[Wearable] LeAirf – Air Quality Detection Necklace

A wearable necklace indoor air quality detector with a mobile display app. 


necklace, wearable, BLE, bluetooth, air quality, AQI, phonegap, physical computing, cordova, nodejs, rfduino,

Board design: Jiashan Wu
The rest: me


  • Personal Statement

I suffer throat problem since very young. I realized it is due to the super pool air quality where I was living. When I moved to NYC, I thought at least my throat problem could be alleviated a little. Unfortunately it still remained the same level after 9 months. I wonder why because AQI in the two countries/cities are absolutely different, even NY is relatively severely air polluted in US.  The question may be solved when a student told me that the air quality at ITP is as the same level as in Beijing. We have a shop where a great amount of particles are produced and we do not open window often to let fresh air comes inside.

So I want to narrow down my project topic to be an air quality detection device for personal use.  To let people be aware of the problem and take care of the environment they are in.

  • Background– indoor air pollution

When we talk about air. There are two types of air quality that we usually use: Ambient Air Quality(outdoors) and Indoor air quality. I began to think about what is the air problem in US rather than in China. So I can do something to solve problems here as well benefit back to China. And I found the common problem is the indoor air quality.
According to EPA, the average American spends 93% of their life indoors.  87% of their life is indoors, then another 6% of their life in automobiles.
In poorly ventilated dwellings, indoor smoke can be 100 times higher than acceptable levels for small particles. (WHO<< Household air pollutions and health>>2014).
Concentration of indoor air pollutant is higher than outdoor air concentrations on average, as 5~10 times globally (WHO<< Household air pollution and health>>2012), and 2 to 5 times in USA (1987. The total exposure assessment methodology (TEAM) study: summary and analysis. EPA/600/6-87/002a. Washington, DC ).

Not only for the air in buildings but also in vehicles or some other public spaces. Like the air in the NYC subway. Because of the density of people and poor ventilation, the airborne concentrations of three metals found in steel – iron, manganese, and chromium – are more than 100 times higher in the subway system than in aboveground air.( Airborne particulate metals in the New York City subway: A pilot study to assess the potential for health impacts. Environ Res. 2010 Jan; 110(1): 1–11.)
We have monitor for outdoor air quality, AirNow, EPA… to get these information. But how about the air quality in the environment just around us?

  • Problem target

So I started to think about how to measure air quality. The first thing is what is fresh air and what is polluted air.
So the bellowing are some definitions:

  1. Air quality: the state of the air around us. Good air quality refers to clean, clear, unpolluted air.
  2. Indoor air quality (IAQ): the air quality within and around buildings and structures. Dry clean air density.
  3. Clean Dry air: 12 gases that make up clean air are Nitrogen, Oxygen, Argon, Carbon dioxide, Neon, Helium, Methane (CH4), Krypton, Hydrogen, Xenon, Ozone(O3) and N2O. It should be made up with certain percentage of volume and weight. Nitrogen, Oxygen and Argon make up to 99.6% in total.

Then I think about what influence air quality. The 4 main factors that influence indoor air quality are Outdoor sources, Indoor sources, Amount of Ventilation, and Human factors. As I want to track the quality along you wherever you go, I focus on the first two factors.

Outdoor sources: Outdoor air pollutants that enter buildings through open doors, open windows, ventilation systems, and cracks in structures.
Indoor sources: Sources within buildings themselves.   Combustion sources in indoor settings, cleaning supplies, paints, insecticides, and other commonly used products that introduce many different chemicals, building materials. Other substances in indoor air are of natural origin, such as mold and pet dander.

The next step is to think about how to determine the polluted air with fresh air. So I took a look at the common containment components in the polluted air, and there are 2 main types:

  1. Contaminant Gas.
  • Radon
  • Carbon monoxide
  • Biological pollutants – Mites – Allergens – Moulds
  • Pesticides
• Ozone
• Asbestos fibers
  • Carbon dioxide
  1. Floating Particulate matter (PM). Also known as particle pollution, is a complex mixture of extremely small dust and soot particles. It is divided into two categories, “PM10” and “PM2.5.”  PM10 is matter less than 10 micrometers in diameter.  PM2.5 is even smaller – measuring 2.5 micrometers or less.


