How Many PM_2.5 Sensors are Needed to Estimate Daily and Annual Deployed-Network Mean Concentrations in City-Scale Sensor Networks?

We examined how well smaller subnetworks reproduce deployed-network daily and annual or study-period mean concentrations using data from Dhaka, Bangladesh (<i>N</i> = 35; annual mean 55.15 μg/m³), Lucknow, India (<i>N</i> = 71; annual mean 61.80 μg/m³), and the nine-month Open Air Chicago network (<i>N</i> = 277; period mean 10.24 μg/m³).

For each subnetwork size <i>n</i> ≥ 2, mean estimates from 10,000 simple-random-without-replacement draws were compared with the corresponding deployed-network mean; the <i>n</i> = 1 errors were enumerated exactly. At <i>n</i> = 10, the period median absolute percentage error (MdAPE) was 3.9%, 5.6%, and 1.9% in Dhaka, Lucknow, and Chicago, respectively, and the across-day median daily MdAPE ranged from 2.6% to 5.8%. For a single sensor, the period MdAPE ranged from 5.2% to 17.8%, whereas the corresponding 95th-percentile absolute percentage error (APE) ranged from 18.5% to 59.9%, demonstrating that typical and tail performance must be considered together.