Sources and Impact of ABCs
Various natural sources and anthropogenic activities are responsible for the formation of ABCs. Natural sources involves forest fires, volcanic eruption, desert storms etc., while anthropogenic activities like incomplete combustion of fossil fuels, biomass burning, automobile exhaust, industrial emissions, burning of agricultural waste after harvesting and thermal power plant significantly contribute to the increased levels of ABCs in the atmosphere.
Impact of ABCs:
ABCs causes direct and indirect effects on the environment as well as on the human beings. Direct effects are restricted mainly to the regions beneath the haze layer that involves melting of glaciers, change in weather pattern etc. Indirect effect leads to cooling of the land surface, formation of thermal inversion etc.
- The aerosols in ABC reduce the amount of sunlight reaching the earth’s surface by as much as 10 to 15 %, and enhance atmospheric solar heating by as much as 50 %. Thus, ABCs, on one hand mask the greenhouse warming by the surface dimming; while on the other hand, enhance the greenhouse warming of the atmosphere.
- Aerosols can directly alter the hydrological cycle by suppressing evaporation and rainfall. Decrease in the Indian monsoon rainfall, especially over northern half of India and a north-south shift in rainfall patterns in eastern china has been observed.
- Reduction in the precipitation efficiency by inhibiting the formation of larger size raindrop particles leading to drought like conditions.
- Reduction in agricultural productivity, which involves decrease in the photosynthetic activity due to the deposition of aerosols on the plant leaves. This results in the reduction in crop yields. Deposition of aerosols can also increase acidity and cause plant damage.
- Changes in surface temperature can directly impact the growing season. In the tropics, a surface cooling caused due to aerosols can extend the growing season.
- Elevated levels of ground-level ozone, which could result in reduction in the crop yield of wheat and legumes.
- Glaciers in ranges like Hindu Kush-Himalayan-Tibetan are melting faster and weather systems are becoming more extreme.
- ABCs leads to adverse health effects on human beings. Increase in acute respiratory infections, lung cancer, chronic obstructive pulmonary and cardiovascular diseases is observed in Nepal, India, and China.
- Increase in the frequency and strength of the thermal inversion that can trap more pollutants and enhances the formation of secondary air pollutants.
- Cooling of the land surface due to trapping of the solar radiation in the upper atmospher