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ABSTRACT
Aerosol sampling and identification is vital for the assessment and control of particulate matter pollution, airborne pathogens, allergens, and toxins and their effect on air quality, human health, and climate change. In situ analysis of chemical and biological airborne components of aerosols on a conventional filter is challenging due to dilute samples in a large collection region. We present the design and evaluation of a micro-well (µ-well) aerosol collector for the assessment of airborne particulate matter (PM) in the 0.5–3 µm size range. The design minimizes particle collection areas allowing for in situ optical analysis and provides an increased limit of detection for liquid-based assays due to the high concentrations of analytes in the elution/analysis volume. The design of the collector is guided by computational fluid dynamics (CFD) modeling; it combines an aerodynamic concentrator inlet that focuses the aspirated aerosol into a narrow beam and a µ-well collector that limits the particle collection area to the µ-well volume. The optimization of the collector geometry and the operational conditions result in high concentrations of collected PM in the submillimeter region inside the µ-well. Collection efficiency experiments are performed in the aerosol chamber using fluorescent polystyrene microspheres to determine the performance of the collector as a function of particle size and sampling flow rate. The collector has the maximum collection efficiency of about 75% for 1 µm particles for the flow rate of 1 slpm. Particles bigger than 1 µm have lower collection efficiencies because of particle bounce and particle loss in the aerodynamic focusing inlet. Collected samples can be eluted from the device using standard pipettes, with an elution volume of 10–20 µL. The transparent collection substrate and the distinct collection region, independent of particle size, allows for in situ optical analysis of the collected PM.
© 2017 American Association for Aerosol Research
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Nomenclature
| Nomenclatures | ||
| Cc | = | Cunningham correction factor |
| D | = | diameter of the first stage of the AF inlet (m) |
| D* | = | optimum inlet diameter (m) |
| Dc | = | characteristic dimension of the impactor (m) |
| Q | = | volumetric flowrate (m3/s) |
| Stk* | = | optimum Stokes number |
| U | = | area-average flow velocity magnitude (m/s) |
| dp | = | particle diameter (m) |
| τ | = | relaxation time (s) |
| η | = | dynamic viscosity (Pa·s) |
| ρp | = | particle density (kg/ m3) |
| ρ | = | density of the air (kg/m3) |
| ε | = | collection efficiency |
Funding
This research was funded in part by a grant from the National Institute of Environmental Health Sciences (1R21ES024715) and by a grant from the National Institute of Biomedical Imaging and Bioengineering (U01 EB021923).
