Carbon Dioxide Aerosols Research Articles

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

Fine particulate matter (PM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sub> ) is a major environmental health risk. Several instruments based on the quartz crystal microbalance (QCM) have been developed for PM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sub> instrument called qEPC-Snow. This instrument consists of a QCM crystal embedded in an electrostatic particle concentrator (EPC) for collection and sensing of PM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sub> 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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 0.9904, corresponding to 0.05667 [(Hz/min)/( μg/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> )] in mass concentration sensitivity for the PM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2.5</sub> representatives. The influence of particle sizes on qEPC-Snow's frequency behaviors will also be discussed in detail.

Effects of Carbon Dioxide Aerosols on the Viability of Escherichia coli during Biofilm Dispersal.

A periodic jet of carbon dioxide (CO2) aerosols is a very quick and effective mechanical technique to remove biofilms from various substrate surfaces. However, the impact of the aerosols on the viability of bacteria during treatment has never been evaluated. In this study, the effects of high-speed CO2 aerosols, a mixture of solid and gaseous CO2, on bacteria viability was studied. It was found that when CO2 aerosols were used to disperse biofilms of Escherichia coli, they led to a significant loss of viability, with approximately 50% of the dispersed bacteria killed in the process. By comparison, 75.6% of the biofilm-associated bacteria were viable when gently dispersed using Proteinase K and DNase I. Indirect proof that the aerosols are damaging the bacteria was found using a recombinant E. coli expressing the cyan fluorescent protein, as nearly half of the fluorescence was found in the supernatant after CO2 aerosol treatment, while the rest was associated with the bacterial pellet. In comparison, the supernatant fluorescence was only 9% when the enzymes were used to disperse the biofilm. As such, these CO2 aerosols not only remove biofilm-associated bacteria effectively but also significantly impact their viability by disrupting membrane integrity.

Removal of different-age biofilms using carbon dioxide aerosols

Many techniques to inactivate or remove biofilms in a wide variety of applications have been developed. Most of these techniques have been applied to biofilms at their initial stage of growth, since they are generally difficult to eradicate once established. The removal of established biofilms has received relatively little attention. In this paper, we report the effectiveness of periodic jets of carbon dioxide aerosols (a mixture of solid and gaseous CO2) to remove Escherichia coli (XL1-blue) biofilms of different ages (up to 3 weeks) on silicon surfaces. The biofilms were not immersed in liquids after growth/rinsing and were treated with the CO2 aerosols. The CO2 aerosols were generated by the adiabatic expansion of high-pressure CO2 gas through a nozzle. The surface area of the biofilms was measured from fluorescent images before and after applying the aerosols for 11, 20, and 30 cycles (each cycle: 8 sec), to compute the removal efficiency. The removal efficiencies decreased with increasing growth time and for the 3-week-old biofilms, they ranged from 91.5 to 99.6% within 4 min. This technique was highly effective for removing both fresh and old biofilms, but some of the biofilm debris such as growth media remained. Further, this CO2 aerosol technique was compared with other removal techniques.

Gas-phase removal of biofilms from various surfaces using carbon dioxide aerosols

The present study evaluated the removal of Escherichia coli XL1-blue biofilms using periodic jets of carbon dioxide aerosols (a mixture of solid and gaseous CO2) with nitrogen gas. The aerosols were generated by the adiabatic expansion of high-pressure CO2 gas through a nozzle and used to remove air-dried biofilms. The areas of the biofilms were measured from scanning electron micrographs before and after applying the aerosols. The removal efficiency of the aerosol treatment was measured with various air-drying times of the biofilms before the treatment, surface materials, and durations of CO2 aerosols in each 8-s aerosol–nitrogen cleaning cycle. Nearly 100% of the fresh biofilms were removed from the various surfaces very reliably within 90 s. This technique can be useful for removing unsaturated biofilms on solid surfaces and has potential applications for cleaning bio-contaminated surfaces.

