1. Aerosols: Impacts and Policy
Kyla Drushka - 17 November, 2006

2. Health effects of aerosols
Short- and long-term exposure to fine particulate air pollution increases the risk of lung cancer and chronic lung disease, as well as coronary heart disease, pneumonia, and other cancers.1
Particulate matter with a diameter of less than 10 microns is the most damaging air pollutant in terms of health.2
In developed countries, industry and automobile pollution are the primary causes of aerosols, and those who work outdoors face the highest risks; in the developing world, urban air pollution and indoor coal/biomass fires present the greatest risks.
1. Pope, 2002.
2. World Bank, 1997.

3. Health effects of aerosols: China
From Sinton et al., 2004.

4. Health effects of aerosols: China
Indoor coal/biomass burning for cooking and heating is a common practice in developing countries.
Small-scale, inexpensive stoves do not burn fuels cleanly and emit many pollutants and fine aerosol particles; there is disproportionate exposure for women and children.1
Sandstorms, an increasing problem due to desertification and overuse of land, also contribute to harmful aerosols.
Air pollution in China is blamed for >400,000 deaths a year and health damages from air pollution are valued at up to 5% of China's GDP.2
In developing countries, indoor air pollution is the most lethal killer after malnutrition, unsafe sex and lack of safe water and sanitation.1
1. World Health Organization, 2005.
2. World Bank, 1997.

5. Policy to address health effects: China
Pilot programs to give rural Chinese efficient stoves have been met with success: households with improved stoves are negatively correlated with respiratory disease.1
China's most recent five-year plan for the economy devotes ~1.3% of the GDP to its environmental goals.
According to the Chinese government, coal use has decreased from 76% in to 67% in but unless alternatives are developed quickly, China's rapid industrial growth will force coal use to increase again.
China has launched a well-funded research program to evaluate the origin and impact of intense dust storms that plague the country. They have also relocated some farmers in order to try to combat desertification.
1. Sinton et al., 2004.

6. Policy to address aerosol effects: USA
The 1987 PM10 standards decreased the atmospheric concentration of aerosols.
From 1950 to 1990, average surface solar radiation decreased; from 1985 to 2000, it increased.1
Implications: cleaner air is good for our health, but increases the effects of global warming.
1. Wild et al., 2004.

7. Impact of new clean-air policies
Pre-1990
Increase = 8
Decrease = 24
Post-1990
Increase = 26
Decrease = 6
More effective clean air regulations
Political transition in Eastern Europe
Recently, recovery from Pinatubo
1. Wild et al., 2004.

8. Spin-down of the hydrological cycle?1
“Indirect effect” feedbacks:
Increase in droplet concentration...
cooling due to incr. in reflected radiation
decrease in drop size
decrease in precip.
increase in cloudiness, residence time
dry conditions = more dust/smoke
increase in reflection of solar radiation
A decrease in surface solar radiation could cause a decrease in evaporation and thus precipitation, leading to a spin-down of the hydrological cycle.
Annual mean aerosol optical depth (AOD) estimated by a four-dimensional assimilation model that uses satellite- derived AOD for the oceans to constrain the model AODs. The AOD here represents the sum of natural and anthropogenic aerosol.
1. Ramanathan et al., 2001.

9. Changing rain patterns1
In China and India, there has been moderate cooling in recent decades, compared to warming in most of the rest of the world. There has also been increased summer floods in Southern China and droughts in Northern China.
Menon et al. (2002) ran a climate model to evaluate possible aerosol contributions to these trends.
Results: Absorbing aerosols, especially black carbon, can affect regional climate, and the flood/drought trends may be related to an increase in aerosols.
1. Menon et al., 2002.

10. Can aerosols help reduce global warming?1
The warming effects of CO2 could be mitigated by injecting SO2 into the stratosphere.
Example: eruption of Mt. Pinatubo in 1991 injected ~10Tg of S into the stratosphere; the next year saw an average global T decrease of ~0.5°C
Why the stratosphere? Because it is highly stratified, sub-micrometer particles have a long (1-2 year) residence time, compared to particles in the troposphere.
How? (balloons?) How much? (1-2 Tg/year) How much would it cost? ($ billion/year) How much would it help? What might the side-effects be? (ozone degradation, whitening of the sky, ??????)
Crutzen stresses that this would be a last resort, should future attempts to reduce GHG prove as ineffective as current attempts - but it would be effective quickly (within ~6 months)
1. Crutzen, 2006.

11. Conclusions
Cooling due to aerosols is a short-term effect due to the short residence time of aerosols.
Warming due to GHG is long-term because of their long residence time (cumulative effect).
The reduction of aerosols through clean air policy may result in a global temperature increase higher than predicted.

12. References
Menon et al. (2002), Climate effects of black carbon aerosols in China and India, Science, 297(5590),
Pope III, (2002), Lung cancer, cardiopulmonary mortality, and long-term exposure to fine particulate air pollution, JAMA 287(9),
Ramanathan et al. (2001), Aerosols, climate, and the hydrological cycle, Science, 294(5549),
Sinton et al. (2004), An assessment of programs to promote improved household stoves in China, Energy for Sustainable Development 8(3),
Smith (2005), Indoor air pollution: Update on the impacts of household solid fuels, in Environment Matters, The World Bank Group, Annual Review July 2004– June 2005.
Wild et al. (2004), From dimming to brightening: decadal changes in solar radiation at Earth’s surface, Science 308, May 6.
World Bank (1997), Clear Water, Blue Skies: China’s Environment in the New Century, Washington DC: World Bank.
World Health Organization (2005), Indoor air pollution and health. Accessed online 11/15/2006,