Question: How to interpret PMS5003 sensor values?

samr is asking a question about air-quality: Subscribe to answer questions on this topic

samr asked on April 07, 2019 21:48
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hi. we are trying to use the pms5003 sensor for a school project to take air quality measurements. We don't have much experience with air quality measurements/standards. Can you explain in simple terms what the 12 data values are that this sensor reports back ?

For example, the first 6 are two sets of PM1, PM2.5, and PM10 concentrations. the first set are labeled "standard", while the second set are labeled "atmospheric environment". What do these measure and how do the "standard" ones differ from the "atmospheric environment" ones?

And then there are six particle counts which we are assuming estimate the number of particles of the particular size in a 0.1L volume of air?

Also, how would one take the quantitative readings from the sensor and translate them into some qualitative air quality index scale (like good aq, moderate pollution/acceptable aq, unhealthy for sensitive groups, unhealthy, very unhealthy, hazardous).

thank you very much in advance for any assistance you might be able to offer us!



10 Comments

I think @kkoerner may be able to answer this since he has done a lot of work with this sensor.

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Hi @samr! So great to hear from you. Just to get everyone on the same starting point with this question, I looked up the datasheet for the pms5003 and found it on the website of South Coast Air Quality Management District: http://www.aqmd.gov/docs/default-source/aq-spec/resources-page/plantower-pms5003-manual_v2-3.pdf. On page 13 i found the following information:

  • Data1 refers to PM1.0 concentration unit μ g/m3(CF=1,standard particle)*
  • Data2 refers to PM2.5 concentration unit μ g/m3(CF=1,standard particle)
  • Data3 refers to PM10 concentration unit μ g/m3(CF=1,standard particle)
  • Data4 refers to PM1.0 concentration unit * μ g/m3(under atmospheric environment)
  • Data 5 refers to PM2.5 concentration unit μ g/m3(under atmospheric environment)
  • Data 6 refers to concentration unit (under atmospheric environment) μ g/m3
  • Data7 indicates the number of particles with diameter beyond 0.3 um in 0.1 L of air.
  • Data 8 indicates the number of particles with diameter beyond 0.5 um in 0.1 L of air.
  • Data 9 indicates the number of particles with diameter beyond 1.0 um in 0.1 L of air.
  • Data10 indicates the number of particles with diameter beyond 2.5 um in 0.1 L of air.
  • Data11 indicates the number of particles with diameter beyond 5.0 um in 0.1 L of air.
  • Data12 indicates the number of particles with diameter beyond 10 um in 0.1 L of air

The Asterisk on Data1 and Data4 is defined on the same page as "Note: CF=1 should be used in the factory environment"

There are two questions in your original post that i'd like to direct more people's attention to:

1. What do these measure and how do the "standard" ones differ from the "atmospheric environment" ones?

2. how would one take the quantitative readings from the sensor and translate them into some qualitative air quality index scale (like good aq, moderate pollution/acceptable aq, unhealthy for sensitive groups, unhealthy, very unhealthy, hazardous).

The first i cannot answer, but i'm hoping someone else can.

For the second, let me attempt the start of an answer. An AQI is an Air Quality Index set by a government agency, as stated on https://en.wikipedia.org/wiki/Air_quality_index, "Different countries have their own air quality indices, corresponding to different national air quality standards." From the US EPA site https://airnow.gov/index.cfm?action=aqibasics.aqi :

The AQI is an index for reporting daily air quality. It tells you how clean or polluted your air is, and what associated health effects might be a concern for you. The AQI focuses on health effects you may experience within a few hours or days after breathing polluted air. EPA calculates the AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution (also known as particulate matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. For each of these pollutants, EPA has established national air quality standards to protect public health .Ground-level ozone and airborne particles are the two pollutants that pose the greatest threat to human health in this country.

How Does the AQI Work? Think of the AQI as a yardstick that runs from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 represents good air quality with little potential to affect public health, while an AQI value over 300 represents hazardous air quality.

An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health. AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy-at first for certain sensitive groups of people, then for everyone as AQI values get higher.

Here's a way to begin interactively exploring what generates an AQI reading under the USEPA AQI standards: if you visit this EPA page https://airnow.gov/index.cfm?action=airnow.calculator, and choose the second tab "concentration to AQI" you can experiment with entering your PM2.5 data averaged over 24 hours as shown in my screencapture below or, for other pollutants over other periods of time as specified in the dropdown menu:

AQI.gif

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Here's a link to a comprehensive thread from last year where @sagarpreet was exploring how to visualize a global layer of Purple Air readings. https://publiclab.org/questions/sagarpreet/06-22-2018/what-is-the-correct-aqi-measure

I find the discussion on this thread relevant to your question in the following ways:

