Development of Three-Stage Bioaerosol Sampler for Size-Selective Sampling.

In this study, a three-stage bio-aerosol sampler with a sampling flow rate of 170 L/min was designed and fabricated for sampling the bio-aerosols released during human breathing and coughing, and its performance was evaluated. The sampler was constructed using a cyclone separator with a cutoff size of 2.5 µm as a preseparator, a multinozzle virtual impactor with a cutoff size of 0.34 µm as an aerosol concentrator, and a Bio-Sampler, which is a commercial product, for collecting bio-aerosols in a collection fluid. The collection efficiency of the sampler was evaluated through simulations and experiments. Only particles with sizes of 0.1-4 µm were selectively collected in the collection fluid. Bacteriophage bio-aerosols were sampled using the developed sampler and ACD-200 Bobcat sampler, which is a commercial product. The amounts of collected bacteriophages were compared using the polymerase chain reaction (PCR) technique. The sampling performance of the developed sampler was similar to that of the ACD-200 Bobcat sampler. Moreover, the developed sampler showed its ability to sample bio-aerosols of a specific size range and collect them directly in a collection fluid for the PCR analysis. Therefore, the developed sampler is expected to be useful for indoor environmental monitoring by effectively sampling the bio-aerosols released indoors during human breathing and coughing.

Towards the World's Smallest Gravimetric Particulate Matter Sensor: A Miniaturized Virtual Impactor with a Folded Design.

The increasing air pollution across the globe has given rise to a global health crisis that is increasing at an alarming rate. Every year, millions of people lose their lives due to health risks caused by air pollutants. Hence, there is a pressing need for better solutions to accurately measure the amount of air pollution. This work is aimed at designing a highly compact, accurate, low-cost, self-resettable, and easy-to-use gravimetric-based particulate matter sensor solution for portable applications. Previous attempts have failed to realize true miniaturization, due to the size constraints of the virtual impactor needed-a mechanism that segregates the particulate matters based on their sizes. Our complete particulate matter sensor solution consists of three components (i) a piezoelectric resonating membrane, (ii) a virtual impactor, and (iii) a thermophoretic mechanism to reset the sensor. This paper presents a novel design of the virtual impactor, based on a folded configuration. This helps realize the entire system in a volume of 20 mm × 20 mm × 10 mm. We report here the design, working principles, fabrication, and experimental results of the virtual impactor.

Innovations in air sampling to detect plant pathogens.

Many innovations in the development and use of air sampling devices have occurred in plant pathology since the first description of the Hirst spore trap. These include improvements in capture efficiency at relatively high air-volume collection rates, methods to enhance the ease of sample processing with downstream diagnostic methods and even full automation of sampling, diagnosis and wireless reporting of results. Other innovations have been to mount air samplers on mobile platforms such as UAVs and ground vehicles to allow sampling at different altitudes and locations in a short space of time to identify potential sources and population structure. Geographical Information Systems and the application to a network of samplers can allow a greater prediction of airborne inoculum and dispersal dynamics. This field of technology is now developing quickly as novel diagnostic methods allow increasingly rapid and accurate quantifications of airborne species and genetic traits. Sampling and interpretation of results, particularly action-thresholds, is improved by understanding components of air dispersal and dilution processes and can add greater precision in the application of crop protection products as part of integrated pest and disease management decisions. The applications of air samplers are likely to increase, with much greater adoption by growers or industry support workers to aid in crop protection decisions. The same devices are likely to improve information available for detection of allergens causing hay fever and asthma or provide valuable metadata for regional plant disease dynamics.

Designing a Microfluidic Chip Driven by Carbon Dioxide for Separation and Detection of Particulate Matter.

Atmospheric particulate pollution poses a great danger to the environment and human health, and there is a strong need to develop equipment for collecting and separating particulate matter of different particle sizes to study the effects of particulate matter on human health. A virtual impactor is a particle separation device based on the principle of inertial separation which provides scientific guidance for identifying the composition characteristics of particles. Much existing virtual impactor research focuses on the design of structural dimensions with little exploration of the effect of fluid properties on performance. In this paper, a microfluidic chip with a cutoff diameter of 1.85 µm was designed based on computational fluid dynamics and numerically simulated via finite element analysis to analyze important parameters such as inlet flow rate, splitting ratio and fluid properties. By numerical simulation of the split ratio, we found that the obtained collection efficiency curves could not be combined into one characteristic curve by the Stk0.5 scaling method. We therefore propose a modified Stokes number equation for predicting the cutoff diameter at different splitting ratios. The collection efficiency curves of different fluids as microfluidic chip media were plotted, and the results show that the cut particle size was reduced from 2.5 µm to 1.85 µm after replacing conventional fluid air with CO2 formed by dry ice sublimation. This is a decrease of approximately 26%, which is superior to other existing methods for reducing the cutoff diameter.

Computational Fluid Dynamics Study of the Effects of Temperature and Geometry Parameters on a Virtual Impactor.

