Levy, R.C., and R.T. Pinker, 2007: Remote Sensing of Spectral Aerosol Properties: A Classroom Experience, Bull. Amer. Meteor. Soc., 88, 25–30
Welcome to the world of atmospheric aerosols, clouds and climate science. Atmospheric aerosols (or PM) are complex mixture of solid and liquid particles that vary in size and composition, and remain suspended in the air. They affect human health and play an important role in weather and climate change processes. Due to high temporal and spatial variability, their characterization into climate models is highly uncertain. This blog is our science diary about latest research in this field.
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.
Ultraviolet (UV) radiation plays very important role in bio-geo-chemical cycle. Their harmful effects include skin cancer, cataract, immune suppression, reduction in crop yield, etc. Beneficial effects are synthesis of vitamin D in human body, treatment of psoriasis, etc (Lucas et al., 2006). My interest in UV radiation is how it interacts with atmospheric aerosols.
Aerosols are one of the many factors which determines amount of surface reaching UV radiation. While scattering type of aerosols may reduce surface reaching UV radiation, they increase the actinic flux which in turn increases the photolysis rate for smog formation (Dickerson et al., 1997). Relation of aerosol and UV radiation is not one-way; while aerosols affect surface reaching UV radiation, they are affected by surface reaching UV radiation. This is particularly true for naturally produced sulfate aerosol. Recently scientific community has shown a lot of interest to study UV induced sulfate aerosol production to better understand effect solar variability on climate change. Joyce Penner presented a talk on connection between Solar variability, Dimethyl sulfide (DMS) production, and climate change in Yoram Kaufman Symposium on Aerosols, Clouds and Climate (30-31 May 2007). The symposium was organized in honor of Yoram Kaufman at Goddard Space Flight Center, NASA, Maryland, USA. Presentations are available for download at this link.
Penner presented the details on solar variability and DMS production and showed how the matter is complicated due to cloud feedback. The connection works as following; increase in ultraviolet radiation decreases the marine biota, which in turn reduces production of DMS . Reduction in DMS reduces aerosol amount, which ultimately leads to cloud modification. The poorly understood connections between aerosol and cloud as well as cloud and marine biota makes it difficult to interpret solar variability connection of climate change. Two references cited repeatedly in her talk were Larsen (2005) and Vallina and Simo (2007).
Lucas, R., T. McMichael, W. Smith. and B. Armstrong (2006), Global burden of disease from solar ultraviolet radiation, Environmental burden of diseases series no. 13, ed. A. Pruss-Ustun, H. Zeeb, C. Mathers and M. Repacholi, World Health Organization Public Health and the Environment, Geneva, 2006.
R. R. Dickerson, S. Kondragunta, G. Stenchikov, K. L. Civerolo, B. G. Doddridge, and B. N. Holben, The Impact of Aerosols on Solar Ultraviolet Radiation and Photochemical Smog , Science 31 October 1997 278: 827-830 [DOI: 10.1126/science.278.5339.827]
Larsen, S. H. (2005), Solar variability, dimethyl sulphide, clouds, and climate, Global Biogeochem. Cycles, 19, GB1014, doi:10.1029/2004GB002333.
Vallina, S. M. and R. Simo (2007), Strong Relationship Between DMS and the Solar Radiation Dose over the Global Surface Ocean, Science, Vol. 315, No. 5811. pp. 506-508