Tuesday, June 26, 2007

Radionuclides in Aerosols

7Be and 210Pb are the natural radionuclides present in the atmosphere. Several studies have shown that useful information about transport, removal and residence time of aerosols in the atmosphere can be obtained from the measurements of 7Be and 210Pb. 7Be (half-life = 53.3 days) is produced by cosmic ray spallation of nitrogen and oxygen primarily in lower stratosphere and upper troposphere. Therefore, 7Be is used as a tracer of stratospheric or high tropospheric sources such as ozone, stratospheric bomb fallout debris, stratospherically injected volcanic components. In contrast, 210Pb (half-life = 22.3 years) is a progeny of 238U. The source of 210Pb is radioactive decay of 222Rn (half-life = 3.8 days), a noble gas, continuously emitting from soils to the atmosphere. Thus, 210Pb is a tracer of continental air as more than 99% 222Rn is emanating from the surface of continents. Half-life of both the radionuclides are long enough with respect to their residence time in the lower atmosphere, therefore the principal removal pathway of the 7Be and 210Pb is via dry and wet deposition rather than radioactive decay. Since the sources of 7Be and 210Pb are well established and different in terms of altitude, their simultaneous study provides useful information about the vertical and horizontal mixing of air masses in the atmosphere. For further study, please see the following references and references therein.

Balkanski, Y. J., D. J. Jacob and G. M. Gardner (1993), Transport and residence times of tropospheric aerosols inferred from a global three-dimensional simulation of 210Pb, J. Geophy. Res., 98, 20573–20586.

Graustein, W. C. and K. K. Turekian (1996), 7Be and 210Pb indicate an upper troposphere source for elevated ozone in the summertime subtropical free troposphere of the eastern North Atlantic, Geophys. Res. Lett., 23, 539-542.

Gaffney, J. S., N. A. Marley and M. M. Cunningham (2004), Natural radionuclides in fine aerosols in the Pittsburgh area, Atmos. Environ., 38, 3191-3200.

Lee, H. N., L. Tositti, X. Zheng, and P. Bonasoni (2007), Analyses and comparisons of variations of 7Be, 210Pb, and 7Be/210Pb with ozone observations at two Global Atmosphere Watch stations from high mountains, J. Geophys. Res., 112, D05303, doi:10.1029/2006JD007421.

Tuesday, June 12, 2007

New Dimension to Aerosol Research: CALIPSO the Space LIDAR

NASA in collaboration with CNES, BALL, IPSL and Hampton University launched state-of-art dual channel space LIDAR on April 28, 2006. Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) is flying in constellation of satellites called A-Train along with Aura, PARASOL, CloudSat, Aqua, taking Earth observations within 7-8 minutes and OCO will soon join them to complete the A-Train.

CALIPSO took its first observation (image on right) on July 24, 2006 and last December its level 1 radiance, lidar level 2 vertical feature masks, cloud and aerosol layer products are released to the public. These data sets are unique in various ways and will provide new dimension (vertical) to the aerosol research. CALIPSO provides long awaited global vertical profiles of aerosols in the atmosphere, which will be very useful for air quality, earth radiation budget and climate change studies. An example is shown below: Read More About Image Here
This graphic shows a flight comparison between CALIPSO data (middle) and data taken from the cloud physics lidar on the ER-2 (bottom) from the same time a location on August 12. The image at the top is infrared data from a GOES satellite illustrating the cloud cover that both the CALIPSO and the ER-2 lidars observe. The flight path of the ER-2 and the CALIPSO track can be seen at the right of the image as a solid line

Here in this blog post, I am providing some useful link to CALIPSO and its data sets


Watch great movie of A-train orbits

More about A-train

CALIPSO outreach

CALIPSO Data page

CALIPSO Image browser

Monday, June 4, 2007

Atmospheric radiative effects of an in-situ measured Saharan dust plume and the role of large particles

This interesting paper appeared in ACPD on June 4 and abstract reads :

This work will present aerosol size distributions measured in a Saharan dust plume between 0.9 and 12 km altitude during the ACE-2 campaign 1997. The distributions contain a significant fraction of large particles of diameters from 4 to 30 μm. Radiative transfer calculations have been performed using these data as input. Shortwave, longwave as well as total atmospheric radiative effects (AREs) of the dust plume are investigated over ocean and desert within the scope of sensitivity studies considering varied input parameters like solar zenith angle, scaled total dust optical depth, tropospheric standard aerosol profiles and particle complex refractive index. The results indicate that the large particle fraction has a predominant impact on the optical properties of the dust. A single scattering albedo of ωo=0.75–0.96 at 550 nm was simulated in the entire dust column as well as 0.76 within the Saharan dust layer at ~4 km altitude indicating enhanced absorption. The measured dust leads to cooling over the ocean but warming over the desert due to differences in their spectral surface albedo and surface temperature. The large particles absorb strongly and they contribute at least 20% to the ARE in the dusty atmosphere.

From the measured size distributions modal parameters of a bimodal lognormal column volume size distribution were deduced, resulting in a coarse median diameter of ~9 μm and a column single scattering albedo of 0.78 at 550 nm. A sensitivity study demonstrates that variabilities in the modal parameters can cause completely different AREs and emphasises the warming effect of the large mineral dust particles

Reference :

S. Otto, M. de Reus, T. Trautmann, A. Thomas, M. Wendisch, and S. Borrmann, Atmospheric radiative effects of an in-situ measured Saharan dust plume and the role of large particles, Atmos. Chem. Phys. Discuss., 7, 7767-7817, 2007