Design and Validation of a portable sampler to monitor pollens at street level in the ambient environment

Abstract

In the ambient environment where gases and various particles coexist, pollen is a chief biological airborne particle among atmospheric bioaerosols. Despite its significance, pollen surveillance in many countries including India is overlooked as most of the air quality monitoring, predominantly targets PM2.5, PM10, or other gaseous pollutants. Pollens are not only vital for plant reproduction but they interact with various atmospheric elements, trigger allergies, influence genetic exchange and cause environmental shifts by fostering microorganism transmission. Despite their profound impacts, the epidemiological effects of pollens remain underexplored. Majority of the pollens aggravate diseases like asthma or COPD in human beings and, therefore the investigative studies on pollens become crucial for disease management. The sampling of pollens involves multiple parameters e.g., wind speed, turbulence, and orientation of sampler, affecting their concentrations. Suction-based impaction pollen samplers offer promising pollen sampling due to their adaptable cut points and high throughput. However, if such suction-based samplers are designed to match human breathing rates of 12-16 LPM and a D50 of 2 µm, the retrieval of pollens is efficiently optimized. In this work, a rectangular slit-based pollen sampler was designed after carrying out extensive numerical modelling for creating a 3D design of the sampler. Further, the Computational Fluid Dynamic (CFD) employing Poly-Hexcore volume meshing, and a k-w turbulence model combined with the Discrete Phase Model (DPM). was used to validate the design of the sampler., The DPM includes particle sizes ranging from 2 – 100 µm with simulations carried out in two regions i.e., solid (slide) and fluid (air). The slide's boundary condition was set as ‘trap’ since it was coated with a sampling medium to capture pollens. Further, inlet and outlet boundary conditions were set as ‘escape’. The efficiency of pollen collection as observed from the simulations, ranged between 60% - 100%, gauged through particle trajectory and streamlines. Pollen collection efficiency was found to increase when staggered inlet and outlet mass flow geometry were used. Moreover, the use of a trapping sampling medium restricted particle jump-off, altering the particle cut-off point towards smaller sizes. This shift, while enhancing capture efficiency, also influenced the particle size range the sampler can effectively trap. In summary, the pollen sampler designed in this work exhibited a better collection efficiency compared to traditional samplers and was also representative of the pollen inhalation rate of human beings. Further, field testing was also done for the sampler to see the presence of pollen in ambient air.