Effects of atmospheric aerosolsAtmospheric aerosol particles play important role in radiation budget of the Earth’s as they scatter and absorb both shortwave solar radiation and longwave terrestrial radiation. They are also highly involved in the formation of clouds and precipitation since they operate as cloud condensation and ice nuclei (CCN and IN). Aerosols can form the abundance and distribution of atmospheric trace gases by complex chemical reactions, and can affect significantly the cycles of nitrogen, sulphur, and atmospheric oxidants. Aerosol particles in the upper atmosphere, where the major part of atmospheric ozone forms, can modify the ozone removal (Mészáros, 2000). Additionally, particles are major elements of lower tropospheric air quality, and can influence harmfully the environment and human health.
Aerosols play important role in the balance of the Earth’s climate. Due to the increasing anthropogenic emission of aerosols since the industrial revolution, they can also effect the global climate change. However, the effects of aerosols on climate are not one-way, moreover excessively uncertain. The climate forcing by aerosols can be realized in two ways, basically: in direct and indirect radiative forcing.
The properties and the number of particles can affect the formation and the characteristic of clouds and precipitation in many ways (Lohmann and Feichter, 2005). The increased number of aerosol particles, and therefore the increased cloud optical thickness decrease the net surface solar radiation. The more numerous smaller cloud particles reflect more solar radiation (called albedo effect or Twomey effect). Smaller particles decrease the precipitation efficiency, thereby prolonging cloud lifetime. The absorption of solar radiation by soot particles may cause evaporation of cloud particles (semi-direct effect). In mixed-phased clouds, smaller cloud droplets delay the beginning of freezing and decrease the riming efficiency. However, more ice nuclei increase the precipitation efficiency.
Anthropogenic aerosols effects on water clouds through the cloud albedo effect cause a negative radiative forcing of –0.3 to –1.8 W m–2 (IPCC, 2007).