ROLES OF TROPOSPHERIC OZONE AND AEROSOLS IN CLIMATE CHANGE
Pennsylvania State University, State College, Pennsylvania
Human activities, such as burning fossil fuels, release into the atmosphere two short-lived pollutants that affect global climate â€“ ozone and aerosol particles. Although ozone plays a crucial role in protecting Earthâ€™s surface from ultraviolet radiation, it is a greenhouse gas produced by industrial processes that stays in the troposphere. Like all greenhouse gases, ozone influences the atmospheric temperature, humidity and winds. Aerosol particles, defined as suspended small particles with widely varying size, affect climate by ...view middle of the document...
This reaction involves the two chemicalsâ€™ photochemical reaction with sunlight. In general, an increase in temperature will increase the rate of this reaction. Discovered by scientists, there is a strong correlation between higher ozone concentrations and warmer days. When there is a higher temperature (such as in summer), a greater ozone level can then be highly expected.
Fig.1. Tropospheric Ozone and Aerosol Index over Indonesia on July 21, 1997 (from NASA)
Aerosols are concentrations of exceedingly small particles suspended in the atmosphere. Its size ranges from about 0.01 micrometer to 100 micrometers in diameter. The aerosol particles that directly form pollution may be as small as 1 millimeter in size. The particles near Earthâ€™s surface come from both natural and anthropogenic processes. The natural sources include volcanoes emission, the dust from the desert, and the volatile organic compounds (VOCs) created by plants.
Sulfur emissions play an important role in aerosols formation. Other chemicals like ammonia and NOx are also involved in this overall process. Current measurement reveals that the generous fractions of aerosols are a by-product of human activities in the lower atmosphere. The visible smog that comes from the burning of fossil fuels consists of organic and sulfate compound (mainly SO2 and organic gases). The concentration of SO2 in the Northern Hemisphere has increased dramatically in the last hundreds of years. While the amount of SO2 is currently decreasing in the US, it is still rising among the industrialized countries such as India and China. (Cooke et al., 2002)
Fig. 3. Annual average surface temperature variation in response to time-dependent tropospheric ozone change. Results are averages over the five ensemble members for the northern and southern extratropics, the tropics, and the entire globe, all smoothed with a 10-year running mean. Values are given relative to the 1880â€“1890 ensemble mean. (Enhanced EPS)
Fig. 2, Total Sulfur Emissions from 1850~2000 (Enhanced EPS)
3. MODEL DISCRIPTIONS
One of the useful ways to evaluate the impact of troposphere ozone on atmospheric temperature is using the 3D ozone fields simulations. This climate model uses the ozone fields for its radiative calculations.
The modal used in Goddard Institute for Space Studies (GISS) simulations is to percolate ozone and aerosol change for IPCC Fourth Assessment report. The unified tropospheric chemistry-aerosol model within the GISS GCM IIâ€² [Liao et al., 2003, 2004; Liao and Seinfeld, 2005] is used here. This GISS model has been used extensively to investigate the climate response to, solar radiance, and tropospheric ozone and aerosol burdens. A recent temperature dependent simulation was performed with a similar model version using the ocean model of Russell et al. (1995). A collection of five runs from 1880 to 2003 was performed.