Introduction Independent workers often work in Taiwan’s coffee shops. However, there is not enough information for workers to notice poor indoor air quality (IAQ), such as high concentration of particulate matters (PMs) and carbon dioxide (CO2).

Objectives This study aims to explore indicators of IAQ for independent workers in the coffee shop industry.

Methods Investigators as mystery shoppers went to several coffee shops in metropolitan area of Taipei and New Taipei City to measure indoor conditions and IAQ. Every selected shop was surveyed twice; each measurement lasted 3 hours. Size-fractionated PMs including PM10, PM2.5, and PM1 as well as CO2 were measured by miniature parity monitoring instrument (AS-LUNG) every 15 seconds. Indoor conditions including temperature, and relative humidity (RH) were also measured by AS-LUNG every 15 seconds. Moreover, investigators recorded the weather, condition of indoor ventilation, occupant density, presence of tobacco odors, and customers activities as indoor conditions every 10 minutes. Random forest models R(4.0.3) were used to explore the impact of indoor conditions on concentrations of indoor size-fractionated PMs and CO2.

Preliminary Results The average indoor concentrations of PM10, PM2.5, and PM1 and CO2 in selected coffee shops were 9.75 μg/m3, 8.49 μg/m3, 6.18 μg/m3 and 1079.46 ppm, respectively. Indoor air flow and temperature conditions were two major indicators of IAQ. When opening the window or when the temperature is higher than 20.5°C, concentration of PMs and CO2 increased.

Conclusion Independent workers could use the shop’s indoor air flow and temperature as simple indicators for workplace IAQ. Using the results of this study, workers will be able to select working place with suitable IAQ.