The use of electrochemical sensors for monitoring urban air quality in low-cost, high-density networks

Can commercial low-cost sensor platforms contribute to air quality monitoring and exposure estimates?

Low-cost gas multi-sensor devices could be efficiently used for densifying the sparse urban pollution monitoring mesh if equipped with a reliable calibration able to counter specificity and stability issues of solid-state sensors they rely on. In this work, we present a neural calibration for the prediction of benzene concentrations using a gas multi-sensor device (solid-state) designed to monitor urban environment pollution. The feasibility of a sensor fusion algorithm as a calibrating tool for the multi-sensor device is discussed. A Conventional air pollution monitoring station is used to provide reference data. Results are assessed by means of prediction error characterization throughout a 13 months long interval and discussed. Relationship between training length and performances are also investigated. A neural calibration obtained using a small number of measurement days revealed to be capable to limit the absolute prediction error for more than 6th month, after which seasonal influences on prediction capabilities at low-concentrations suggested the need for a further calibration.

On field calibration of an electronic nose for benzene estimation in an urban pollution monitoring scenario

Environmental Monitoring Ajeet Kaushik,*,†,‡ Rajesh Kumar,*,‡,§ Sunil K. Arya, Madhavan Nair,† B. D. Malhotra, and Shekhar Bhansali‡ †Center for Personalized Nanomedicine, Institute of Neuroimmune Pharmacology, Department of Immunology, Herbert Wertheim College of Medicine, Florida International University, Miami, Florida 33199, United States ‡Bio-MEMS Microsystems Laboratory, Department of Electrical and Computer Engineering, College of Engineering, Florida International University, Miami, Florida 33174, United States Department of Physics, Panjab University, Chandigarh 160014, India Bioelectronics Program, Institute of Microelectronics, A*Star, 11 Science Park Road, Singapore Science Park II, Singapore Department of Biotechnology, Delhi Technological University, Shahbad Daulatpur, Delhi 110042, India

Organic–Inorganic Hybrid Nanocomposite-Based Gas Sensors for Environmental Monitoring

We consider the optimal power scheduling problem for the decentralized estimation of a noise-corrupted deterministic signal in an inhomogeneous sensor network. Sensor observations are first quantized into discrete messages, then transmitted to a fusion center where a final estimate is generated. Supposing that the sensors use a universal decentralized quantization/estimation scheme and an uncoded quadrature amplitude modulated (QAM) transmission strategy, we determine the optimal quantization and transmit power levels at local sensors so as to minimize the total transmit power, while ensuring a given mean squared error (mse) performance. The proposed power scheduling scheme suggests that the sensors with bad channels or poor observation qualities should decrease their quantization resolutions or simply become inactive in order to save power. For the remaining active sensors, their optimal quantization and transmit power levels are determined jointly by individual channel path losses, local observation noise variance, and the targeted mse performance. Numerical examples show that in inhomogeneous sensing environment, significant energy savings is possible when compared to the uniform quantization strategy.

Power scheduling of universal decentralized estimation in sensor networks

This paper describes the development of a gas sensor system to be used as a sensing node to form a dense real-time environmental monitoring network. Moreover, a new auto-calibration method is proposed to achieve the maintenance-free operation of the sensor network. The network connectivity can be used not only for data collection but also for the calibration and diagnosis of the sensors since the measured pollutant concentrations can be easily compared through the network with nearby sensors and governmental monitoring stations. Different pollutant concentrations are usually monitored at different sites. However, a case study on local NO2 distribution has shown that there exists a special condition under which pollutant concentrations become low and uniform in a certain local area. The baseline of the gas sensor response can be adjusted in this special occasion using the pollutant concentration values reported from the neighboring environmental monitoring stations. The experimental result has shown that NO2 concentration can be measured with sufficient accuracy by incorporating appropriate temperature and humidity compensation into calibration curves. Moreover, a case study on auto-calibration demonstrates its effectiveness in keeping the measurement accuracy of the sensor system in long-term operation.

