Hi,
I'm searching some Air quality sensors like how much air is actually breathable (%), well
mostly the quality and amount of the actual air around the sensor to see if it's possible to breath
or not in a unknown environment. Any known small sensors that can detect that?
or
Is there any kind of sensors that can detect more than just air? Like what kind of gas is in the air or stuffs like that?
Thx
D60
I think that what you want to do would take a mass spectrometer. I don't think they are available in chip form yet. 
Any other air quality sensors? I found "MQ 135" :
The MQ-2 is suitable for detecting LPG, i-butane, propane, methane, hydrogen and even smoke.
The MQ-5 detects LPG, natural gas and town gas.
How exactly is the data displayed? Let's say we got MQ-2 and there is propane in the air how exactly will be displayed?
I'm mostly looking for a sensor that will display how clean is the air and if not then what kind of gasses and how many % of that gas is in the air, for example if you are close to a factory I wanna know how much of waste "air" they pollute (air pollution) of something like that.
D60
gotta get your specs in a solid form, you are floatijng around.
first it was 'breatheable' or how much O2,
oxygen is usually the only metabolically active component
then it is a specific gas sensor 'propane'
then how clean aka how dirty the air is..
then how much of an un-defined quantiy the air contains.'pollution'
i suggest you study up on the available sensors and work out the chemistry that separates them. many overlap.
also, read what 'air' is. air is air. air with pollutants is air plus pollutants, it is not just air.
read up on partial pressures. this is key to understanding why sensors work. essential really.
once you get a grasp on what the sensors can do they will make much more sense.
There are sensors like that for a number of gasses and vapors. They don't 'display' anything. They change resistance with the concentration of contaminant, but the zero-point resistance varies widely due to manufacturing tolerances so they are supposed to be calibrated against a known concentration. They also tend to be sensitive to multiple pollutants and have a different sensitivity curve for each so unless you know you have only one pollutant and you know WHICH single pollutant is present you won't be able to calculate the concentration (parts per million).
Note that each of these sensors has a heater which draws a fair amount of power (~800 mW) and, if I recall correctly, those heaters have to be running for 24 hours before you can expect to get stable readings. Neither of these limitations is good for a portable instrument.
These sensors are also sensitive to temperature and humidity so to get accurate results you will probably want to measure those and correct for the offsets
This page links to the datasheets for a large number of gas sensors:
http://www.china-total.com/Product/meter/gas-sensor/Gas-sensor.htm
Study the datasheets, particularly the sensitivity curves.
Basically there is no sensor that does this directly and all the projects I have seen that think they are measuring air quality are not.
These sensors are only remotely accurate if they are calibrated about once a month with a known concentration of a specific gas. Even then other pollutants do affect the reading for all the sensors.
As mentioned you need a mass spectrometer to do this. Of courses in Si-Fi this is an everyday hand held sensor but real life is not like that.
Note that each of these sensors has a heater which draws a fair amount of power (~800 mW) and, if I recall correctly, those heaters have to be running for 24 hours before you can expect to get stable readings. Neither of these limitations is good for a portable instrument.
Well that's a really big problem in my case, i need to draw low power and make it work in few sec.
These sensors are only remotely accurate if they are calibrated about once a month with a known concentration of a specific gas. Even then other pollutants do affect the reading for all the sensors.
As mentioned you need a mass spectrometer to do this. Of courses in Si-Fi this is an everyday hand held sensor but real life is not like that.
Well I need some kind of "air quality" sensor, isn't there any kind that will work with low power and directly without waitting the calibration or anything else?
Well if you have any kind of sensor in your mind please tell me or give an idea how i could make what i need. I will keep searching too.
Thx,
D60
Hi D60,
I am running a similar project to measure air pollutants so I would like to know if you have figured out which sensors to use and how to use them. I would like to measure O3, NO2, SO2 and NH3.
Many thanks
All the electrochemical sensors mentioned above aren't very specific. The respond to many gasses apart from the one they're nominally most sensitive to. They can also be 'poisoned' - ie certain pullutants will make them much less sensitive.
If you want sensitive specific accurate devices, suggest you start off with a cheap mass spectrometer and a catharometer based photoionisation detector. Start at around £100,000 I guess. Running these devices takes some skill, as does the interpretation of the results. A degree in chemistry is useful ( essential?) here.
Or take an air sample to your local government lab , which has all the gear.
In England he/she's called the 'public analyst'.
regards
Allan.
an electro chemical sensor can be element specific. that is it can detect CO and ignore Co2 and C and O. to get this specific gas sensing, the chemical brew is relatively unstable and reacts to the specific gas.
expect to pay over $100, $250 for the liquid filled container. often lasts up to one year if not in a high concentration environment. the chemicals react with the specific gas and are used up while in operation.
The hobby variety we see on e-bay for a few dollars are low cost, but broad spectrum and cannot single out any specific gas or elements. often you just want to know if there is any air pollutant.
as you pay more, you get lower energy consumption. the Figaro units are often less than $50, but use much less power.
the newest types are the MEMs or Microelectromechanical.
A MEMs like the BME680 are hard to find and are tiny and use so little power that they might last a year on a battery. much harder to get. Philips announced they started manufacturing the beginning of last year, they have yet to get into our food chain. probably being bought up faster than they can make them by big industry. air fresheners want them as the basis of spraying VOC's into your environment to mask the odours. or give you that outdoors odours.
I bet a CO sensor would also be very sensitive to HCN - they've a smilar electronic 'shell' to them..
And I reckon I could find an interferer for all the common gasses.
Depends what you expect to find - and what's in there you didn't.
regards
Allan