Tarquin Investigates: The Case of The Missing PM2.5

I bought an electronic air quality monitor last summer and since then I’ve been monitoring the pollution levels inside our apartment – and crucially in our kids’ bedroom. Before I got the monitor everything was guess work: I couldn’t tell how effective the filters were, whether they needed replacing, which size to purchase, etc. 

The good news its that the Sharp air filters we’ve been using (and are readily available in India) are excellent. That said, if we kept the doors and windows open, there wouldn’t be any point in having them. I’ve found that the levels inside our apartment in south Delhi aren’t much lower than those outside. In other words, remaining inside and breathing unfiltered air doesn’t make a whole lot of difference when Delhi’s air quality is unhealthy to hazardous i.e. for the entire winter.

So here’s what I recommend, based on my own little controlled experiments. Adopt some simple – albeit tedious – practices and you can have good air quality inside the house round-the-clock – that is assuming you don’t live in a mansion, in which case you might want to think again.
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1. Contact one of the indoor air quality monitoring companies and get a rep to come and estimate how many machines you need. HEPA filters capable of trapping PM 2.5 are essential.
2. Before the machines are switched on, seal all windows or at least close them as tight as possible – ditto gaps beneath doors, especially those opening to the outside.
3. Keep doors inside closed as much as possible to create air pockets. Our sitting room, kitchen and the kids’ playroom is essentially one large area and I manage to keep the levels at an acceptable level throughout the day. Ditto my office, which is small and therefore easy to filter. At night it’s not such a challenge, either. But again, bedroom doors must remain closed. 
   
4. Once the doors are closed, the Sharp machines working at full blast take around one hour to clean the air to a desirable level (at which point a lot of the same, clean air is being circulated over and over again). To maintain a good level throughout the morning when the pollution is at its most intense, I have to keep the filters set at maximum. This is a little noisy, but to us, worth it. After lunch, the machines are generally turned down to medium.
5. I turn the machines off in our living area and office at night, but they go back on at around 6 PM. I turn the bedroom ones on at around 6 PM.
6. Clean the filters once a week. I vacuum the pre-filters and lightly brush the crenulated HEPA filters.
7. Change the HEPA filters every three months without fail.

Please also note the following:

• Some companies supply extra pre-filters for the largest two Sharp models. These are a must for trapping the largest particular matter and help prolong the life of the hepa filters. The pre-filters can be vacuumed and washed. When the levels are as apocalyptic as they’ve been recently, ours get coated in a thick layer of crap in a matter of days.
• Cooking on gas releases lots of PM2.5, which is extra work for the filters, so worth closing the kitchen door when cooking and turning on the extractor fan, if possible.
  
• ​Buy an air quality monitor. Mine cost $200 and is manufactured by Dylos in the USA dylosproducts.com. It’s simple to use - provides instant data for PM 2.5 and PM 10. 
  
• As a general guide to how many machines are required: we have a three-bed apartment with a playroom. The machines cost about a lakh (100,000 rupees). But I move them around a bit – for example, I take the one from the kids’ bedroom and use it in my office during the day.
  

NB When the levels are as consistently high as they've been over the last few months, the filters need changing every two months. It's worth noting that the full compliment of filters in my house i.e. six Sharp machines, costs 25,000 rupees.

​Tarquin Hall​
Tarquin Hall is an English journalist, blogger and novelist. He is the author of the Vish Puri series and lives in New Delhi with his wife, BBC journalist Anu Anand and two young children. He has been investigating how best to fight air pollution in New Delhi.