Response of low-cost sensors to high PM2.5 concentrations during bushfire and haze events

Low-cost sensors are becoming an important component of air quality monitoring. They are used in various outdoor areas beyond the protective enclosure of air quality monitoring stations. Therefore, they are exposed to a wide range of environmental conditions. In this study, we investigated the operation status and performance of an air quality monitor consisting of low-cost sensors for measuring PM2.5 and CO under extreme air pollutant concentrations. Over deployment periods of three haze episodes in Beijing, China, and two bushfire episodes in the Blue Mountains, Australia, the monitors collected air quality data for community and research users. During the extreme air pollution episodes, the operation of the monitors was not affected by the extremely high PM2.5 and CO concentrations. They showed the greatest overestimation of PM2.5 measurements in comparison with the reference instruments during the Beijing summer haze period. The regression slopes between the monitors and reference instruments were 2.24 for the summer haze period, 1.58 for the spring haze period, and 1.54 for the summer haze period. Under the extreme air pollution conditions in the Blue Mountains, monitors overestimated PM2.5 in the winter bushfire period but underestimated it in the summer bushfire period. The absolute values of the PM2.5 and CO concentrations from the monitors may vary from the reference instruments; however, they captured the trends and rapid elevation of air pollutants under extreme air pollution conditions. The results of this study demonstrate that low-cost air quality monitors can be used under extreme conditions in different areas for specified purposes such as community, citizen applications, air pollution management, and scientific research.