4 ms·

The choice to display anything under 35 μg/m³ as "good" does not seem unreasonable at first glance. Indoor PM2.5 can often be higher than outdoor so that the ye

The choice to display anything under 35 μg/m³ as "good" does not seem unreasonable at first glance. Indoor PM2.5 can often be higher than outdoor so that the yearly average will be pushed down by time spent outside and there is no need to have <5 μg/m³ inside too. Also, by the author's admission the unit also measures particles larger than PM2.5 which are less harmful. There's no point in having a unit that will flash orange or red for almost everyone almost all of the time.

ahaucnx 5y ago
As I mentioned in the article it really depends on the length of the exposure and how you use the sensor. Yes in many places in Europe or North America, the outdoor air quality is most of the time good. However -unfortunately- there are also many places where the outdoor air quality is very unhealthy most year round and then an annual exposure to 35 μg/m³ vs 5 μg/m³ makes a big difference.
- aaron695 5y ago
  > the outdoor air quality is most of the time good. This is the point, knowing when it's bad so you can change behaviour? When does it spike in a forest? You'd guess when it's windy? But is it seasonal? Does dust matter more the pollen, I think pollen is more PM 10. Salt from the sea breeze is bad (PM2.5), how does that mix with leaf matter in Fall? > Indoor PM2.5 can often be higher than outdoor so that the yearly average will be pushed down by time spent outside and there is no need to have <5 μg/m³ inside too. This line form OP is totally incorrect. Indoors should be less than outdoors, unless you have a fire or smoke indoors. And why does "yearly average" matter? Smoking cigarettes (which is exactly the same as what we are talking about) is not about a "yearly average".
srg0 5y ago
I think it was a conscious design decision to reduce false alarm rate. Assuming that this low cost device can be/become very inaccurate, then the designers had two choices: 1) Report all alarms as detected. Eventually, the device becomes a red LED which users learn to ignore. 2) Report a problem when the device is reasonably sure there is a problem. Green light does not necessarily mean that the air quality is good, but when the LED becomes red, it should be taken seriously.

ahaucnx 5y ago

As I mentioned in the article it really depends on the length of the exposure and how you use the sensor. Yes in many places in Europe or North America, the outdoor air quality is most of the time good. However -unfortunately- there are also many places where the outdoor air quality is very unhealthy most year round and then an annual exposure to 35 μg/m³ vs 5 μg/m³ makes a big difference.

aaron695 5y ago
> the outdoor air quality is most of the time good. This is the point, knowing when it's bad so you can change behaviour? When does it spike in a forest? You'd guess when it's windy? But is it seasonal? Does dust matter more the pollen, I think pollen is more PM 10. Salt from the sea breeze is bad (PM2.5), how does that mix with leaf matter in Fall? > Indoor PM2.5 can often be higher than outdoor so that the yearly average will be pushed down by time spent outside and there is no need to have <5 μg/m³ inside too. This line form OP is totally incorrect. Indoors should be less than outdoors, unless you have a fire or smoke indoors. And why does "yearly average" matter? Smoking cigarettes (which is exactly the same as what we are talking about) is not about a "yearly average".

srg0 5y ago

I think it was a conscious design decision to reduce false alarm rate. Assuming that this low cost device can be/become very inaccurate, then the designers had two choices: 1) Report all alarms as detected. Eventually, the device becomes a red LED which users learn to ignore. 2) Report a problem when the device is reasonably sure there is a problem. Green light does not necessarily mean that the air quality is good, but when the LED becomes red, it should be taken seriously.