Combined application of bacterial predation and carbon dioxide aerosols to effectively remove biofilms

This study evaluated predation with Bdellovibrio bacteriovorous and CO2 aerosol spraying to remove fluorescent Escherichia coli biofilms from silicon chips. Initial tests found that 7.5×105 viable E. coli cells were dispersed into the surrounding environment during aerosol treatment. The total number dispersed per test decreased to only 16 for predated biofilms. This is nearly 50,000-fold lower compared to untreated chips and 1000-fold lower compared to chips soaked in HEPES buffer only. Both scanning electron microscopy (SEM) and fluorescent microscopy analyses confirmed that predation alone did not completely eradicate the biofilm population. When used in conjunction with CO2 aerosols, however, no fluorescent signals remained and the SEM pictures showed a pristine surface devoid of bacteria. Consequently, this study demonstrates these two methods can be used with each other to significantly remove biofilms from surfaces while also significantly reducing the likelihood of human exposure to potential pathogens during their removal.

The influence of methane, acetylene and carbon dioxide on the crystallization of supercooled ethane droplets in Titan's clouds

Spectroscopic studies of the homogeneous and heterogeneous crystallization of supercooled ethane aerosol droplets performed under conditions representative of those in Titan's lower atmosphere are presented. Pure ethane aerosols and both internally- and externally-mixed ensembles of ethane/acetylene and ethane/carbon dioxide aerosols were generated in a bath gas cooling cell and their freezing dynamics monitored using infrared absorption spectroscopy. A detailed overview of the spectroscopic signatures of pure ethane and mixed ethane/acetylene and ethane/carbon dioxide aerosols and their phase-dependence is provided. The ice-nucleating efficiencies of acetylene and carbon dioxide aerosols were compared, as were the efficiencies of freezing via an immersion or contact freezing mechanism. The spectral data provided will be of significant use for remote sensing applications, while the nucleation studies have important consequences for models of Titan's ethane clouds.

Removal of biofilms using carbon dioxide aerosols

The formation of biofilm (bacterial film) has been serious concerns in a wide variety of applications, because it is involved in many human and device-associated infections. We present a novel method of effectively and rapidly removing Escherichia coli (XL1-blue) biofilm from a silicon chip, using carbon dioxide aerosols. The aerosols were generated by adiabatic expansion of a high-pressure CO 2 gas through a nozzle and they were applied to biofilms that had been grown for 24 h on silicon chips. We measured the percentage area cover of the bacteria from the scanning electron micrographs taken before and after applying the aerosols. The decrease in the percentage area cover, caused by the aerosols, was measured as several parameters such as the distance between the nozzle and the chip, the angle of the nozzle axis relative to the horizontal, CO 2 stagnation pressure, rinsing solution, the aerosol exposure time, and drying time were varied. Nearly 100% of the biofilms were removed within 90 s whether the chip surfaces were very humid (no-drying) or dry (7 h-drying) immediately before applying the aerosols. This method has potential application to cleaning of a wide variety of bio-contaminated surfaces.

Investigation of the interaction between a hypersonic air stream and a carbon dioxide aerosol

A detailed investigation is made of the interaction between a hypersonic vibrationally excited donor gas and a carbon dioxide aerosol stream with a view to improving the energy characteristics of a gasdynamic CO2 laser. The analysis shows that rapid (within times shorter than the relaxation time of the upper active level) mixing of the evaporating aerosol and the vibrationally excited gas is possible as a result of this interaction. For a planar flow geometry with symmetrical aerosol injection, the transverse dimension of the active medium may be 20 cm for a hypersonic nozzle with a throat cross section ~1 mm high. The conditions under which there were no gas-dynamic perturbations in the mixing zone and the active medium was optically homogeneous were determined. A CO2 aerosol generator was developed with a solid particle size distribution function close to the optimal. An experimental investigation was made of the interaction between the streams using a system with a conical hypersonic nozzle for the air and perpendicular injection of the aerosol. The experimental results broadly agreed with the theoretical predictions. A CO2 laser radiation gain close to the calculated value was obtained in the excited air-carbon dioxide aerosol mixing zone.