Introduction

Research objectives | Effects on the Environment | How measurements are made | Measurement-based Assessments

Aerosol effects on the Environment

    Aerosol, smoke and regional pollution fine particles suspended in the air, desert dust and sea salt spray, have a life time of only a few days in the atmosphere. Yet these particles are linked to major environmental effects: weather modification by affecting precipitation patterns and temperature profiles, climate change by competing with regional effects of greenhouse warming, health hazards from air pollution and more.

Forcing of climate:

Aerosols cool the Earth surface by reflecting sunlight to space and by forcing changes in cloud microphysics that consequently increase cloud reflection of sunlight. Aerosol cooling effects have been used to explain why observed global warming over the last century is only 0.6°C rather than the predicted 1°C based on models with no aerosol. On the other hand, black carbon, defined as the light absorbing components of carbonaceous material, e.g. the dark organic and inorganic carbon left over from incomplete combustion, is warming the atmosphere along with greenhouse gases. Including the warming effects of black carbon aerosols can explain why global warming took place in the last century at all despite the strong aerosol cooling. Therefore understanding of the aerosol effects on the Earth radiation budget is critical to explain past and future climates.

Weather and agriculture:

In regions with heavy pollution or biomass burning, aerosols were recently found to affect precipitation via several possible pathways:

- In the Indian subcontinent a recent study using TRMM data suggests that precipitation over the sub continent is being reduced by the fine pollution aerosol and the moisture is released later as rain over the ocean, due to interaction with coarse particles - sea salt [Rosenfeld, 2002].

- Over China the strong absorption of sunlight by black carbon emitted from incomplete consumption of fossil fuel, and the consequent cooling of the surface and warming of the atmosphere is modeled to explain the droughts in Northern China and the floods in Southern China. The hot air, heated by the black carbon absorption rises, advects moisture from the ocean, thus changing the global air circulation and enhancing regional precipitation [Menon et al., 2002].

- Over the Mediterranean region, warming of the atmosphere and cooling of the surface by the black carbon in smoke and urban haze advected south from Eastern Europe, France and Germany is modeled to reduce evaporation and consequently precipitation by 10-50% in this already water thirsty zone [Lelieveld et al., 2002].

- Future climates in the next 50 years are expected to be strongly affected by aerosol emissions, which may increase or decrease by as much as 50% the expected global warming due to greenhouse gases, depending on their black carbon content [Hansen et al., 2000].

- Population growth and increase in economic production is expected to drive up emissions of aerosol. The fraction of black carbon in the aerosol depends on emission regulations and technology developments, and therefore may be influenced by policy and technological standards.

Fertilization of the Oceans:

Dust is a major source of iron fertilization of the ocean. The concentration of iron oxides that are source of nutrition to oceanic phytoplankton is proportional to the dust absorption of sunlight, and plays a role as a feedback in climate change [Gao et al., 2001].

Human health:

It is suspected that 1-4% of deaths worldwide are associated with air pollution. Combination of passive and lidar satellite instrument can monitor air pollution aerosol distribution. The data fed into assimilation models can be used to predict aerosol air quality in a similar way to prediction of ozone today [Greenbaum, 2002].

Research objectives | Effects on the Environment | How measurements are made | Measurement-based Assessments

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