Underground air pollution can be 20 times higher than roadside air. Inspired by how Nature uses rain to clean air, Airtomo releases dry, atomised water vapour to deposit and remove Particulate Matter (PM) 2.5 and 10 through a process called aggregation.
Our battle with air pollution is not just above the ground, it is also under. According to the Financial Times in 2019, pollution on the London Underground can be 20 times higher than roadside air. PM 2.5 and 10 are tiny particles that can enter our lungs to cause damage – damage equivalent to smoking a cigarette if you spend just 20 minutes underground. As a commuter who struggled with asthma, this article resonated strongly with me. I was inspired by Nature and how She uses rain scavenging to trap and remove particles in the air. To emulate this phenomenon, water atomisation technology is used to create vapour clouds that clean polluted air.
Atomisation is the process of breaking up bulk liquids into droplets. At the heart of the technology is an ultrasonic transducer disc. It vibrates at a high frequency (kHz) and transfers that mechanical energy to the body of water in contact. As water exits the atomising surface, it is broken into fine vapour of uniform droplets between 9 and 20μm. At that size, the water droplets are dry to the touch. Yet, they effectively remove PM from the air as the droplets envelop PM 2.5 and 10 to form large, heavy aggregates which fall to the ground.
They no longer resuspend, even after water has evaporated, and can be easily removed with a mop or broom. Airtomo wearables offer a vapour cloud to clean the air one breathes or prevent PM from resuspending into the air. Airtomo can also be adopted as an infrastructure system. Scout modules’ infrared sensors detect train or human motion (which increase PM concentration) and inform the main unit to release vapour via Wi-Fi.
Interestingly, the project began with adhesives. Much like how lint rollers collect clothing fibre, small containers were fitted with vinyl stickers to trap PM. There were tested inside a sealed chamber and on a bobbing mechanical foot that imitates human motion. The results were captured by an air quality sensor. While unsuccessful, the tests inspired the usage of pneumatics, e.g. vacuum cleaners, to improve trap rate. They performed better but air filters saturate easily and require replacements. That hassle prompted the usage of electrostatics and ionisers to capture and deposit PM. Both were effective but needed electrical grounding to function.
The search for an alternative solution landed on liquid filters. Instead of an air filter, a body of water efficiently entraps PM. Hence, further research was conducted on water as a medium, e.g. in bubbles, and eventually rain and how Nature uses it to clean air. To mimic rain, water was misted from a spray bottle and PM concentrations dropped significantly. That questioned if reducing droplet size is key to removing PM. A water atomiser was thus used to validate the hypothesis and it was proven to be true. Subsequent tests tinkered with various vibration frequencies to obtain different droplet sizes by changing circuit resistance.
Water atomisation is not novel. The application of this technology to remove PM and air pollutants is. In fact, water atomisers come in a familiar form – humidifiers. The main difference between Airtomo and other water atomisers lies in the droplet size, which can be determined by the transducer’s vibration frequency. Most products operate in the MHz range while Airtomo operates within a specific, low kHz range. In addition, electrostatic-charged vapour, which is employed in Airtomo infrastructure modules, exhibits enhanced particle suppression qualities and this technology is unique to the field of air purification. A single Airtomo atomiser cleans 167l of air in a minute with a 40cm effective cleaning range. This is 1.5 times more than the total air exchanged by an average adult, which is 110l every minute. Airtomo also consumes nominal resources. It requires 1.5W of power to operate and a single atomiser consumes only 23ml of water in an hour.
All the experiments thus far were tested in a sealed chamber (the largest being a 3.3m3 space) to ascertain the effectiveness of atomised water vapour in removing PM from the air. With that said, the performance is likely to be affected by other variables such as wind speed, direction, and humidity. Hence further studies would need to factor in these elements and should be conducted in a larger, open space to achieve a holistic analysis. Given the success of the lab tests, I hope to promote Airtomo as a decentralised, air purification system where individuals and the infrastructure can collectively improve the environment’s air quality.
All images with courtesy of Kevin Chiam