Fine particle dust is hard to filter from air, because filters with a mesh size of a few microns don’t let enough air through to be practical, unless you invest a lot of energy to push it through. Now researchers in Hong Kong have developed a new type of nano filter that does allow a person to breath through it, but also catches the smallest (and most dangerous) praticles.
“The multi-layer nanofibre mask can block out at least 80% of suspended nano-aerosols, even the ones smaller than 0.3 micrometer. In the meantime, the wearer can breathe as comfortably as wearing a conventional face mask, making it superb for any outdoor occasions. Another option is to provide a nanofiber mask that has the same capture efficiency as conventional face mask, yet it is at least several times more breathable, which would be suitable for the working group.” (source)
Fine particles are dangerous because instead of getting stuck in the lungs, they enter the blood stream and circulate around the body, accumulating in the heart and brain. Diesel fumes have for this reason been associated with higher heart failure risk.
“Edinburgh University scientists found minuscule particles produced by burning diesel can increase the chance of blood clots forming in arteries.” (source)
In mice it was shown that early exposure to diesel fumes can cause problems later in life, whereas people raised in clean air have less problems. A face mask air filter that can prevent exposure to these particles is a great step, and no doubt welcome in heavily polluted China.
Smog in Bejing
The filters can also be used to neutralize NOx and other emissions, probably by combining them with carbon filters or neutralizing chemicals. This can be a great benefit for urban areas where it can help remove smog where it is concentrated, for instance at the exit of tunnels.
A very effective way to remove fine particles is the electrostatic precipitator. It charges fine particles and then applies an electric field to separate them from the airflow. This however requires quite a lot of energy. Combining the electrostatic effect with water mist (to capture particles) has shown to be very effective (link follows), but this is water hungry. A method that only needs forced ventilaton seems to be superior, especially when it can be powered with renewable energy.
An interesting aspect is that a filter that catches micron scale particles can also desalinate water. The pores of a Reverse Osmosis filter lie in the range of 0.1 to 5,000 nm (4×10−9 to 2×10−4 in), so the minimum is 100 microns (or micrometer). There’s a difference between water and air of course, but maybe the same technology can bring us large surface low pressure and lower cost RO desalination.