  • you can read in here in this comment where @nanocastro advises not to convert a pm2.5 reading into an AQI because an AQI is a particular combination of pollutants, each one of which is averaged over a specific period of time.
  • you can read in this comment as @jeffalk goes into detail regarding the 24 hour averages, and what is known about health impacts after exposure at 24hour averaged levels by health research. He reports that "EPA AQI uses an average of the past 12 hours with an estimation (prediction) of the next 12 hours to assess the air NOW. If you are not able to do that prediction part, you will be misappropriating the risk (health) aspect of the formula and possibly misinforming those you want to communicate with. If you are not able to do the prediction part I maintain you should provide information stating you are using a modified and unassessed version of the USEPA AQI. My suspicion is that PurpleAir does not do this prediction part and, as many people do, takes the most current reading or average over a short period of time, and plugs it into the formula in place of the correct 24 hour past and future average. Whether you use the AQI or particulate density this addresses the color you use and its risk assessment (or actually misappropriation of risk assessment!)"
  • @guolivar observes farther down in the thread that there is no single one right answer and that the essential point to understand is that "AQ indices are designed for COMMUNICATION purposes so the question is not 'should I report concentrations or indices?" but rather "what am I trying to communicate?'" He goes on to articulate that "health effect based" indices try to communicate "risk to people" rather than "state of the air", and that when using indices, "you need to be VERY careful with the averaging times you're using and you need to be very transparent on where you got the calculations from because if you tell people that their air is OK but it isn't, you're in trouble."

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Quickly to your question of: For example, the first 6 are two sets of PM1, PM2.5, and PM10 concentrations. the first set are labeled "standard", while the second set are labeled "atmospheric environment". What do these measure and how do the "standard" ones differ from the "atmospheric environment" ones?

It has to do with the density of the air used for calculations. "Standard" refers to the concentration "corrected" to the "standard atmosphere" which in the US is DEFINED as "having a temperature of 288.15 K at the sea level 0 km geo-potential height and 1013.25 hPa" details here

On the other hand, the "ambient conditions" are just as the air is "now" (whatever temperature and pressure there is) Now what does that mean ...

Air being a gas, it is compressible which means that it changes its volume when the pressure changes so when you report concentrations as mass per volume of air it is relevant at what pressure that volume is calculated. For example, if you have a bunch of particles rising in the air in a bubble (no loss of particles, no addition, they're just riding a bubble up in the air) then, as they rise, the pressure drops so what was 1cc at the ground it is now 2cc so the concentration is now half without anything actually changing other than the ambient pressure. So, it is common to report concentrations (of anything) as "x mg per standard m3" and because we scientist don't like to write much (current example excluded) you'll usually see the "standard" being dropped because it is "implicit".

For gases it is also common to report concentrations as "parts per million" or "ppm" and that metric is independent of the volume of air as it represents the number of molecules of the gas in a million molecules of air (including the target gas) see here the current concentration of CO2

In conclusion, I always use the "standard" readings for reporting but keep the "ambient conditions" for analysis. I haven't used these things in high altitudes so for all my deployments the standard and ambient are very similar.

I hope it helps and I'm happy to be corrected if anyone has information that hints that the "standard" refers to "standard dust" rather than "standard atmosphere".

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Thank you for writing in such an accessible manner @guolivar ! I really appreciate it


Thank you so much for the very clear and helpful information!


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Hi @samr. All the comments above are good and hopefully helpful and your questions are astute. I'm curious as to what led you to "air quality" as a project? and in particular what led you to want to use the PMS5003? When I look at the product manual: http://www.aqmd.gov/docs/default-source/aq-spec/resources-page/plantower-pms5003-manual_v2-3.pdf it looks like a box to me with nothing going in and nothing coming out. Are you technically savvy enough to turn the box into a usable tool? Or are you planning on working with something that includes the pms5003 but is already put together and yields an output that you can change? I believe it would also be helpful to know what level of schooling you are at and an approximate geographic location to be able to refer you to an appropriate governmental department that handles air quality. Thanks.

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We are connecting the pms5003 to an arduino mega 2650 micro controller along with some other sensors such as a BME280 temp, pressure, humidity sensor. The pms5003 was readily available at a reasonable price and seemed to be provide a lot of useful info and easy to communicate with.


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When i read the original poster's question, my takeaway is that this is a student working in a group that has already hooked up a plantower sensor and has begun getting readings, and wants to know more about what they mean.

When i read @jeffalk's comment above, my takeaway is to appreciate this is a very helpful and experienced person interested in providing guidance to air quality inquiries. Another way that the original poster might think about the questions being asked about their project framing could be to visit the https://publiclab.org/issue-brief page, which encourages people to share the "who, what, where, and why" of their issue, as well as perhaps https://publiclab.org/study-design.

As a moderator of this community, I cringed when i read the aggressive question inside of the generally helpful comment that challenged "Are you technically savvy enough to turn the box into a usable tool?" and i encourage us all to keep in mind that Public Lab is a space for people to share skills and knowledge to support one another's work, and to encourage investigation, experimentation, and skill building.

Generally, framing questions and criticisms in a way that helps us all understand each other and our subject matter better is a good start -- for example: offering prompts, suggestions and asking questions when unsure about how someone is approaching a project. This isn't always intuitive or easy, but is a generous way we can engage constructively with one another. Thank you for reading.

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Here's a good overview from EPA Region 1, New England:

https://www3.epa.gov/region1/airquality/pm-aq-standards.html

Although it's a bit jargony.

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