Turbulent Growth and Mixing of Bioaerosols in a Submesoscale Atmospheric Boundary Layer: Challenges and Opportunities

This paper is related to the study of biological living microorganisms that are suspended in the atmosphere, commonly referred to as bio-aerosols. The ecological importance of these microorganisms is associated with diseases in humans, animals and plants, since their opportunity to grow and disperse long distances with the help of wind and precipitation is considerable [1, 2]. Although the living micro-organisms in oceans and in soil have received the primary attention in the past few years, several studies have recently elaborated their active role in the Earth’s atmosphere [3, 4]. Additionally, meteorological variables affect the initial release of these atmospheric bio-aerosols and their overall dispersal, providing a unique opportunity to link the meteorological studies to the field of aerobiology.

Aside from the classical biological and physico-chemical pursuits of aerobiology, questions related to the atmosphere as a habitat of bio-aerosols have been little explored [7]. Recent studies have indicated that wind condition, temperature and moisture availability have strong effects on the concentration and dispersion of atmospheric bio-aerosols [5, 3]. This indicates that for the upcoming era of research on the atmospheric bio-aerosols, one important challenge is to go beyond purely biological (and/or physico-chemical) descriptions towards a comprehensive understanding that includes the effects of realistic meteorological events and the relevant processes on the problem. Consequently, the initiative step is to comprehend the pertinent meteorological processes that affect the spread rate, growth, transport, and the concentration height of such bio-aerosols in an atmospheric boundary layer. These processes include turbulence (i.e. mixing, growth and transport), intermittency and stratification. In the present work, the challenges and opportunities regarding the effects of these processes, especially turbulence and stratification, on the overall dispersal of bio-aerosols in a sub-mesoscale atmospheric boundary layer are discussed.

The bio-aerosols concentration, C, can be modeled using Eq. (1), a standard advection-diffusion equation which includes the effects of atmospheric conditions, where u is the velocity field, k is the diffusion coefficient, Q is the emission rate, and L is the loss rate. The integration of the concentration equation in a numerical model such as WRF-LES or UCSD-LES is straight forward, however, the main challenge is to obtain an accurate mathematical expression for k, Q and L. Generally, the emission rate, Q, and the loss rate, L, depend on the turbulence kinetic energy (TKE), the potential temperature variation, and the moisture availability (q). Therefore, the precursor stage in numerical modeling of atmospheric bio-aerosols is to develop the mathematical expressions, using the existing expertise and data in the field of aerobiology, which can accurately represent the corresponding parameters. It should be noted that there has been somewhat progress in developing similar expressions for the growth rate and the mortality rate of a particular bio-aerosol in [7, 1], but the overall development continuous to defy.

Accurate numerical modeling of atmospheric bio-aerosols is a rich area of research that has not been yet studied. The main objective of interest, in the context of the meteorology, is to precisely explore the effects of turbulence and stratification on the dispersal and the transport of bio-aerosols with a sub-mesoscale atmospheric boundary layer. The choice of a sub-mesoscale atmospheric boundary layer enables an accurate modeling using large eddy simulations, wherein the effects of above-mentioned processes can be carefully investigated and distinguished. This investigation provides a unique opportunity to quantify the corresponding contribution of each process on the transport/dispersal of bio-aerosol and subsequently, underpinning the atmospheric conditions that have the strongest effect on their extinction/survival will contribute a significant progress in the field of aerobiology.

References

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