Long-Term Measurement of PM2.5 Mass Concentration Using an Electrostatic Particle Concentrator-Based Quartz Crystal Microbalance Integrated With Carbon Dioxide Aerosol Jets for PM Sensing in Remote Areas

Abstract

Fine particulate matter (PM2.5) is a major environmental health risk. Several instruments based on the quartz crystal microbalance (QCM) have been developed for PM2.5 measurement because of their accurate, sensitive, real-time, and low-cost mass measurements. However, prolonged or non-uniform deposition on the quartz crystal can cause nonlinear responses between frequency shifts and mass deposition, and its frequent manual cleaning with wet sponges is required. These disable long-term measurements of the instruments, thus limiting their applications in remote areas. Herein, we present a new PM2.5 instrument called qEPC-Snow. This instrument consists of a QCM crystal embedded in an electrostatic particle concentrator (EPC) for collection and sensing of PM2.5 and a carbon dioxide aerosol (snow) jet unit for residue-free, rapid, effective, and non-destructive cleaning of the crystal. Laboratory tests were conducted with aerosolized 100nm and 2-µm polystyrene latex microspheres as PM2.5 representatives to evaluate (i) frequency responses and (ii) mass sensitiveness of qEPC-Snow, (iii) particle removal efficiencies, and (iv) reuse of the used crystals. Experimental results demonstrated high removal efficiencies (approximately 99.9% for both particle sizes) and statistical similarity between the initial and cleaned QCM crystals in the frequency shift-mass deposition relationship, thereby enabling measurement for more than one month without demounting the crystals. The mass sensitivity was 57.34 (Hz/µg) with R 2 = 0.9904, corresponding to 0.05667 [(Hz/min)/(µg/m 3 )] in mass concentration sensitivity for the PM2.5 representatives. The influence of particle sizes on qEPC-Snow's frequency behaviors will also be discussed in detail.INDEX TERMS Carbon dioxide snow cleaning, electrostatic particle concentrator, PM2.5 mass concentration measurement, quartz crystal microbalance, remote sensing

Environmental Justice and the Use of Artificial Intelligence in Urban Air Pollution Monitoring

“…This method naturally has limitations in online applications. Currently, there are analyzers based on a Quartz Crystal Microbalance (QCM) [36], which is a thin layer of quartz crystal less than 1 mm thick. Gold films deposited on both sides of the quartz layer serve as electrodes, through which oscillations pass with a frequency typical of quartz.…”

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“…In addition, as it uses a radiometric source to emit β particles, it is expensive and bulky. In comparison with the above methods, acoustic sensing technology, e.g., using a QCM sensor, has the advantages of low cost, real-time measurement, compact size, and easy acquisition. − Another important advantage of using QCM sensing is that it can directly convert the PM mass to the sensor frequency shift. Moreover, the QCM has a relatively low temperature coefficient of frequency (TCF), , leading to good thermal stability for precision sensing applications.…”