Air Pollution, Aerosols and Clouds in the Climate System

The Inter-governmental Panel on Climate Change reviews the best available scientific information on climate change and publishes a report every 5-6 years. The fourth assesment report was released this year and is the IPCC 2007 report. In contrast to the IPCC 2001 report, this report emphasizes with greater confidence that global warming is due to human/anthropogenic activities. Until recently, the sign of the anthropogenic radiative forcing was uncertain largely due to the uncertainty associated with radiative effects (direct and indirect) of atmospheric aerosols. Haywood and Schulz in their recent paper (titled above) inter-compare the probability distribution function of anthropogenic radiative forcing from IPCC 2001 and IPCC 2007 and show that a significant progress has been made in reducing the uncertainty in anthropogenic radiative forcing since IPCC 2001. They conclude that " the single most contributor to this conclusion appears to be the reduction in the uncertainty associ...

It is widely know that dust is essentially non-spherical and hence radiative transfer calculations treating dust as a spherical particle are not adequate. A recent laboratory based study on dust particles by Jingmin Li and Kazuo Osada is very interesting. This article appeared in GRL this month. They study the preferential setting of elongated mineral dust collected from snow in a high mountain in Japan. The positions of particles' centers of gravity and folding centers are analyzed using a scanning electron microscopy and optical microscopy. Their results suggest that a preferential orientation exists for particles settling heavy side down (as expected) but what is interesting is the analysis of results from Ginoux's model wherein they apply this preferential orientation information and show that : " away from the source regions, dust particles are essentially spherical, which considerably simplify the calculation of settling velocity in transport and of radiative trans...

From my graduate school experience I find that the best way to learn and understand science is by getting your hands dirty with the relavant data when it comes to understanding remote sensing. Like remote sensing courses at many other universities in the United States, the University of Alabama in Huntsville offers two courses in Satellite Remote Sensing, ATS670 and ATS770 . These courses are tailored in a manner to that allows students to get hands on experience with state-of-the art remote sensing datasets such as the MODIS . In ATS670, students select a MODIS image of their interest and perform a supervised and unsupervisd classification of the image to identify different features in the image such as land, water, clouds, aerosols, vegetation etc. The beauty of doing all this is that the student doesn't get to use any classification software! They write their own routines to perform all the required tasks including trivial tasks such as calculating minimum, maximum, mean, stand...

Its time for aerosol scientists to gear up for the upcoming Glory Mission that has a fantastic passive sensor for monitoring aerosols from space with unmatched retrieval accuracies of 0.02 over ocean and 0.04 over land! This article on the Glory Mission appeared in BAMS in the May 2007 edition, volume 88, number 5. It has a very detailed description of the science objectives, the instruments on Glory, measurement objectives, the data products from these instruments, associated uncertainties and validation plans. Glory is basically a part of the A-Train constellation of satellites. It is scheduled to be launched in 2008 and will carry two independent instruments : 1) The Total Irradiance Monitor (TIM) 2) The Aerosol Polarimetry Sensor (APS) The main purpose of the Glory mission is to help address the challenge of reducing uncertainty in adequately contraining climate sensitivity. Glory is intented to specifically meet the following four scientific objectives : " • improve the quant...

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 ...

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...

I ran into this article a while ago on EOS transactions (Vol 88, Number 11, 13 March 2007) and it made me pause and think on the message in the article. I thought it was something worth paying attention to and hence decided to post it here for us to contribute to the thought. The purpose of the article was to inform the scientific community of the popularity of Wikipedia and to urge the experts in the community to take a look at the Wikipedia entry for one's area of expertise. The author raises concerns because of the fact that Wikipedia articles are encyclopedic by nature and so provide students with an apparently complete source of material for use in reports and research projects. The question then is: "how good is Wikipedia" in terms of completeness and accuracy? Are students learning the right things? To make Wikipedia as current and updated as possible in terms of information, it allows Anyone with internet connection to write an article about any topic or edit any ...

Global dimming is a term coined for reduction in surface reaching solar radiation. Surface observation of solar radiation over different location around the world shows overall decline in the surface reaching solar energy over long period of time. One of the major causes for this dimming is increase in aerosols loading in the atmosphere. There was research study by Alper et al., 2005 published in GRL. The abstract reads... ‘From the 1950s to the 1980s, a significant decrease of surface solar radiation has been observed at different locations throughout the world. Here we show that this phenomenon, widely termed global dimming, is dominated by the large urban sites. The global-scale analysis of year-to-year variations of solar radiation fluxes shows a decline of 0.41 W/m2/yr for highly populated sites compared to only 0.16 W/m2/yr for sparsely populated sites ( less than 0.1 million). Since most of the globe has sparse population, this suggests that solar dimming is of local or regio...