  • Air Quality Index

An air quality index (AQI) is a number used by government agencies to communicate to the public how polluted the air currently is or how polluted it is forecast to become.

Air Quality Index
(AQI) Values
Levels of Health Concern Colors
When the AQI is in this range: ..air quality conditions are: …as symbolized by this color:
0-50 Good Green
51-100 Moderate Yellow
101-150 Unhealthy for Sensitive Groups Orange
151 to 200 Unhealthy Red
201 to 300 Very Unhealthy Purple
301 to 500 Hazardous Maroon


The reported AQI is the calculated value for the past 24 hours in that area and, dependent upon each monitoring site.

USEPA uses the AQI for five major pollutants regulated by the Clean Air Act –
ground-level ozone,
particulate matter,
carbon monoxide,
sulfur dioxide
nitrogen dioxide.
For each of these pollutants, USEPA has established a scale based on the NAAQS to protect against harmful health effects.

EPA’s table of breakpoints

O3 (ppb) O3 (ppb) PM2.5 (µg/m3) PM10 (µg/m3) CO (ppm) SO2 (ppb) NO2 (ppb) AQI AQI
Clow – Chigh(avg) Clow – Chigh(avg) Clow– Chigh (avg) Clow – Chigh(avg) Clow – Chigh(avg) Clow – Chigh(avg) Clow – Chigh(avg) Ilow –Ihigh Category
0-59 (8-hr) 0.0-12.0 (24-hr) 0-54 (24-hr) 0.0-4.4 (8-hr) 0-35 (1-hr) 0-53 (1-hr) 0-50 Good
60-75 (8-hr) 12.1-35.4 (24-hr) 55-154 (24-hr) 4.5-9.4 (8-hr) 36-75 (1-hr) 54-100 (1-hr) 51-100 Moderate
76-95 (8-hr) 125-164 (1-hr) 35.5-55.4 (24-hr) 155-254 (24-hr) 9.5-12.4 (8-hr) 76-185 (1-hr) 101-360 (1-hr) 101-150 Unhealthy for Sensitive Groups
96-115 (8-hr) 165-204 (1-hr) 55.5-150.4 (24-hr) 255-354 (24-hr) 12.5-15.4 (8-hr) 186-304 (1-hr) 361-649 (1-hr) 151-200 Unhealthy
116-374 (8-hr) 205-404 (1-hr) 150.5-250.4 (24-hr) 355-424 (24-hr) 15.5-30.4 (8-hr) 305-604 (24-hr) 650-1249 (1-hr) 201-300 Very Unhealthy
405-504 (1-hr) 250.5-350.4 (24-hr) 425-504 (24-hr) 30.5-40.4 (8-hr) 605-804 (24-hr) 1250-1649 (1-hr) 301-400 Hazardous
505-604 (1-hr) 350.5-500.4 (24-hr) 505-604 (24-hr) 40.5-50.4 (8-hr) 805-1004 (24-hr) 1650-2049 (1-hr) 401-500 Hazardous

Revised Air Quality Standards For Particle Pollution And Updates To The Air Quality Index (AQI) (PDF). North Carolina: US EPA Office of Air Quality Planning and Standards. 2013.

Computing AQI:

  • Measure air quality

I tried 3 types of sensors up to now: MQ135, TP401, and MP503. I’m currently using TP401 as the prototype, but I will replace with MP503 later.

Name/Condition MQ135 TP401 MP503
Detection gas NH3,NOx, alcohol, Benzene, smoke, CO,CO2 ,etc. Secondhand smoke, CO,alcohol, volatiles of cosmetics, acetone, thinner, insecticide, correctin fluid, benzene, formaldehyde and so on. Volatile organic gas like Benzol, formaldehyde. CO. ammonia, alcoho. smoke dust and so on.
Material Nano- SnO2(Tin dioxide) doped with catalyst Nano- SnO2(Tin dioxide) doped with catalyst Not found
Graph of the sensitivity to gases Found Not found Found
Standard Detecting Condition(Vc: Circuit voltageVh: Heating voltage) Temp: 20±2Humidity: 65%±5%Vc: 5V±0.1Vh: 5V±0.1 Vc: 5V±0.1Vh: 5V Temp: 20±2Humidity: 65%±5%Vc: 5V±0.1Vh: 5V±0.1
Module Bought Sparkfun MQ135 air quality sensor Grove air quality sensor V1.0 Grove air quality sensor V1.3
  • Audience

Young white-collar girls who spend most of time indoors, love beauty, care about their health; people work in labs; at home.

