A novel portable wireless volatile organic compound (VOC) monitoring device with disposable sensors is presented. The device is miniaturized, light, easy-to-use, and cost-effective. Different field tests have been carried out to identify the operational, analytical, and functional performance of the device and its sensors. The device was compared to a commercial photo-ionization detector, gas chromatography-mass spectrometry, and carbon monoxide detector. In addition, environmental operational conditions, such as barometric change, temperature change and wind conditions were also tested to evaluate the device performance. The multiple comparisons and tests indicate that the proposed VOC device is adequate to characterize personal exposure in many real-world scenarios and is applicable for personal daily use.
The present work introduces the use of environmental sensors to assess indoor air quality (IAQ) in combination with human biometrics. The sensor array included temperature, relative humidity, carbon dioxide, and noise monitors. The array was used in a classroom as well as in a vehicle cabin to assess the carbon dioxide production rate of individuals in a closed ventilation environment. Analysis of carbon dioxide production allowed for the quantification of the average metabolic rate of the group of individuals in the classroom, and for one individual in the vehicle cabin. These results yielded a mere 5% difference from the values assessed using commercial metabolic rate instruments, and averaged values from epidemiological studies. The results presented in this work verify the feasibility of determining an individual's metabolic rate using passive environmental sensors; these same sensors are able to provide a metric of IAQ that helps characterize the safety of the environment in which the individual is present.
Volatile organic compounds (VOC) are organic chemicals that have high vapor pressure at regular conditions. Some VOC could be dangerous to human health, therefore it is important to determine real-time indoor and outdoor personal exposures to VOC. To achieve this goal, our group has developed a wearable gas monitor with a complete sensor fabrication and calibration protocol for free-living conditions. Correction factors for calibrating the sensors, including sensitivity, aging effect, and temperature effect are implemented into a Quick Response Code (QR code), so that the pre-calibrated quartz tuning fork (QTF) sensor can be used with the wearable monitor under free-living conditions.
A volatile organic compounds (VOC) sensor based on molecularly imprinted polymer (MIP) modified quartz tuning fork (QTF) has been developed. In this paper, the stability of the modified sensor as a function of the MIP composition, and the temperature effect of the analyte adsorption on the sensing transduction mechanism are evaluated. By mixing MIP and PS together, the stability was improved. A target analyte, o-xylene, was chosen as the VOC model to study the sensor response in a temperature range of 6-40 °C. Langmuir model fitted adsorption isotherms were used for thermodynamic analysis. The changes in the sensitivity of the QTF sensor to temperature rendered different behaviors. For a freshly modified QTF sensor, the adsorption response increased with increasing temperature, while for an aged QTF sensor, the adsorption response decreased with increasing temperature. The results indicated that the enthalpy change of the MIP and PS composition sensing material changes from positive to negative over the course of aging. The characterization of the reaction enabled the definition of sensor calibration conditions and stable sensor performance in field testing conditions.
The development of connected health devices has allowed for a more accurate assessment of a person’s state under free-living conditions. In this work, we use two mobile sensing devices and investigate the correlation between individual’s resting metabolic rate (RMR) and volatile organic compounds (VOCs) exposure levels. A total of 17 healthy, young, and sedentary office workers were recruited, measured for RMR with a mobile indirect calorimetry (IC) device, and compared with their corresponding predicted RMR values from the Academy of Nutrition and Dietetics’ recommended epidemiological equation, the Mifflin–St Jeor equation (MSJE). Individual differences in the RMR values from the IC device and the epidemiological equation were found, and the subjects’ RMRs were classified as normal, high, or low based on a cut-off of ±200 kcal/day difference with respect to the predicted value. To study the cause of the difference, VOCs exposure levels of each participant’s daytime working environment and nighttime resting environment were assessed using a second mobile sensing device for VOCs exposure detection. The results showed that all sedentary office workers had a low VOCs exposure level (<2 ppmC), and there was no obvious correlation between VOCs exposure and the RMR difference. However, an additional participant who was a worker in an auto repair shop, showed high VOCs exposure with respect to the sedentary office worker population and a significant difference between measured and predicted RMR, with a low RMR of 500 kcal/day difference. The mobile sensing devices have been demonstrated to be suitable for the assessment of direct information of human health–environment interactions at free-living conditions.
In order to improve the efficiency of solar air heater, a novel solar air heater with flat micro-heat pipe arrays (FMHPA) is presented in this study. The structure of FMHPA-solar air heater, the working principle and experimental test facility have also been described in detail. The efficiency, the pressure drop and the time constant are determined for the FMHPA-solar air heater. The results showed that the average thermal efficiency of the solar air heater is up to 70% of stable operation and time constant is about 14 minutes. Experimental results indicate better thermal efficiency for FMHPA-solar air heater compared to a traditional flat plate heater.
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