Gas sensor network for air-pollution monitoring

The use of a dynamic gas sensor network is proposed for air pollution monitoring, and its auto-calibration is discussed to achieve the maintenance-free operation. Although the gas sensor outputs generally show drift over time, frequent recalibration of a number of sensors in the network is a laborious task. To solve this problem, instead of the static network proposed in the related works, we propose to realize a dynamic gas sensor network by, e.g., placing sensors on vehicles running on the streets or placing some of them at fixed points and the others on vehicles. Since each sensor in the dynamic network often meets other sensors, calibration of that specific sensor can be performed by comparing the sensor outputs in such occasions. The sensors in the whole network can thus be calibrated eventually. The simulation results are presented to show that adjusting the sensor outputs to the average values of the sensors sharing the same site improves the measurement accuracy of the sensor network.

Dynamic gas sensor network for air pollution monitoring and its auto-calibration

Metropolitan cities in the world have long been suffering from serious air pollution problems. In Tokyo, the high levels of nitrogen oxides and ozone resulting from heavy traffic emission are of the greatest concern. However, the cost and size of the chemical analyzers have limited the number of environmental monitoring stations and, therefore, have resulted in insufficient spatial resolution in the measurement of pollutant distributions. The authors have been proposing a gas distribution analyzing system (GASDAS). The use of gas sensors enables compact and inexpensive sensing systems, and will lead to a significant increase in the density of monitoring sites. As a first step in the development of GASDAS, nitrogen dioxide and ozone monitoring systems have been developed. The experimental results have shown that the low-cost sensor systems with signal compensation features for the change in weather conditions can be used for the quantitative measurement of spatial pollutant distributions.

Sensor-based air-pollution measurement system for environmental monitoring network

Surface potentials of Cu tetra-tert-butyl-phthalocyanine (CuttbPc) Langmuir-Blodgett (LB) films on metal electrodes were measured under photoillumination The surface potential of CuttbPc LB films on Au electrode, positively charged as deposited, decreases by photoillumination, whereas the potential of films on Al and Cr electrodes, negatively charged as deposited, increases A linear relationship was obtained between the work function of metal electrodes and the saturated surface potential of CuttbPc LB films in the dark, and a similar relationship was also suggested under photoillumination These results indicate that electronic charges are exchanged at the interface between metal electrodes and the films until the surface Fermi level of films and the Fermi level of metals mutually coincide The space charge distribution in CuttbPc LB films was determined on the order of nanometer film thickness, and the distribution of the electronic density of states was also determined assuming the presence of both electron donor and acceptor states at the film/metal interface It was concluded that about 1% of CuttbPc molecules contribute the charge exchange and 9–27% of these contributed charges lose the charge exchange by photoillumination Finally, the surface potential decay process was analyzed assuming thermodynamics quasi-equilibrium at the interface

Interfacial Electrostatic Phenomena in Phthalocyanine Langmuir-Blodgett Films under Photoillumination.

There has been growing interest in developing gas sensor systems for environmental applications. The network of a large number of sensors deployed in the field is expected to enable monitoring of local air pollution problems in detail. Toward the development of a gas sensor network, this paper addresses the issue of accuracy in measuring NO2 concentration using a semiconductor gas sensor. Firstly, a sensor cell with a temperature control system is developed. Many gas sensors show variation in their response characteristics with the change in the ambient temperature. The experimental results on the sensor calibration show that the error in the measured NO2 concentration can be effectively reduced by stabilizing the temperature of the gas sensor cell. Secondly, a method for recalibrating the sensor system is discussed. It is shown by the field experiments that the sensor system can be recalibrated by placing the gas sensor system with a reference instrument and readjusting the calibration parameters to minimize the error in the measured concentrations. The proposed recalibration procedure will help to simplify the operation of a number of gas sensors deployed in the sensor network.

Wataru Tsujita

Papers

Gas sensor network for air-pollution monitoring

Dynamic gas sensor network for air pollution monitoring and its auto-calibration

Sensor-based air-pollution measurement system for environmental monitoring network

Interfacial Electrostatic Phenomena in Phthalocyanine Langmuir-Blodgett Films under Photoillumination.

Improvement of Measurement Accuracy in Environmental Monitoring System Based on Semiconductor Gas Sensor