When I read the HN article title, I knew which domain it'd be from before I saw it.<p>I have several AirGradient devices and they've been great, no hassle at all with my own software instead of cloud-connected anything. I just wish there were a really good CO monitor that was also no-pain.<p>Thanks for making a product that sells on its own merits instead of forcing ecosystem lock-in or trying to obscure what the thing is or does.
I really love the spirit of AirGradient and their products.<p>However they are shooting themselves in the marketing foot by not doing free datastorage for life for their users and therefore competing with PurpleAir which is the closed premium they are competing against.<p>Google has chosen PurpleAir for their map overlay for air quality, it shouldn't be that exclusive but the reason why is the sheer number of installs.<p>compare for your area:<p><a href="https://map.purpleair.com/" rel="nofollow">https://map.purpleair.com/</a><p>vs the emptiness of<p><a href="https://map.airgradient.com/" rel="nofollow">https://map.airgradient.com/</a><p>I keep telling them they need to just GIVE FOR FREE their units to all public universities in the United States with free data for life reporting, it will change their entire company's presence in the USA and maybe even make Google add them.<p>Right now many universities, firehouses, stadiums, etc. etc. use WeatherStem for local weather recording/reporting. You know what WeatherStem does NOT have? Air Quality recording/reporting. Imagine if AirGradient gave their units to all the major WeatherStem sites that already have power and internet setup.<p>look at the pulldown for the WeatherStem open-source data export and imagine AirGradient added for air quality to ALL those hundreds of universities<p>export pulldown <a href="https://forsyth.weatherstem.com/data" rel="nofollow">https://forsyth.weatherstem.com/data</a><p>breakout (<a href="https://forsyth.weatherstem.com/" rel="nofollow">https://forsyth.weatherstem.com/</a>)
Our lab build and characterized one of the first low cost mobile PM sensing devices and worked with a major manufacturer of reference devices. I think the article is partially over simplifying. This is because also the reference devices do some tricks to derive mass concentration. Real mass concentration can only be measured at a low frequency by using actual filters that absorb the PM in the correct size category. Optical and beta attenuation devices are actually calibrated. The question is if the translation of absorption and count is actually so stable against mass. If you use other types of sensors like nephelometers you can for sure get different readings, however: are they really more wrong? Particularly if due to the measurement pricinciple a higher resolution is in the data. If you would want to measure mass concentration you would need to compare against real mass concentration and aggregate values. I am not sure if high resolution RSME is really helpful as a metric here. Constantly in place calibrated low cost sensors are often quite good. But this does not tell so much about their quality. In the end it is what you want to do with the sensor. For regulatorybpurposes (measuring e.g urban background) the placement of the sensor is often more important than the accuracy. If you want to discover relative and transient effects a well calibrated network of dense low-cost sensors might be a fit. In the end you cannot even easily translate exposure to harm, because it the material of your PM very likely will also matter (we are just assuming the typical mix in most cities when deriving limits)
I appreciate the focus of the article and the explanations laid out for us. I would like to point out though that the two photos used as the "Less Polluted" and "More Polluted" examples may not fit the descriptions.<p>Less Polluted shows a point in a city after a rain shower. The passage of a storm front tends to leave the air behind it more clean that it was before it arrived. That example makes the most sense.<p>More Polluted does not make sense when you look at the photo since it obviously shows a storm front making it's way across a city, maybe the same one in the "Less Polluted" example. That storm is cleaning the air as it passes and the buildings in the foreground look like the storm has already passed. To me that means that the air from the photographer's vantage point should be clean already. It isn't possible to know whether you are looking east at dawn or west at sunset but either way that storm has passed, bringing clearer air to the city.<p>A better example would be a photo of that same city on a cloudless summer day when the air is choked with smog and those who care are wishing for a nice storm like the one pictured to sweep through and clean it all up.
I'm glad to see there's an alternative to Airthings. The problem with them is they should be calibrated at least every year but they can't be, so they just deny that they ever go wrong and pretend the problem doesn't exist.
I hope it's okay to ask this question. For you that have these sensors, what actions do you take based on what they tell you? Open more windows when you're cooking? Put on a mask when you vacuum?<p>Just curious.<p>I've dreamed of some future perfect portable sensor like a star trek tricorder or something that would tell me if the air in my office, or shopping center has bad stuff in the air (chemicals, viruses, mildew, etc...) to some point that I can print out a reading and tell my office the building is legally unsafe. I haven't seen anything like that.<p>I have sensor at home but all it tells me is PPM and I rarely pay attention.
> Yet, you would probably go for the <i>right</i> sensor, true? That’s because this one has a lower relative error.<p>If the author is about, I have a feeling this should read <i>left</i>?
I recently bought one of their monitor, and I'm pretty happy with it. It was the only one that provided CO2, PM2.5 and VOC at my price point. They were also tested by the agency in charge of monitoring the air quality in Paris, so I can reasonably trust their monitors at the difference of most of the non pro ones. I only wish there was a possibility to store the data on a micro SD card.
Based on the title, I was expecting this article to have instructions for calibrating an air quality sensor, rather than just explaining different error types.
Ok, so you compare your sensor to a reference sensor. But...<p>> If you compare two reference instruments, they should ideally measure exactly the same, namely the true pollutant concentration. But they don’t: A study from the US-EPA co-located two commonly used reference instruments (Met One BAM-1020 and Teledyne API T640) and found that, at certain concentration ranges, they diverged by over 25% from each other.
Have experimented with this too - the accuracy is less of a concern to me than the fact that PM sensors require airflow and most achieve that via shitty whiny tiny fans. bzzzzzz<p>Closest "solution" I've found is the airsensors built into some airfilters. They seem to steal some of the main airflow rather than having a second fan. Obviously not quiet but at least fan size is decent so bit lower pitch<p>As for other measurements - for temp/humidity/pressure...any sensor will do. CO2 - the SCD41 are best I've found, BME680 and BME688 are hot garbage.
I have to admit I was a bit disappointed that the conclusion was effectively diff your sensor with a reference sensor, I was hoping it was more like "here is how to make your own reference measurement".<p>Don't get me wrong it was a good article, I appreciate the math on how to make a meaningful diff.