Advances in particle sensor design and manufacturing have enabled the development of low-cost air quality monitors (LCMs). The sensors use light scattering to estimate mass concentration and thus require evaluation for aerosols of varied composition and size distribution. We tested the performance of six LCMs designed for home use and having a retail price under US$300 in October 2018. We assessed their performance by comparing their output to reference PM2.5 and PM10 measurements from 21 common residential sources and from infiltrated outdoor PM2.5. Reference data were obtained by using gravimetric measurements to adjust time-resolved output from an aerosol spectrometer with both electrical mobility and optical particle sensors. Compared by linear regression to reference measurements, LCMs had negative intercepts and slopes of 1-2
for infiltrated outdoor PM2.5. Semi-quantitative responses (~50–200% of actual PM2.5) were obtained for varied aerosols including minerals (ultrasonic humidifier, vacuuming, test dust); combustion products (incense, mosquito coil, extinguished candles); microwave popcorn; and cooking involving frying or grilling. LCMs had low or no response to sources for which all mass was in particles smaller than 0.25 (micron)m, including steady candle flames and cooking without frying or grilling. PM10 data from LCMs was more variable than PM2.5.