Bioaerosols ice nucleation
Bioaerosols, a group of organic aerosols ranging from ~ 10 nm to 100 脗碌m, are airborne particles or large molecules that are either alive, carry living organisms or are released from living organisms (e.g., bacteria, fungi, virus, pollen, cell debris, and biofilms; Fig 1.5). The presence of various types of bioaerosols in indoor air, in the troposphere and even in the stratosphere has long been established. Although most research on bioaerosols has focused on issues related to health hazards, there is a substantial body of work in progress on the importance of bioaerosols as ice nuclei (IN) and cloud condensation nuclei (CCN), incorporating them into the alteration of cloud coverage and hence, global climate. Until a few years ago, we had no particular interest in this domain, but by accident we discovered that bioaerosols are capable of rapid and efficient transformation of organic matter in snow, and possibly in conditions such as in fogs and clouds. In addition to their IN and CCN capability, we provided an original hypothesis, based on our laboratory and field data, on the potential role of bioaerosols; in altering the chemistry of the atmosphere via microbiological degradation in modifying the chemical composition of other organic compounds upon collision or contact, and hence inducing changes in the IN or CCN ability of organics in the atmosphere, and in driving the chemistry (including photochemistry) at environmental interfaces such as the air/snow interface. However, we would like to emphasize that there are more questions than answers regarding the significance (or lack thereof) that bioaerosol physics and chemistry have on climate change, and we have yet to discover many facets of this amazing multidisciplinary domain. Our ongoing and near future laboratory endeavors include ice nucleation studies of bioaerosols in water/snow, on organic aerosols and attached to sulfate and dust particles; the changes of ice nucleation temperature of organic compounds due to biomaterials, the impact of bioaerosols in the snow and production of volatile organic matter upon or in absence of photolysis, and (iv) the impact of biomaterials in triggering ice nucleation and in cloud formation.
Ice nucleation tests on bacteria isolated from snow as well as grown in the lab, in comparison with those of known organic and inorganic aerosols, shed light on the importance of bio-aerosols on cloud processes. Among many snow bacterial isolates in sampling sites from 43-82 N latitudes, several bacterial species, none belonging to Pseudomonas or Erwinia genera, were identified to show an intermediate range of ice nucleation activity. Comparable results were also obtained for molten snow samples and inorganic suspensions (kaolin and montmorillonite) of buffered water solutions. Considering experimental limitations, and drawing from observation in snow samples of a variety of bacterial populations with variable ice nucleation ability, a shift in airborne-species population may significantly alter glaciation processes in clouds.
Modelling study of bioaerosols in cloud formation
One of the unsolved challenges in cloud microphysics is the rapid formation of exceptionally high ice particle concentrations in warm-based cumulus clouds (cloud base temperatures greater than 0oC) (e.g., Koenigh, 1963; Massop, 1968; Hobbs, 1998; Baker, 2001). Ice particle concentrations can increase from < 0.01 L-1 to more than 100 L-1 in 10 minutes at cloud top temperatures warmer than -10o C. The mechanism which produces ice-particle concentrations two or more orders of magnitude greater than typical concentrations of ice nuclei is not well understood and is therefore difficult to represent in global climate models. In collaboration with Professors Leighton and Yau at 黑料不打烊, we have developed a novel 1.5-dimensional non-hydrostatic cumulus cloud model with bin-resolved microphysics that includes bioaerosols. Our hypothesis, based on some preliminary modelling results, is that ice multiplication in warm-based convective clouds can in fact be explained by the Hallett-Mossop mechanism (an experimentally driven ice multiplication process describing the collisions of grauples with cloud nuclei). If the most active ice nuclei, such as bioaerosols, especially bacteria act as trigger for this process, the issue of ice multiplication can indeed be regarded as issues of warm-rain initiation and ice nucleation. The large ice crystal concentrations generated in the present simulation are not necessarily limited to cumulus clouds but may also occur in large scale stratiform clouds in which supercooled drizzle drops form as a result of some small-scale convection within them. Cloud optical properties and hence shortwave cloud forcing can thus be influenced by the size distribution and phase of the water. This potential forcing is expected to be non-negligible but yet to be evaluated. If the drizzle-sized supercooled drops and bioaerosol ice nuclei in cloud form will be important, they will influence significantly cloud radiative forcing. Parameterization of these two factors in global climate models will benefit the accurate estimation of climate change. Our results will potentially allow global climate models to provide more adequate simulation of the Earth's radiation budget.
Selected related publications in this domain
- P. A. Ariya,A,B F. Domine,C G. Kos,B,H M. Amyot,D V. Cote,B H. Vali,E T. Lauzier,C W. F. Kuhs,F K. Techmer,F T. HeinrichsG and R. Mortazavi, Snow 芒鈧�� a photobiochemical exchange platform for volatile and semi-volatile organic compounds with the atmosphere, Environmental Chemistry. (2010)
- Sun, J., P. A. Ariya, H. G. Leighton, and M. K. Yau, The Mystery of Ice Multiplication in Warm-based Precipitating Shallow Cumulus Clouds, Geophys. Res.Lett. (2010)
- P.A. Ariya, J. Sun, N.A. Eltouny, E.D. Hudson, C.T. Hayes and Kos,G 'Physical and chemical characterization of bioaerosols - Implications for nucleation processes', International Reviews in Physical Chemistry. (2009)
- V. Cote, G. Kos, R. Mortazavi and P. A. Ariya, "Microbial and "de novo" transformation of dicarboxylic acids by three airborne fungi", Science of the Total Environment. (2008)
- R. Mortazavi,C.T. Hayes, P.A. Ariya, "Ice nucleation activity of bacteria from snow compared with organic & inorganic substrates", Environmental Chemistry. (2008)
- P.A. Ariya and M. Amyot, "Bioaerosols: Impact on physics and chemistry of the atmosphere", Atmospheric Environment. (2004)
- P. A. Ariya, O. Nepotchatykh, O. Igntova and M. Amyot, "Microbiological degradation of organic compounds in the atmosphere", Geophysical Research Letters. (2002)