THE ATMOSPHERIC BROWN CLOUD.
Is layer of air pollution containing aerosols such as soot or dust that absorb as well as scatter incoming solar radiation, leading to regional and global climatic effects and posing risks to human health and food security.
This layer extends from Earth’s surface to an altitude of roughly 3 km (1.8 miles).
Urban brown clouds are heavily influenced by thermal inversions in the atmosphere and are a widespread, regional phenomena occurring over several cities.
HISTORY
The first observations of these phenomena were made in the late 1990s as part of the Indian Ocean Experiment (INDOEX), in which coordinated air pollution measurements were taken from satellites, aircraft, ships, surface stations, and balloons. This research revealed a large aerosol formation over most of South Asia and the northern Indian Ocean.
OCCURRENCE
This “Asian brown cloud” is an annual phenomenon that occurs primarily from November through May. Data have shown that atmospheric brown clouds are a global phenomenon and are associated with human-generated air pollution from Africa, North America, South America, and Europe, as well as Asia. Atmospheric brown clouds are particularly prevalent in tropical regions; they occur as a result of elevated pollutant emissions and a lengthy dry season that prevents aerosols from being removed from the atmosphere through precipitation.
SOURCE OF POLLUTION
Atmospheric brown clouds are caused by emissions associated with the combustion of fossil fuels and biomass. The brown colour of the clouds results from the absorption and scattering of solar radiation by black carbon, fly ash, soil dust particles, and nitrogen dioxide.
Because of rapid economic development the air pollution has is increasing in a high rate.
DIMMING 6% !
India and China are dimmer at the surface today by at least 6 percent compared with their state in preindustrial times. The presence of two types of aerosols in the air reduces the amount of solar radiation reaching the surface of the Earth
Black carbon and organic carbon
Aerosols in brown clouds are made up primarily of black carbon and organic carbon. These aerosols, especially the black carbon component, absorb solar radiation, and this absorption results in enhanced solar heating of the atmosphere.
Sulfates and nitrates
Other aerosols, such as sulfates and nitrates, scatter solar radiation back to space.
Combined together both aerosols are r
- reducing in the amount of solar radiation reaching the surface
- Causing to lower surface temperatures.
- A lower surface temperature slows the rate of evaporation.
- Which reduces the amount of precipitable water in the atmosphere.
- The resulting declines in precipitation influences the regional hydrological cycle.
For example, atmospheric brown clouds have played a major role in decreases in summer monsoon rainfall in India since 1930. In addition, aerosol pollution has been linked to the southward shift of the summer monsoon in eastern China and to changes in precipitation patterns in other tropical regions.
LESS AGRICULTURAL PRODUCTION
Changes in precipitation and climate due to atmospheric brown clouds can modify regional agricultural production. These impacts are complex and are likely to be different depending on crop types. One study estimated that from 1985 to 1998 Indian rice output was reduced by 6.2 million metric tons (about 6.8 million tons—that is, enough rice to feed 72 million people) because of air pollution related to the Asian brown cloud.
A THREAT TO HUMAN HEALTH
In addition, pollution from atmospheric brown clouds is a threat to human health. Particulate matter, such as soot and dust, has been linked in epidemiological studies to cardiovascular problems, chronic respiratory problems, and mortality. Brown clouds also contain ozone and other hazardous pollutants. Ozone can irritate lung tissue, exacerbate asthma, and reduce lung function.
Ozone has also been linked to reduced crop yields.
CLIMATE CHANGE : THE MAGNITUDE OF THE PROBLEM