The ABC hotspot regions are those where annual mean anthropogenic aerosol optical depth (AOD) exceeds over 0.3 and where carbon particles make up at least 10% of the clouds. The Aerosol Optical Depth (AOD) is a quantitative measure of the extinction of solar radiation by aerosol scattering and absorption between the point of observation and the top of the atmosphere. It is a measure of the integrated columnar aerosol load and the single most important parameter for evaluating direct radiative forcing. AOD can be determined from the ground through measurements of the spectral transmission of solar radiation through the atmosphere using rather simple and relatively inexpensive instruments pointed directly at the sun called sun-photometers or filter radiometers. Routine ground based AOD observations are of utmost importance for the calibration and validation of AOD retrievals from satellites. In addition they are necessary to correct for aerosol effects in the retrieval of other satellite products.
ABC hotspots region in the world
(Source: United Nations Environment Program)
The major Regional hotspots:
- Indo Gangetic Plain in South Asia (Northwest to northeast region extending from eastern Pakistan, across India to Bangladesh and Myanmar)
- East Asia (Eastern China, Thailand, Vietnam & Cambodia)
- Indonesian Region
- Southern Africa extending southwards from sub-Saharan Africa into Angola, Zambia and Zimbabwe
- The Amazon basin in South America
The Asian continent is the world’s largest living habitat with about 60% of the world’s population. Especially south Asia has been undergoing high transformations in the urban and industry sectors because of the growing population and globalization. The United Nations Environment Program (UNEP) has done a comprehensive study of the South Asian haze and its impact on climate. It is largely based on the studies of the INDOEX (Indian Ocean Experiment) science team of over 200 scientists from Europe, India and USA. It provides a summary of the large brownish haze layer and its impact on the radiative heating of the atmosphere and the surface for South Asia and the adjacent Indian Ocean during the INDOEX campaign. It also discusses preliminaryfindingswith respect to the impact of this haze on regional temperatures, precipitation, agriculture and health.
The INDOEX campaign began in 1995 with ship observations and culminated in a major field campaign launched from the Maldives during January to April of 1999, with ships, aircraft, satellites and surface observations. An aerosol-chemistry-climate observatory was established on an island in the Maldives. The discovery during INDOEX of the so-called South Asian haze is clear evidence of the magnitude of the aerosol pollution problem. Three dimensional aerosol-assimilation models reveal this haze to extend over South, Southeast and East Asia. At present, biomass burning and fossil fuel burning are the major sources of air pollution. Due to lack of observations of emissions at the source regions in South Asia, it was infeasible to determine with confidence the relative contribution of biomass and fossil fuel burning to the observed haze. But tentative conclusion is that biomass burning plays a major role in gaseous pollution (such as carbon monoxide), while fossil fuel combustion and biomass burning contribute to particulate (aerosol) pollution. The affected region is the most densely populated in the world characterized by a monsoon climate, high levels of pollution, and increasing problems of water stress, agricultural productivity and health.
The synoptic view of the Asian during INDOEX, top left, from the SEAWiFS satellite. The three photographs on the right taken from the C-130 research aircraft show images of (a) the dense haze in the Arabian Sea, (b) the trade cumuli (a type of cloud) embedded in the haze and (c) the pristine southern Indian Ocean. (Courtesy of N. Kuring, NASA Goddard Space Flight Center)
- A recent UNEP report identified Mumbai, Delhi, and Kolkata as being among 13 ABC hotspots in the Asian region.
- From the year 2001 to 2005 Aerosol Optical Depth (AOD) over Panaji went from 0.39 to 0.41 and over Bhopal from 0.40 to 0.42
- A paper published by S Ramchandran, of the Physical Research Laboratory, Ahmedabad in the geophysical research journal points to an increasing number of aerosols hanging over Indian cities, with Kolkata having the highest count in 2005 with a 0.59 AOD count. Delhi was next with 0.57, followed by Chennai (0.47), Mumbai (0.41) and Bangalore (0.32).
- The highest black carbon emissions in four Indian metros Chennai, Kolkata, Mumbai and Delhi came from diesel combustion in the transport sector.
- A study conducted by Chandra Venkataraman, professor from the department of chemical engineering, Indian Institute of Technology, Mumbai observes that coal combustion in thermal power plants and fossil fuels used in the transportation and industrial sectors were found to contribute most of the aerosol pollutant emissions over India.
- The highest aerosol emissions of sulphur dioxide from fossil fuels were observed in the states of Tamil Nadu, Maharashtra, Utter Pradesh, Gujarat and West Bengal due to thermal power plants and large number of point sources (refineries, petrochemicals cement and fertilizers) in these states.
- Delhi often complains of fog or fog like conditions. This is because, the Pollutants remain suspended in the air due to the absence of any sink like ocean.
- Mumbai had AOD of 0.44 in 2003, but fell again to 0.41 in 2005. In coastal cities like Mumbai breezes blow pollutants towards the ocean, where they settle on water, never to rise again. This results in the lower level of AOD in the atmosphere.
- Indian Institute of Tropical Meteorology, Pune has been measuring AOD on a daily basis since 20 years and recently concluded that aerosol levels over Pune have increased by 14% as compared to past two decades.