Singapore haze



On June 19th, Singapore Pollution Index (PSI) rose to 321. This is the worst air pollution crisis in Singapore’s history. Illegal burning of forest to clear land for palm oil is a recurrent problem in Indonesia and Singaporeans are somewhat used to haze this time of the year. But this time is the worst ever and commercial pressure against companies causing the haze could come too late.

This level is recognised as hazardous. Below are some advice for my friends in Singapore:

  1. Stay indoors : keep doors and windows closed. If you have an air-conditioner, use the air filtration mode.
  2. If you need to go outside, use a mask to cover both your nose and mouth. It should catch tiny particles below 0.3 microns.
  3. if you are driving, windows should be rolled up, use your car air-filtration system if you have one.
  4. Avoid any physical effort if you are outside. Indeed, the air volume you are inhaling can be 25x higher if you are running compared to walking.

MIT start-up Infipure develops invisible nose air mask

Pollution masks are pretty common in China, particularly during pollution peaks. But a new solution has been developed by a team of MIT grads. The idea of the Infipure ‘invisible mask’ comes from a simple observation about the human body; most of the time people breathe in through their nose (except during physical activities or a cold).The design is pretty interesting as it looks much better than regular masks. Small filters are  inserted directly into the nose. The patented ‘NoPM’ filter technology filters out up to 99 percent of PM2.5 air pollution particles.


© Infipure invisible mask’s design

Infipure has been selling the invisible air mask on Taobao for two weeks. They offer three sizes and are pretty cheap. 


© infipure product

There is not a lot of technical detail available yet. So it is not clear how effective the masks are. How often the user should change the mask is also unclear. But it is worth trying. The air cleaner and air mask markets are booming because the general public in China is now very concerned about air pollution. I am overall pretty enthusiastic about the idea of Infipure. The start-up is offering a short term solution to a public health emergency. And I am also glad Infipure’s founders are co-MIT grads!


© Infipure invisible mask

Monitoring Indoor Air

People living in urban areas spend more than 80% of their time indoors. This number is even higher for sensitive populations, such as children and the elderly. So it is not surprising to see projects emerging in the field of  indoor air quality monitoring. Some projects have an impressive design of both hardware and mobile app, however the air quality part is often limited to CO2. Anyone serious about indoor air pollutant tracking should also integrate other critical indoor gas pollutant monitoring, such as VOCs.

Netatmo has developed a sleek personal weather station, with the vision of creating a weather and air quality monitoring network. The parameters measured include indoor temperature, CO2 concentration, noise, and humidity. Useful applications include indicating the best time to ventilate, recommendations for outdoor activities or pollution peak alerts on your mobile phone. However, it is not sure whether people would be interested in sharing this data on social networks. The station is currently sold for around 170 Euros.


© Netatmo

CubeSensors are two-inch cube shaped devices tracking temperature, air quality, barometric pressure, humidity, noise, vibrations and light, with wireless capabilities. Data are analyzed and recommendations to improve the indoor conditions are delivered via a mobile app. No available information on the type of air pollutants are available yet.


© CubeSensors

Sensors; making the invisible visible

The explosion of Internet-connected sensors has created low-cost granular monitoring capabilities. Some exciting projects of connected sensors tracking outdoor air pollution have emerged in the last few months:

Air Quality Egg is a community-led air quality sensing network. The Egg is allowing anyone to collect high resolution readings of nitrogen dioxide and carbon monoxide concentrations with low-cost DIY sensors. This project has a strong focus on a crowd-sourced approach and is a good example of collaborative open source technology projects emerging in the air quality area.


© Air Quality Egg

AirBot is a pocket-sized particle counting sensor developed by Carnegie Mellon University. Their vision includes community-generated maps and data visualization. The project is still in a prototype phase but the lab plans to market AirBot next year (around $99). Technical information will soon be available.



