This article provides the testing method and data for the article Delhi’s Indoor Air Pollution Lower than Outdoors.
1. Test Method
I collected data January 12th to January 29th, 2019. I collected data at each place once to avoid over-representing a single place in the data. These days were quite polluted, with PM2.5 averaging 275.8 micrograms per meter cubed. The lowest outdoor reading was 191 micrograms. The highest was 417 micrograms.
I tested air directly outside the entrance of each building, allowing 30-60 seconds for the AirVisual to give an adequately stable reading. The fact that I ran the tests in January could be relevant because rooms may be better sealed in the winter than in the summer. Because Delhi is fairly cold in January, people are more likely to close windows and doors.
The locations I tested were diverse, from a large international hotel to a regular apartment. Although there is a wide range, these places tend to be in wealthier parts of Delhi, such as Saket. If one theorizes that wealthier places tend to have better air or better-sealed rooms, then the indoor-outdoor percentage may be higher in less-well-off parts of town.
I did not test in any place that kept windows or doors open constantly. I also avoided places that were using purifiers or central air systems with filters (that I knew of). However, one exception is that the manager of the Sheraton hotel told me that the air in the lobby is filtered. At the same time, the lobby doors are opened frequently. The average in the lobby (61%) was fairly close to the overall average (68%). Thus, removing this datapoint would have minimal effect on the overall results.
3. Time of Day
The original data includes dates and times of day. Timings ranged from 8:40AM to 8:44PM, covering diverse parts of the day.
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