Aerosol mass concentration measurements: Recent advancements of real-time nano/micro systems

As excessive exposure to airborne particulate matter (PM) results in adverse health effects, the development of real-time PM monitoring is highly relevant. The objective of this article is to broadly review the current state-of-the-art on aerosol mass-concentration measurement, and on real-time monitoring systems. Widely used systems are bulky, time consuming or expensive to maintain. Over the past decade, sensor developments have shown the following features: portable, inexpensive, and suitable for monitoring real-time measurements. PM monitoring systems can be easily accessed through the development of nano or micro scale systems. These sensors can be integrated into conventional electronic devices in order to demonstrate their capabilities to provide real-time and ultra-sensitive measurements. However, reducing the size of the systems reveals strengths and limitations. With respect to mass concentration measurement, we distinguish a generation of “first” and “second” systems based on their different sizes. We examine the main characteristics of PM systems as follows: type of instrument devices (either bulky or nano/microfabricated), sampling method, real-time monitoring measurement capability, sensitivity, and reliability of the new generation of sensors. Acoustic mass sensors are compared to nano and micro scale electromechanical sensors. While the miniature sensors still need to be matured and integrated into appropriate aerosols sampling methods, the physical constraints and the mass measurement capability of these sensors are investigated. Nano and micro sensors can be promising tools for aerosol mass concentration measurement systems, particularly in terms of sensitivity. A PM monitoring system can be achieved by combining an appropriate sampling method with nano or micro sensors. This review suggests different types of sensors that can be used as an appropriate option for PM monitoring, and suggests that fixed and reliable bulky systems are soon to be replaced by nano and micro scale sensors. Nevertheless, the latter systems should be further optimized in order to exhibit more accurate measurements.