Intel has also recently developed sensors located closer to where air quality really matters, i.e. where people are breathing. The project is in pilot phase and will be implemented first in Dublin, Ireland. Sensors will track oxygen, nitrogen, carbon dioxide, and carbon monoxide but not PM.

Sensaris is collecting environmental data such as noise, carbon dioxide  carbon monoxide  fine particles, humidity, temperature, along with positioning information via a portable sensor (Senspods). Data are sent wirelessly to mobile phones.  The project aims to engage citizens to collect data and share them via social networking applications in order to map air quality in cities.

Sensordrone is a Kickstarter project of a sensor monitoring gasses, temperatures, humidity, alcohol breath, gas leak, light, etc. They also developed a mobile app with some functions but call for new ones to be developed by users with open source software. Sensordrone  is aiming at expanding public air quality monitoring stations network and get more relevant information (air quality where people actually live). This sensor project could lead to many exciting projects. For air quality monitoring, 3 sensors are included:

  • Electrochemical Gas Sensor: calibrated for Carbon Monoxide (can also be used for precision measurements of Alcohol, Hydrogen, and others)
  • Gas Sensor for Oxidizing Gases : MOS (Metal oxide semiconductor) type for Chlorine, Ozone, Nitrogen Dioxide, etc.
  • Gas Sensor for Reducing Gases – MOS type for methane, Propane, alcohols, other hydrocarbons, etc.


© Sensordrone

© Sensordrone

AirWaves is a pollution mask equipped with particle sensors and a wireless connection, sharing data via a smartphone app. Users are  contributing to map air quality and adapt their behaviour to real-time pollution (by avoiding highly polluted areas for example). The mask is one of eight winning wearable technology concepts spawned by an internal competition at Frog Design and was designed by a team from Shanghai. Visually shocking, it is using the same idea of many other wireless air quality sensors; building an air quality map of the city via crowd-sourced data monitoring.

Frog Design

© Frog Design

Mobile app; your air in your phone

Air quality monitoring mobile applications have surged in China after the recent episodes of pollution peaks. Overall, this is only a start and the apps currently available lack reliability or real-time recommendations functions. Some examples are listed below. If you want more information, you can visit the blog Beijing tech report.

  • Air Quality China displays an average air quality index for about 140 Chinese cities. A simple color code is used to inform users about hazardous air conditions (included PM2.5 and PM10, when available).

© Air Quality China

China Air Quality  aggregates data from more than 120 cities , ranking them according to a “pollution index” . The app uses data from both the US Embassy and China’s Ministry of Environmental Protection (PM2.5, PM10 , SO2, NO2).


© China Air Quality

In other locations, several apps and projects are also available.

  • AIRNow, developed by the US EPA, offers forecast and real-time monitoring of PM2.5 and ozone, as well as interesting visuals and health recommendations.
  • Breath! is a mobile application providing near real-time air quality data for a wide range of locations and regions which will be released in few months by prodevelop (spanish R&D company). Breath! will use air quality data provided by GMES (Global Monitoring for Environment and Security by European Space agency). It will also use data from local authorities or crowd-sourced. Other parameters, such as weather, wind, waves, water quality and UV index will also be available to offer advices for users performing outdoor activities.


    © Breath! predevelop


Should you buy an air Cleaner?

The first rule to improve your indoor air quality is to ventilate in order to recycle the fresh air. But what if the outdoor air is really bad? Or the climate extreme ? If you live in cold Norway, hot and humid Singapore or foggy Beijing, you may be considering to buy an air cleaner (also called air purifier). In Asia, air cleaners are becoming a common home appliance that people buy, like they would buy vacuum cleaners. Many technical words are used to describe working processes of air cleaners: electrostatic precipitators, HEPA filters, ionizers, sorbents, plasma, UVPCO, etc.