  • Description

LeAirf is a wearable necklace air quality detector. It is able to detect temperature and many contaminating gases of low concentrations including CO, alcohol, volatiles of cosmetics, acetone etc. Then visualize the information by changing LED color and on mobile phone through Bluetooth. LeAirf is a combination of fashion & design, physical computing, circuit design, and mobile & server development.
LeAirf is the project after half-semester research of indoor air pollution. With the idea of quantifying self and monitoring health, it is targeted to provide the easiest way to detect air quality surround you.
LeAirf has two necklace box-shapes to hold the inside circuit module: seashell and leaf. Made with 3D Printing and laser cutting respectively. Both of them recall the connection of air and nature. The shape of box has the function of balancing ventilation that go through the necklace, which ensures reliable data read form the sensor.
LeAirf connects with mobile phone through Bluetooth Low Enegry. Main circuit components includes TP-401 air quality sensor (grove air quality sensor), RFduino micro controller and a RGB Led. We designed our own libraries so as to “fake pair” with mobile app through BLE as well as calibrate & adjust sensor data.
The mobile app is made with PhoneGap. It connects the server which is written in nodejs and data stored in MongoDB.

  • Summary
      • Air Detection: Quantify your surrounding air environment (Air quality and temperature). Bring the consciousness of air quality and air pollution.
      • Wearable: Personal use. Quantified well-being. Solve the problem of the lack of IAQ information, measures air quality on the spot, wherever you are.
      • Communication: Bluetooth link to your phone.
      • Notification:

Private : Visualization of synced data on mobile phones; Line graph of past AQ data;
Public: LED index of air quality.

      • Intervene: Share information in small community.
      • Shape: Fashion, design. Remind you of the old good time. Fine wood.
      • User: Young white-collar girls who spend most of time indoors, love beauty, care about their    health; people work in labs like ITP; at home.
      • Use places: Home(especially new houses); Vehicles; Large buildings; Labs.
      • Scope of intimacy : As private as your personal accessory; As public as a public indoor air quality sharing device.
      • Technical solution
Sensor Communication Web Mobile
TP-401 Gas SensorSemi-conductor RFduino Hybird App
SnO2(Tin dioxide)Resistance decrease in fresh clean air.They are used in air quality control equipments for buildings/offices, are suitable for detecting of NH3,NOx, SOx, ,etc.Cost efficient. Arduino+ Bluetooth + Temperature sensor Nodejs + MongoDB to store data PhoneGapBluetooth sync transfer data
      • Use cases

      • Work process

      • Trouble shooting

The biggest problem I met is the sensor. The number read from the sensor is actually super wired. It did not change too much in different conditions with MQ135. And there is no library for the sensor. The document said that it needs adjustment. It is recommend to calibrate the detector for 100ppm NH3 or 50ppm Alcohol concentration in air and use value of Load resistance that (RL) about 20 KΩ(10KΩ to 47 KΩ). This is actually impossible for me to make the environment with 100ppm NH3 or 50ppm Alcohol concentration.

So I moved to TP401, things became much better when more resources are available. However, I found the library has too many bugs. Doing twice the same average things and so on. I wanted to figure out what the number means or is it possible to map the value to the AQI or gas concentration. So I need a graph. However similar graphs like sensitivity graph is missing from the document.

Then I asked Tom Igoe(so excited because it was the first I talked to him). And he was so patient to help me figure out the TP401 sensor library/document, and some other problems. Although the conclusion is that it might be impossible for me to adjust the sensor value, I understand the mechanism much better than before.

He also offered a good suggestion about building an air house to let stable ventilation go though the sensor container. Which is very helpful.

      • Current process


Codes: https://github.com/streamna/networkprojects/tree/master/Leairf




One thought on “[Wearable] LeAirf – Air Quality Detection Necklace

  1. marina

    Great work, Stream! It’s good to see you connect it to your personal motivations too. I’d still like to hear you assess the take-aways and next steps outlined in the post-mortem on the assignments page. But that’s mostly for your own practice, not for my needs.