Finite element simulation of Love wave sensor for the detection of volatile organic gases

The 3D finite element (3D-FE) simulation and analysis of Love wave sensors based on PIB layers/SiO2/ST-90°X quartz structure, as well as the investigation of coupled resonance effect on the acoustic properties of the devices, are presented in this paper. The mass sensitivity of the basic Love wave device with SiO2 guiding layers solved analytically. And the highest mass sensitivity of 128 m2/kg is obtained as h s/λ =0.175. The sensitivity of the Love wave sensors for sensing VOCs is greatly improved due to the presence of coupled resonance induced by the PIB nanorods on the device surface. The frequency shifts of the sensor corresponding to CH2Cl2, CHCl3, CCl4, C2Cl4, CH3Cl and C2HCl3 with the concentration of 100 ppm are 1.431 kHz, 5.507 kHz, 13.437 kHz, 85.948 kHz, 0.127 kHz and 17.879 kHz, respectively. The viscoelasticity influence of sensitive material on the characteristics of SAW sensors is also studied. Taking account of the viscoelasticity of PIB layers, the sensitivities of SAW sensors with the PIB film and PIB nanorods decay in different degree. The gas sensing property of Love wave sensor with PIB nanorods is superior to that of the PIB films. Meanwhile, the Love wave sensors with PIB sensitive layers show good selectivity to C2Cl4, making it an ideal selection for gas sensing applications.

Ppb-Level Butanone Sensor Based on ZnO-TiO2-rGO Nanocomposites

In this paper, ZnO-TiO2-rGO nanocomposites were successfully synthesized by the hydrothermal method. The morphology and structure of the synthesized nanomaterials were characterized by SEM, XRD, HRTEM, and XPS. Butanone is a typical ketone product. The vapors are extremely harmful once exposed, triggering skin irritation in mild cases and affecting our breathing in severe cases. In this paper, the gas-sensing properties of TiO2, ZnO, ZnO-TiO2, and ZnO-TiO2-rGO nanomaterials to butanone vapor were studied. The optimum operating temperature of the ZnO-TiO2-rGO sensor is 145 °C, which is substantially lower than the other three sensors. The selectivity for butanone vapor is greatly improved, and the response is 5.6 times higher than that of other organic gases. The lower detection limit to butanone can reach 63 ppb. Therefore, the ZnO-TiO2-rGO sensor demonstrates excellent gas-sensing performance to butanone. Meanwhile, the gas-sensing mechanism of the ZnO-TiO2-rGO sensor to butanone vapor was also analyzed.

Dynamic infrared gas analysis from longleaf pine fuel beds burned in a wind tunnel: observation of phenol in pyrolysis and combustion phases

Pyrolysis is the first step in a series of chemical and physical processes that produce flammable organic gases from wildland fuels that can result in a wildland fire. We report results using a new time-resolved Fourier transform infrared (FTIR) method that correlates the measured FTIR spectrum with an infrared thermal image sequence, enabling the identification and quantification of gases within different phases of the fire process. The flame from burning fuel beds composed of pine needles (Pinus palustris) and mixtures of sparkleberry, fetterbush, and inkberry plants was the natural heat source for pyrolysis. Extractive gas samples were analyzed and identified in both static and dynamic modes synchronized to thermal infrared imaging: a total of 29 gases were identified including small alkanes, alkenes, aldehydes, nitrogen compounds, and aromatics, most previously measured by FTIR in wildland fires. This study presents one of the first identifications of phenol associated with both pre-combustion and combustion phases using ca. 1 Hz temporal resolution. Preliminary results indicate ∼2.5× greater phenol emissions from sparkleberry and inkberry compared to fetterbush, with differing temporal profiles.

Heterogeneous uptake of NH3 on ambient PM2.5 in Beijing and Shijiazhuang: Possible influence of aerosol acidity

<p>Ammonium salts (NH<sub>4</sub><sup>+</sup>) is the important component of PM<sub>2.5</sub> and has a significant impact on air quality, climate, human health, and natural ecosystems. The contribution of NH<sub>4</sub><sup>+</sup> to PM<sub>2.5</sub> is increasing at urban sites. Ammonia (NH<sub>3</sub>) with global emissions estimated at greater than 33 Tg(N) Yr<sup>-1</sup> is the only precursor of particulate NH<sub>4</sub><sup>+</sup> in the atmosphere. Thus, it is important to understand the conversion kinetics from NH<sub>3</sub> to NH<sub>4</sub><sup>+</sup> in the atmosphere. However, the uptake coefficient of NH<sub>3</sub> (γ<sub>NH3</sub>) on aerosol particles are scarce at the present time. In this work, we reported the γ<sub>NH3</sub> on ambient PM<sub>2.5</sub> in Beijing and Shijiazhuang in China. The γ<sub>NH3</sub> values on ambient PM<sub>2.5</sub> are (1.13±12.4)×10<sup>-4</sup> and (6.88±40.7)×10<sup>-4</sup> in Shijiazhuang and Beijing, respectively. They are significantly lower than those on sulfuric acid droplet (0.1-1), aqueous surface (~5×10<sup>-3</sup>-0.1) and acidified secondary organic aerosol (~10<sup>-3</sup>-~10<sup>-2</sup>), while are comparable with that on ice surface (5.3±2.2 ×10<sup>-4</sup>) and on sulfuric acid in the presence of organic gases (2×10<sup>-4</sup>-4×10<sup>-3</sup>). An annual increase of γ<sub>NH3</sub> in the statistic sense is observed and the possible reason related to the aerosol acidity has also been discussed.</p>

Biodegradation by bacteria in clouds: an underestimated sink for some organics in the atmospheric multiphase system

Water-soluble organic compounds represent a significant fraction of total atmospheric carbon. The main oxidants towards them in the gas and aqueous phases are OH and NO3 radicals. In addition to chemical solutes, a great variety of microorganisms (e.g., bacteria, viruses, fungi) have been identified in cloud water. Previous lab studies suggested that for some organics, biodegradation by bacteria in water is comparable to their loss by chemical processes. We perform model sensitivity studies over large ranges of biological and chemical process parameters using a box model with a detailed atmospheric multiphase chemical mechanism and biodegradation processes to explore the importance of biodegradation of organics in the aqueous phase. Accounting for the fact that only a small number fraction of cloud droplets (∼0.0001–0.001) contains active bacterial cells, we consider only a few bacteria-containing droplets in the model cloud. We demonstrate that biodegradation might be most efficient for water-soluble organic gases with intermediate solubility (∼104≤KH(eff) [M atm−1] ≤106, e.g., formic and acetic acids). This can be explained by the transport limitation due to evaporation of organics from bacteria-free droplets to the gas phase, followed by the dissolution into bacteria-containing droplets. For cloud condensation nuclei (CCN)-derived compounds, such as dicarboxylic acids, the upper limit of organic loss by biodegradation can be approximated by the amount of organics dissolved in the bacteria-containing droplets (<0.1 %). We compare results from our detailed drop-resolved model to simplified model approaches, in which (i) either all cloud droplets are assumed to contain the same cell concentration (0.0001–0.001 cell per droplet), or (ii) only droplets with intact bacterial cells are considered in the cloud (liquid water content ∼10-11 vol / vol). Conclusions based on these approaches generally overestimate the role of biodegradation, particularly for highly water-soluble organic gases. Our model sensitivity studies suggest that current atmospheric multiphase chemistry models are incomplete for organics with intermediate solubility and high bacterial activity.