The virtual impactor, as an atmospheric particle classification chip, provides scientific guidance for identifying the characteristics of particle composition. Most of the studies related to virtual impactors focus on their size structure design, and the effect of temperature in relation to the dynamic viscosity on the cut-off diameter is rarely considered. In this paper, a new method that can reduce the cut-off particle size without increasing the pressure drop is proposed. Based on COMSOL numerical simulations, a new ultra-low temperature virtual impactor with a cut-off diameter of 2.5 µm was designed. A theoretical analysis and numerical simulation of the relationship between temperature and the performance of the virtual impactor were carried out based on the relationship between temperature and dynamic viscosity. The effects of inlet flow rate (Q), major flow channel width (S), minor flow channel width (L) and split ratio (r) on the performance of the virtual impactor were analyzed. The collection efficiency curves were plotted based on the separation effect of the new virtual impactor on different particle sizes. It was found that the new ultra-low temperature approach reduced the PM2.5 cut-off diameter by 19% compared to the conventional virtual impactor, slightly better than the effect of passing in sheath gas. Meanwhile, the low temperature weakens Brownian motion of the particles, thus reducing the wall loss. In the future, this approach can be applied to nanoparticle virtual impactors to solve the problem of their large pressure drop.

Real-time measurements of mineral dust concentration in coarse particulate matter (PM10-2.5) by employing a novel optical-based technique in Los Angeles.

As a primary component of coarse particulate matter (PM), ambient mineral dust has been linked to adverse health effects. Los Angeles, the largest metropolitan urban area of the United States, is impacted by both windblown and localized sources of mineral dust, often internally mixed with black carbon. The estimation of mineral dust concentrations with a high time resolution becomes critical in improving our understanding of its sources and temporal trends. Using Aethalometers combined with a high-volume virtual impactor (VI) to enrich coarse (2.5

A miniature system for separating aerosol particles and measuring mass concentrations.

We designed and fabricated a new sensing system which consists of two virtual impactors and two quartz-crystal microbalance (QCM) sensors for measuring particle mass concentration and size distribution. The virtual impactors utilized different inertial forces of particles in air flow to classify different particle sizes. They were designed to classify particle diameter, d, into three different ranges: d<2.28 µm, 2.28 µm≤d≤3.20 µm, d>3.20 µm. The QCM sensors were coated with a hydrogel, which was found to be a reliable adhesive for capturing aerosol particles. The QCM sensor coated with hydrogel was used to measure the mass loading of particles by utilizing its characteristic of resonant frequency shift. An integrated system has been demonstrated.

Design and Analysis of Particulate Matter Air-Microfluidic Grading Chip Based on MEMS.

Atmospheric particulate matter (PM) air-microfluidic grading chip is the premise for realizing high-precision PM online monitoring. It can be used as an indispensable basis for identifying pollution sources and controlling inhalable harmful substances. In this paper, based on aerodynamic theory and COMSOL numerical analysis, a two-stage PM air-microfluidic grading chip with cut-off diameters of 10 µm and 2.5 µm was designed. The effects of chip inlet width (W), main flow width (L), second channel width (S), and split ratio (Q1/Q) on PM classification efficiency were analyzed, and optimized design parameters were achieved. The collection efficiency curves were plotted according to PM separation effects of the chip on various particle sizes (0.5-15 µm). The results indicate that the chip has good separation effect, which provides an efficient structural model for the PM micro-fluidization chip design.

Microfluidic and Micromachined/MEMS Devices for Separation, Discrimination and Detection of Airborne Particles for Pollution Monitoring.

Most of the microfluidics-related literature describes devices handling liquids, with only a small part dealing with gas-based applications, and a much smaller number of papers are devoted to the separation and/or detection of airborne inorganic particles. This review is dedicated to this rather less known field which has become increasingly important in the last years due to the growing attention devoted to pollution monitoring and air quality assessment. After a brief introduction summarizing the main particulate matter (PM) classes and the need for their study, the paper reviews miniaturized devices and/or systems for separation, detection and quantitative assessment of PM concentration in air with portable and easy-to-use platforms. The PM separation methods are described first, followed by the key detection methods, namely optical (scattering) and electrical. The most important miniaturized reported realizations are analyzed, with special attention given to microfluidic and micromachined or micro-electro-mechanical systems (MEMS) chip-based implementations due to their inherent capability of being integrated in lab-on-chip (LOC) type of smart microsystems with increased functionalities that can be portable and are easy to use. The operating principles and (when available) key performance parameters of such devices are presented and compared, also highlighting their advantages and disadvantages. Finally, the most relevant conclusions are discussed in the last section.

[Application of a Two-stage Virtual Impactor in Measuring of PM10 and PM2.5 Emissions from Stationary Sources].

Recently, the Ministry of Environmental Protection of China started the development of emission inventories in fifteen Chinese cities. It includes the esmission of PM10 and PM2.5 from stationary sources. However, there is no national standard method in China for stationary source PM10 and PM2.5 sampling. In this study, a two-stage virtual impactor was developed for sampling PM10 and PM2.5 from stationary sources. Its performance was evaluated for four types of sataionary sources, i.e., coal-fired power plant, waste incineration, circulating fluid bed, and converter steelmaking. These four tested emission sources were equipped with high efficiency PM control devices. PM2.5 mass concentrations measured in the chimneys of these emission sources were (0.93±0.03), (3.3±0.65), (0.59±0.04), and (0.15±0.04) mg·m-3, respectively, while the PM10 mass concentrations were (1.13±0.11), (6.9±0.86), (1.12±0.16), and (0.43±0.15) mg·m-3, respectively.