Friday, July 20, 2007

Levoglucosan: a unique tracer of biomass burning aerosols

Atmospheric aerosols in general and biomass burning aerosols in particular have recently attracted extensive interest owing to their ability to affect the climate on local to global scales. These climatic effects include a direct radiative effect due to the aerosols’ ability to scatter and absorb incoming sunlight, an indirect effect due to the aerosols’ ability to serve as cloud condensation nuclei (CCN), increasing the cloud’s reflectivity and lifetime, a semidirect effect which leads to reduction in cloud cover, owing to aerosols’ ability to absorb sunlight, changes in precipitation patterns, and export of pollutants and water vapor to the stratosphere. Therefore, it is important to assess human contribution to aerosol emissions, and to assign a source to both anthropogenic and natural aerosols, for understanding the respective contribution of different aerosol types to climate change.

Levoglucosan (1,6-anhydro-β-D-glucopyranose) is a unique tracer for biomass burning sources in atmospheric aerosol particles. It is a product of cellulose combustion, which has been recognized as a biomass burning tracer. When cellulose is heated to over 300°C, it undergoes various pyrolytic processes, yielding a highly combustible tar, a major constituent of which is levoglucosan, a dehydrated glucose containing a ketal functional group. Some of the levoglucosan is consumed in various reactions during combustion but it is nonetheless emitted in large quantities in the resulting smoke aerosol. Therefore, it can be utilize as a specific tracer for the presence of emissions from a biomass burning source in atmospheric particulate matter. Unlike other indicators used for the same purpose, levoglucosan is source-specific to burning of any fuel containing cellulose. Combustion of other materials (e.g., fossil fuels) or biodegradation and hydrolysis of cellulose do not produce levoglucosan. Levoglucosan is relatively stable in the atmosphere, showing no decay over 10 days in acidic conditions, similar to those of atmospheric liquid droplets. Levoglucosan is also used in other fields of chemistry and engineering, such as pyrolysis and fire-retardants research, biofuel research, biology, organic synthesis and as a biomass burning tracer in sediment analysis for the paleorecord.
For more information, please see the following paper and references therein.

Schkolnik G. and Rudich Y. (2006), Detection and quantification of levoglucosan in atmospheric aerosols: A review, Analytical and Bioanalytical Chemistry, 385, 26-33.

2 comments:

Harish Gadhavi said...

Neeraj,
How one measures levoglucosan? What amount it is produced say in proportion to black carbon during bio-mass burning?

Harish

Neeraj Rastogi said...

Hi Harish,

Good question,

I have written the importance/motive of measuring Levoglucosan. It can be measured by different ways such as Liquid Chromatography, Gas Chromatography and NMR. This choice depends upon the suite of other chemical species in which researcher is interested. The details of measurments and other characteristics are given in the reference paper.

Neeraj