US English. For example, right now it’s “18 - Good”. It was “469 - Hazardous” just three weeks ago though.

Happen to have any large fires nearby?
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