Sunday, February 25, 2007

Chemistry of Atmospheric Aerosols

In recent years, the role of atmospheric aerosols is being increasingly recognized both in climate system of Earth and in global biogeochemical cycle. Aerosols affect the radiative balance of the Earth directly by scattering or absorbing incoming shortwave radiation and indirectly by acting as cloud condensation nuclei, altering a temperature effect at the surface because of changes in cloud cover. In addition, aerosol particles are closely coupled to atmospheric chemistry as chemical reactions in the atmosphere are often accelerated on aerosol surfaces. Also, the chemistry of aerosols may alter their physical and optical properties such as size distribution (fine to coarse) due to interaction between acidic (sulpahte, nitrate) and alkaline (mineral dust) aerosols; single scattering albedo (because of coating of one type of aerosols over other); and surface properties (hydrophilic/hydrophobic), and thus, their direct and indirect effects on climate change. Long range transport and deposition of atmospheric aerosols facilitate the export of nutrients (such as nitrate, phosphate and iron) to and across the oceans which is major source of nutrients as well as limiting factor for primary productivity (or phytoplankton growth) in remote oceans. These phytoplanktons produce biogenic sulfate (via dimethylsulhide), which is the major source of sulfate aerosols over remote oceans.
Also, aerosols are integral part of air pollution and to diagnose and cure the diseases caused by aerosols, the knowledge of their chemical composition is essential. Thus, in order to better understand the effects of aerosols on climate and human health, their physical and chemical properties shall be studied together. For more insight, please see following references:
Andreae, M. O., and P. J. Crutzen (1997), Atmospheric aerosols: Biogeochemical sources and role in atmospheric chemistry, Science, 276, 1052– 1058.
Dentener, F. J., G. R. Carmichael, Y. Zhang, J. Lelieveld, and P. J. Crutzen (1996), Role of mineral aerosol as a reactive surface in the global troposphere, J. Geophys. Res., 101, 22,869–22,889.
Jordan, C. E., J. E. Dibb, B. E. Anderson, and H. E. Fuelberg (2003), Uptake of nitrate and sulfate on dust aerosols during TRACE-P, J. Geophys. Res., 108(D21), 8817, doi:10.1029/2002JD003101.
Rastogi, N., and M. M. Sarin (2006), Chemistry of aerosols over a semi-arid region: Evidence for acid neutralization by mineral dust, Geophys. Res. Lett., 33, L23815, doi:10.1029/2006GL027708.
Tabazadeh, A., M. Z. Jacobson, H. B. Singh, O. B. Toon, J. S. Lin, R. B. Chatfield, A. N. Thakur, T. W. Talbot, and J. E. Dibb (1998), Nitric acid scavenging by mineral and biomass burning aerosols, Geophys. Res. Lett., 25, 4185–4188.
Zhuang, H., C. K. Chan, M. Fang, and A. S. Wexler (1999), Formation of nitrate and non-sea-salt sulfate on coarse particles, Atmos. Environ., 33, 4223– 4233.

1 comment:

pawan said...

Good One