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

Nhan Dinh Ngo,Jaesung Jang

doi:10.1109/access.2021.3090401

Nhan Dinh Ngo, Jaesung Jang

Open Access

https://doi.org/10.1109/access.2021.3090401

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Abstract

Fine particulate matter (PM 2.5 ) is a major environmental health risk. Several instruments based on the quartz crystal microbalance (QCM) have been developed for PM 2.5 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 PM 2.5 instrument called qEPC-Snow. This instrument consists of a QCM crystal embedded in an electrostatic particle concentrator (EPC) for collection and sensing of PM 2.5 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 100-nm and 2- μm polystyrene latex microspheres as PM 2.5 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 PM 2.5 representatives. The influence of particle sizes on qEPC-Snow's frequency behaviors will also be discussed in detail.

Highlights

Atmospheric pollution has several detrimental impacts on human health and is a significant concern for the global community [1]
The measurement of frequency shifts due to added mass is a primary consideration of any quartz crystal microbalance (QCM)-based instrument
Removals of deposited particles from the crystal electrodes are of great interest for reusing the crystal because they significantly affect the long-term measurement of qEPC-Snow

Summary

Introduction

Atmospheric pollution has several detrimental impacts on human health and is a significant concern for the global community [1]. Particulate matter (PM), a major air pollutant, originates from several sources such as traffic, fuel burning, natural dust, and industrial activities [2]. Aerodynamic diameter of 2.5 μm or less (PM2.5) has attracted significant attention [3] because these fine particles can pass through the filtration of nose hairs and penetrate deeply into the lung [4]. PM2.5 can carry toxic matter such as viruses and bacteria into a human lung, increasing the prevalence of the respiratory disease [5], [6] and necessitating measuring its concentration level. Many instruments for PM mass concentration measurement using principles such as radiometric

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