This is PART II of a two-part series. Check out the first part here.
As the air worsens for the winter, you may find yourself wanting to protect your family with air purifiers, masks, or a pollution sensor, but are uncertain how to select and use them. Here are some tips on to get the best:
Air purifiers:
HEPA filters are essential to remove PM2.5. Jeff Smith, a founding member of Help Delhi Breathe, advises looking for models with HEPA filters rated H13 or H14.
Many purifiers use carbon to remove odours and some harmful gases. Smith recommends those models that feature several kilos of activated carbon (or alumina).
Some models also feature ionisation technology. Barun Aggarwal, CEO of Breathe Easy, told us that ionisation is not essential (and can be harmful), so look for an air purifier with an option to shut this feature off, in models that use it.
A larger number of filters does not necessarily equal better performance.
Look for a unit that is portable. So it can be used in the bedroom at night, and in the living room in the day.
Smith cautions against machines that take air in only at the floor level as the filters will quickly get clogged with dust and larger particles.
To determine the required number of purifiers, Aggarwal suggests halving the square footage recommended by the manufacturer, as their numbers are based on ideal conditions and with the machine operating at high speed, which is often quite noisy.
Clean air delivery rate (CADR) is a metric used by manufacturers. A high CADR is important as buildings in India let in a lot of unfiltered, outside air. Therefore, a purifier that cleans the air well but cannot circulate the air in a room through its filter fast enough will not be effective.
Doors and windows must be kept closed for the purifiers to be effective. Open windows once a day for about an hour to reduce CO2 levels.
Purifier filter maintenance:
Vacuum or wash pre-filters, but never wash a HEPA filter and avoid vacuuming HEPA filters as they are easily damaged.
Check HEPA filters regularly and replace as per the manufacturer's instructions (up to 2 times per year in the most polluted places).
There are many products on the market, but a few that have been independently tested for the efficacy of their filters without any emission of harmful gases and their CADR include Sharp and IQAir.
Car purifiers are now available, but may not be necessary if your car has high-quality filters. Aggarwal advises people to test their cars before investing in one.
Masks:
Effective, inexpensive masks should be rated N95 or higher, such as Venus, 3M, and Honeywell masks. These masks cannot be gotten wet, are available only in adult sizes, and are disposable. When the mask is visibly soiled (or, in the case of a green, carbon-containing mask, when the smell of the filtered air changes), it must be replaced.
Masks are available in different levels of resistance. Lower resistance masks are not as effective at filtering particles, but are easier to wear during aerobic activities, and have one-way exhalation vents.
The more expensive masks, such as Vogmask and Cambridge mask, come in sizes for children. Aggarwal cautions that they can be very carefully surface cleaned, preferably after removing the valve, but not soaked nor wrung out to dry. Each manufacturer provides guidelines, but in unhealthy (red on AQI scale, PM2.5 56-150 µg/m3) conditions, one Cambridge mask can be worn for approximately 220 hours.
A mask is only effective when it fits snugly, with a metal piece across the nose and tightened at the base of the chin, as per the manufacturer's instructions.
Extend mask life by storing in a ziplock bag when not in use.
Do not wear masks for long periods of time as it can lead to higher exposure to CO2 (pay attention to symptoms: dizziness, headache, fatigue).
Nasal filters offer an exciting new type of protection against particulate pollution. They are more discreet and comfortable than masks. The self-adherent films that cover the entire nostril (versus alternatives that must be inserted into the nose) are the most effective.
Air pollution sensors:
Check online real-time resources for monitoring stations near you (e.g. http://clonewdelhi.com/custom/AQI/missionindiaaqi.php#, and http://aqicn.org/city/delhi/ito/, https://openaq.org/#/?_k=pt2rau).
Sensors can be purchased that measure a combination of PM2.5, PM10, carbon dioxide (CO2), and total volatile organic compounds.
Sensors come in three categories: A, B, and C grade sensors. The most readily available are C-grade sensors, which are good enough to tell the relative difference in air quality with or without an air purifier on (or indoor versus outdoor). However, readings from these sensors can be variable. More reliable and expensive are A- or B-grade sensors, which are reference grade (EPA approved) or commercial quality, respectively.
Aggarwal suggests using sensors only for the length of time required to make a measurement, then shutting them off and keeping them inside to prolong the life of the sensor, which may need to be replaced every 18 months to 2 years. Ideally, look for a model that allows for the replacement of the sensor after this period. Occasionally compare measurements with the closest publicly-available monitoring stations to make sure the sensor is still functioning well.
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