This post is aimed at helping you to see clearer and understanding the basic principles of these different technologies, as well as their potential risks. Be aware that there is no proper certification for air cleaners. So consumers are left with no choice but to believe the claims of air cleaner manufacturers. Indoor air pollution is not visible, which make it easy for companies to claim efficiency, even when the device provides no significant improvement. Finally, there is no requirement to test side-effects, such as ozone emissions. So consumers need to check the technical parameters to ensure a safety.

Most air cleaners combine different technologies. There are three major technologies commonly used to remove particles:

  1. Mechanical filters
  2. Electrostatic precipitators
  3. Ionizers

and three main technologies targeting gas pollutants

  1. UVPCO
  2. Sorbent
  3. Plasma System

I will  describe technologies in 2 different posts: Removing gas pollutants; let’s talk Tech!  and Removing PM: let’s talk Tech!

A good start to get a basic understanding of air cleaning technologies is the EPA summary on Residential Air Cleaners.

Removing PM; let’s talk Tech!

Air cleaners use different technologies to remove particles. What is the difference between mechanical and electrostatic filters? Are ionizers safe?

Mechanical filters 

How does it work?

Nothing very complicated or new in the basic technology of mechanical filters; particles are captured by fibrous media. But mechanical filers can also remove other types of pollutants: airborne viruses, bacteria, mould spores, allergens or gaseous pollutants, adsorbed by accumulated particles on the filter surface. There are different sizes and thicknesses of media filters using various materials and performing at various efficiencies (open-cell foams, non-woven textile cloths, paper-like mats of glass or cellulose fibres, wood fill, animal hair or synthetic fibres). High efficiency particulate air filters (often called HEPA filters) can remove 99.97% of PM of diameter below 0.3microns. Filters suffer from pressure drops and require relatively high energy compared to other alternatives.

Are there potential side effects?

Some portable air cleaners (not integrated to air handling units) with mechanical filters are pretty noisy (comparable to the noise of a washing machine, i.e. 50 to 75 dB). If equilibrium conditions are disturbed (change of airflow, temperature or relative humidity), there is a risk of desorption and release of pollutants. Gaseous pollutants may also be transformed into other pollutants. The loaded filter surface may also create a natural sink for ozone, often reacting with pollutants accumulated on the filter surface. So proper operation and maintenance of air filters is essential to make sure beneficial effects are greater than side effects. Code of practice uses 6 months or a year before changing a filter. However there is generally no way for users to know when to change the filter, as it depends of the pollution level and could be different from the lab conditions.

Electrostatic precipitator (ESP) 

How does it work?

This technology is less common than filters but is integrated in some portable air cleaners. One clear advantage of this technology is the low pressure drop  compared to mechanical filters. Thus ESP are less noisy and more energy efficient. When an ESP is operating, high voltage is applied to an air stream, providing electric charges to particles. The charged particles are then attracted to plates (or filters) of an opposite electric charge. Airborne bacteria, mould spores and allergen are also removed by a rafting process. But as PM accumulate on the plates surface, electric attraction decreases, so the Electrostatic precipitator requires regular cleaning.

Are there potential side effects?

Ozone is generated by the high voltage. Ozone is harmful by itself and can also react with other organic compounds to form harmful by-products such as formaldehyde. Ozone generation is currently not well documented because there is no legal requirement for manufacturers so if you choose to use this technology, you should choose lower voltages or systems with carbon filters (to remove VOCs).


How does it work?

Ionizers (also called ion generators) send bipolar ions into the room. The PM then becomes charged through direct contact with the ions. Charged PM accumulates and attaches to surfaces (walls, tables, floor, etc.). Ion generators may also cause charged PM to carry airborne biological pollutants. Experts have been expressing doubts on the ability of ionizers to work efficiently. Indeed, the volume of air treated may be too small, limited to the direct vicinity of the device.

Are there potential side effects?

Ionizers are generating ozone, which is harmful in itself (increasing the risk of respiratory diseases) and may also react with other organic compounds to form harmful by-products such as formaldehyde.