Fractal aircraft trajectories and nonclassical turbulent exponents.

The dimension (D) of aircraft trajectories is fundamental in interpreting airborne data. To estimate D, we studied data from 18 trajectories of stratospheric aircraft flights 1600 km long taken during a "Mach cruise" (near constant Mach number) autopilot flight mode of the ER-2 research aircraft. Mach cruise implies correlated temperature and wind fluctuations so that DeltaZ approximately Deltax (H(z) ) where Z is the (fluctuating) vertical and x the horizontal coordinate of the aircraft. Over the range approximately 3-300 km , we found H(z) approximately 0.58+/-0.02 close to the theoretical 5/9=0.56 and implying D=1+ H(z) =14/9 , i.e., the trajectories are fractal. For distances <3 km aircraft inertia smooths the trajectories, for distances >300 km , D=1 again because of a rise of 1 m/km due to fuel consumption. In the fractal regime, the horizontal velocity and temperature exponents are close to the nonclassical value 1/2 (rather than 1/3 ). We discuss implications for aircraft measurements as well as for the structure of the atmosphere.

Organic aerosols and the origin of life: an hypothesis.

Recent experimental work has verified the prediction that marine aerosols could have an exterior film of amphiphiles; palmitic, stearic and oleic acids were predominant. Thermodynamic analysis has revealed that such aerosols are energetically capable of asymmetric division. In a prebiotic terrestrial environment, one of the products of such aerosol fission would have been bacterially sized (microns), the other would have been virally sized (tens of nanometers). Plausible avenues for chemical differentiation between the two particles are discussed, and the probabilities for the transition from geochemistry to biochemistry updated in light of recent palaeo fossil studies.

The asymmetry of organic aerosol fission and prebiotic chemistry.

We examine the prebiotic applicability of our recent analysis of the fission of an atmospheric aerosol particle coated with an organic film. The fission is made possible by the free energy change upon compression of the exterior monolayer film on the parent particle, which overcomes the increase in surface area associated with the production of two spherical daughter particles. Asymmetric division into a larger and a smaller particle becomes possible following surfactant film collapse. The size of the airborne parent particle is determined by the balance between aerodynamics and gravity, while the ratio of the radii of the daughters is determined by the compression characteristics of the amphiphilic molecules comprising the parent film. For an Earth atmosphere of one bar surface pressure, the larger and smaller daughters have the sizes of a single-celled bacterium and of a virus respectively. Chemical differentiation between the daughters is possible.

Atmospheric aerosols as prebiotic chemical reactors.

Aerosol particles in the atmosphere have recently been found to contain a large number of chemical elements and a high content of organic material. The latter property is explicable by an inverted micelle model. The aerosol sizes with significant atmospheric lifetimes are the same as those of single-celled organisms, and they are predicted by the interplay of aerodynamic drag, surface tension, and gravity. We propose that large populations of such aerosols could have afforded an environment, by means of their ability to concentrate molecules in a wide variety of physical conditions, for key chemical transformations in the prebiotic world. We also suggest that aerosols could have been precursors to life, since it is generally agreed that the common ancestor of terrestrial life was a single-celled organism. The early steps in some of these initial transformations should be accessible to experimental investigation.

Instrumental requirements for global atmospheric chemistry.

The field of atmospheric chemistry is data-limited, primarily because of the challenge of measuring the key chemical constituents in the global environment. Several recent advances, however, in rugged, portable, remotesensing, ground-based instrumentation and accurate, fast-response airborne instrumentation have provided powerful tools for the understanding of stratospheric ozone, particularly in polar regions. Current discoveries of the role of heterogeneous chemical processes point to the need for better techniques for characterization of stratospheric aerosols. In the troposphere, advances in in situ, sensitive methods for detecting reactive nitrogen compounds have demonstrated the role that these compounds have in controlling global oxidation processes, but better measurements of the reservoir species by which the long-ranged transport of pollutant-reactive nitrogen compounds is thought to occur are urgently needed. The role of hydrocarbons, particularly those of natural origin, in ozone formation in rural areas has focused attention on the requirement for better speciation of these ubiquitous compounds. Lastly, rigorous instrument intercomparison experiments have provided unbiased estimates of measurement capabilities.