This Small Business Innovation Research Phase I project aims to develop low-cost light-weight miniaturized instruments, based on micro-electro-mechanical resonant nanobalances, for real-time monitoring of concentration, and size distribution of airborne micro/nano-particles. Aerosol particles in the diameter range from nanometers to microns play important roles in air quality, human health, visibility in the atmosphere, the radiation balance of the earth (climate change), and stratospheric ozone depletion. Aerosol contaminants in industrial cleanrooms can limit the size and quality of integrated circuit elements. There has not been enough progress in light weight and low-cost aerosol particle monitoring technologies over the past decades and the existing technologies cannot address all the existing needs (e.g. in semiconductor industry). The innovative approach proposed here integrates micro/nanoscale electromechanical resonant balances within miniaturized micro-orifice cascade impactors. Cascade impactors separate particles in the air flow based on their size and deposit them on designated micro/nanoscale electromechanical resonant mass balances performing real time mass measurement. The proposed instrument can sample the surrounding air, separate airborne particles into several size ranges, and measure the individual and/or cumulative mass of particles in each size range.
The broader impact/commercial potential of this project is development of a more capable and cost effective category of airborne particulate monitors. Currently available particulate monitoring systems can be divided into two major categories: 1. Laser-based counters, and 2. Inertial impactors. Other than being relatively costly and bulky and their need for frequent calibration, lower cost laser-based counters can only detect particles with diameters as small as 0.3µm. Inertial impactors on the other hand can collect particles with diameters as small as a few nanometers, but such systems generally offer no automated or real time processing capability. Collected particulate matter in such systems is manually weighed after sampling a large enough volume of air. Successful development of the proposed technology allows real time monitoring of nanoscale airborne particles down to a few nanometers size range using low cost, light weight instruments. The target market for the proposed instruments can be divided into two major sections: a) Cleanroom/controlled environment monitoring. This includes semiconductor/micro-manufacturing and pharmaceutical cleanrooms, operating rooms, etc.; b) Personal particulate mass exposure monitors for work place safety in industrial environments prone to excessive micro/nanoparticulate generation and dispersion. This includes Nanomaterials processing plants, mines (e.g. coal mines), metal processing plants, etc.
Airborne particulate matter (PM) is comprised of tiny pieces of solid or liquid matter suspended in the air. For example, fog or hazy skies are a result of water droplets or other particles in the atmosphere. Sources of particulate matters can be manmade (e.g. diesel engine) or natural (e.g. volcano). As we inhale the air and along with it all the suspended PM, larger particles (generally larger than 10μm) are filtered in the nose and throat via cilia and mucus. However, smaller particles can settle in the bronchi and lungs and cause serious health issues. Similarly, particles smaller than 2.5 micron that are often invisible, tend to penetrate into the gas exchange regions of the lung, and finally very small particles (< 100 nanometers) may pass through the lungs and affect other organs. The proven health effects caused by excessive levels of PM in the air include asthma, cancers, cardiovascular issues, respiratory diseases and birth defects. PM exposure is a very serious issue with tangible effects in industries that deal with processes and materials generating excessive amounts of dust. Therefore, a number of government agencies and organizations set standards, limits, monitoring and reporting requirements to protect the industry workers. For example, respirable crystalline silica is one of the most common categories of harmful PM that is well known for its association with silicosis. Silicosis (previously known as miner's phthisis, grinder's asthma, potter's rot and other occupation-related names) is a serious disease where scar tissue forms in the lungs and reduces the ability to extract oxygen from the air. Industries with the largest numbers of workers potentially exposed to respirable crystalline silica include coal and lignite mining, metal and nonmetallic minerals mining, oil and gas extraction, masonry and stonework, concrete, agriculture, gypsum, and plaster products, medical and dental laboratories, metal casting, glass products, ceramics, clay and pottery, structural demolition, etc. This SBIR project aims to develop small size, light-weight, and affordable personal Particulate Matter (PM) dosimeters that can help protect individuals in high risk environments against over exposure to PM. The battery powered instrument almost the size of a fountain pen can be clipped onto clothing and freely carried around. The instrument can sample the surrounding air, separate airborne particles into several size ranges, and measure the mass of particulate matter collected from the air sample in each size range. Under the Phase I award, a number of sensor system prototypes were designed, fabricated, and tested showing promising performance. At the heart of such systems is the proprietary technology combining ultra-sensitive microscale mass balances with micro-nozzles that manipulate the air flow. Properly designed and meticulously positioned micronozzles help separate particles in the air flow based on their size and deposit particles within each size range onto different microscale mass sensors. The mass sensors are microscale electromechanical resonators that can detect masses as small as a few pico-grams. Analysis of the mass sensor response can determine the deposited mass and therefore the mass concentration of particles with different sizes in the sampled air.
