Air Pollution, Aerosols and Clouds in the Climate System

It has been long time since passive satellite observations in visible and thermal part of the spectrum have been used to monitor and quantify the biomass burning over global areas. Space sensors such as AVHRR, MODIS, and GOES are some of the examples, which continuously monitor vegetation fires under clear sky conditions. But, these sensors are limited to cloud free conditions and there could be large errors in estimation of fire activities due to lack of sampling under cloudy conditions. Remote Sensing of Environment published a research article entitled “ Quantifying the impact of cloud obscuration on remote sensing of active fires in the Brazilian Amazon ” by Wilfrid Schroeder and coauthors discuss the bias in remote sensing fire data due to possible cloud cover during fire activities over Brazilian Amazon. The abstract read as “Vegetation fires remain as one of the most important processes governing land use and land cover change in tropical areas. The large area extent of fire pr...

MODIS aerosol optical thickness (AOT) retrieval algorithm over land is continuously improving and now operational to produce collection 5 aerosol data products. Both Terra and Aqua data has been reprocessed using new retrieval algorithm. Click here to view current data processing status. New algorithm replaced the surface reflectance assumptions, the set of aerosol model optical properties, and the aerosol lookup table to reduce uncertainty in the product. In collection 5 retrievals of small-magnitude negative AOT values (down to −0.05) are considered valid, thus balancing the long term statistics of τ in near zero AOT conditions. Initial validation exercise conducted on this algorithm shows much improved retrievals of AOT. As consequence, global mean AOT for the test bed is reduced from ∼0.28 to ∼0.21. Last month two research articles published in JGR-Atmosphere discussing new algorithm: Levy R. C., L. A. Remer, S. Mattoo, E. F. Vermote, Y. J. Kaufman (2007), Second-generation opera...

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 betw...

In the recent decade aerosols have gained much attention from a climate perspective. Researchers have been using both observations and modeling studies to address the question on radiative effects of aerosols and their role in global climate change. Ground based observations have provided unmatched understanding of aerosol optical and microphysical properties. Sophisticated remote sensing instruments such as MODIS, MISR, OMI, TOMS onboard various satellite platforms provide routine measurement of aerosol loading over the entire globe. While much attention was being paid on characterizing aerosols and understanding their radiative effects not much speculation was done over their concentration trends over past decade or so until recently. An interesting paper appeared in Science on March 16, 2007 by Michael Mishchenko et al on “Long-Term Satellite Record Reveals Likely Recent Aerosol Trend “. They analyzed the Global Aerosol Climatology Project (GACP) data set to show a decrease in g...

This paper by Dubovik et al., appeared online in Atmos. Chem. Phys. Discuss. The abstract read as "Knowledge of the global distribution of tropospheric aerosols is important for studying the effects of aerosols on global climate. Chemical transport models rely on archived meteorological fields, accounting for aerosol sources, transport and removal processes can simulate the global distribution of atmospheric aerosols. However, the accuracy of global aerosol modeling is limited. Uncertainty in location and strength of aerosol emission sources is a major factor in limiting modeling accuracy. This paper describes an effort to develop an algorithm for retrieving global sources of aerosol from satellite observations by inverting the GOCART aerosol transport model. To optimize inversion algorithm performance, the inversion was formulated as a generalized multi-term least-squares-type fitting. This concept uses the principles of statistical optimization and unites diverse retrieval techn...

NASA launched its first Earth Observing System satellite Terra in May 1999 with five different sensors onboard to monitor and study earth-atmosphere system. MISR is one of the instruments, which is primarily designed to study aerosols and clouds. More on MISR instrument is given in previous post by Harish in the same blog. Since the launch, MISR is providing good quality data of various aerosol properties over global ocean and land. Multi-angle capability of MISR enables retrieval of aerosol properties over both dark and bright targets, which is not available from other sensors such as MODIS . The most important parameter in aerosol research is aerosol optical thickness (AOT), which indirectly tells us columnar loading of aerosols in the earth-atmosphere system. Validation exercise shows that 67% time AOT are within ±0.05 or 20% of AEROENT AOT ( Kahn et al., 2005, Abdou et al., 2005, Christopher and Wang, 2004, Martonchik et al., 2004 and Jiang et al., 2006 ). Also, the accuracies ar...

Multi-angle Imaging SpectroRadiometer (MISR) is an instrument flown aboard terra satellite by NASA on August 1999. As its official web-site truly claims; no instrument like MISR flown before in the space. The unique feature of MISR is its nine cameras looking in nine different directions simultaneously. This affords us to view a given place on the earth from different angles and made it possible to estimate many physical parameters from space. Concept of the MISR is based on a fact that if directional dependence of the scattered light is studied carefully it can reveal many features about target. Sunlight falling on the earth is not scattered equally in all directions. Halos around the moon in the presence of cirrus clouds is one of such phenomena. Ability to view a given location from multiple angle has made it possible to observe many physical quantities for atmospheric aerosols and clouds which otherwise were not possible or difficult to observe from space such as single scattering...

'Wind reduction by aerosol particles' this is the title of Yoram Kaufman's one of the last published paper appeared in GRL during last month. Yoram was well-known scientist in aerosol community and called as 'father of satellite remote sensing of aerosols'. The present paper discusses the new dimension of aerosol research. Several research studies focusing impact of wind speed on aerosols are published but this is first time Jacobson along with Yoram talks about effects of aerosols on wind speed. Study shows that directly and indirectly aerosol particles can reduce wind speed by 8% locally, which is related to reduction in precipitation. Refer the published article for further findings of the research and detailed methodology used. Jacobson, M. Z., and Y. J. Kaufman (2006), Wind reduction by aerosol particles, Geophys. Res. Lett., 33, L24814, doi:10.1029/2006GL027838.