New Delhi: Even before Diwali celebrations kick off in Delhi, air pollution levels have reached hazardous levels. On Monday, the PM2.5 (pollutants that are smaller than 2.5 microns in size) level in the national capital region reached 644, more than 10-times the safe level set by the Indian government. The Centre’s System of Air Quality and Weather Forecasting And Research (SAFAR) recorded the city’s air quality index (AQI) as “severe”, the worst grade possible.
Masks that reduce the risks associated with inhaling pollutants have now become an important accessory to residents of the city. However, not every mask is helpful or efficient. Research has already shown that simple surgical or cloth masks are ineffective when it comes to protection from finer particles such as PM2.5. Instead, experts have recommended a class of masks called N95 and N99 respirators because they filter out smaller pollutants as well.
These respirators (or masks) are subjected to rigorous testing. The term N95 denotes that the respirator blocks out at least 95% of very small particles (less than 0.3 microns). N99 respirators block out 99% of these particles. These marks are closely fitted to the mouth and nose, as opposed to simple surgical masks, which are fit loosely. This is crucial, and even slight variations may impact their efficiency. Manufacturers have warned that N95 and N99 masks may not be as efficient as promised if the user has facial hair.
How do N95 and N99 masks work?
Most modern masks made of fine fibres and which filter out pollutants employ three mechanisms to filter harmful particles out: inertial impaction, interception and diffusion.
Inertial impaction helps to filter out particles that have too much inertia due to their larger size or mass. A filter fibre helps divert them around the airstream, preventing their inhalation. The interception mechanism is also used to filter larger particles. As the name suggests, the fibre intercepts the particle and prevents it from entering the airstream. Diffusion helps filter out smaller particles that are constantly bombarded by air molecules. When they come into contact with the fibre, they are deviated from the airstream through diffusion.
Some advanced masks also have a fourth mechanism – electrostatic attraction mechanism – which utilises oppositely charged particles to collect pollutants located on a charged fibre.
All four mechanisms function on the same premise: the filter fibre has strong molecular attractive forces that hold on to the pollutant particle, preventing them from entering the airstream.
It is difficult to remove the particles from the filter once they have been collected. Therefore, the efficiency of the masks reduces after extensive use, and there is no fixed period after which the masks become ineffective. Some masks also come with replaceable filters.
Doubts over the efficiency of N95 masks
A study published in April this year tested the performance of nine masks, including at least five of the N95 grade that claimed to protect users from PM2.5 particles. It found that although the masks may filter tiny particles as advertised, factors like face size and shape in addition to movement could lead to a leakage as high as 68%.
The researchers told Reuters that even if the mask fits the person at first, it “may not continue to give a good fit as the person goes about their daily activities – walking, talking and more”. When the masks were tested on volunteers who were performing sedentary tasks (such as sitting) and active tasks (such as standing and walking), the leakages were found to be significant. During sedentary tasks, the average leakage around mask edges ranged between 3% and 68%, while it was between 7% and 66% during active tasks.
N95 and N99 masks in India
Every November, reports suggest that the sale of anti-air pollution masks and air filters in Delhi has spiked. The combination of high vehicular density, crop stubble burning in neighbouring states such as Punjab and Haryana, dropping temperatures and bursting of firecrackers for Diwali make the air quality in the city hazardous.
Nirvana Being, a popular destination for purchasing masks and air purifiers in Delhi, said that it had already sold 500% more anti-air pollution masks this October when compared to 2017. The market for air purifiers and anti-pollution mask is estimated to be growing by 30% every year. In this scenario, several players have also entered the market.
The prices for N95 masks range from as low as Rs 60 (3M 9010) to Rs 3,600 (Dettol SiTi Shield). The cheapest N99 mask costs Rs 205 (3M 9332), while the most expensive will make your wallet lighter by Rs 5,300 (Atlanta Healthcare Cambridge). The 3M masks are cheaper because they do not come with disposable filters and must be discarded after a few uses. The more expensive masks come with disposable filters or filters that can be cleaned.