A Multi Isotope Approach to Understanding Aerosol Formation, Transformation and Climate: From 3.8 Billion Years Ago to Present. Earth and Mars (Invited Keynote Presentation)

The formation of atmospheric aerosols, their chemical transformation and perturbation on the earth's climate and oxidation state have been recognized for decades. Chemistry on the liquid layer of the aerosols is also an important process but notroioulsy difficult to measure. An array of experimental and theoretical approaches on achieving a maximal understanding of their properties, chemical changes, and interaction with the global and local environment is mandatory, especially to predict future impact and potential consequences of the earths atmosphere-surface environment.

The use of isotope ratios of aerosols have been done for decades and new information gathered, particularly for sulfate. In the case of sulfate, with 4 stable isotopes of sulfur, three isotopes of oxygen, and a naturally produced 35S isotope (87 day half life) an enormous amount of chemical oxidative information is stored, including ozone/oxygen chemistry in the troposphere and stratosphere is available.We have developed all techniques to measure all of these systems on a single sample.The sulfur isotopes yield information on both the source and photochemistry of its precursor sulfur dioxide, especially to the stratosphere, such as El Nino, volcanoes, and massive biomass burning processes. The inclusion of measurements of the 35S radioactivity in SO2 and SO4, a chronometer of the actual gas to particle process is available to determine the actual rate. This is the only clock available to directly measure the nucleation rate of sulfate aerosols, or any aerosol. The half life of 87 days is exactly right to make these measurements and is extremely sensitive.

Using this array of isotope measurements, coupled with basic laboratory measurements of the fundamental physical chemical processes, deeper understanding of a variety of process are studied. This includes long range transport (Asia-California; equator to poles), oxidation/nucleation rates, stratospheric chemical perturbations from volcanoes over the past 400 years,and definition of the interaction of aerosols on the overall oxidation capacity of the Earth. Measurements of samples from the Tibetan plateau have shown how isotopes probe deeper into details of the stratosphere-troposphere exchange processes, and the impact of aerosols on the rate of ice melting in the glaciers supplying 65% of the worlds drinking water. The same measurement in aerosols that later are incorporated into the ice and rock record are stored and offer views into the recent (decadal) and past (3.8 billion year)and provide climate and atmospheric information that could not have been acquired by any other technique.Ice core measurements across the Holocene detail the oxidation state changes through glaciation periods. The impact on climate by volcanoes (such as the year of no summer) have also been detected as well as the details of the chemical perturbation of Pinatubo, El Chichon and Cerro Hudson. Such information are critical in providing the deepest understanding of the Earth's upper atmosphere This presentation will describe the use of the wide isotopic measurements of multi isotopes in determining global atmospheric chemistry, interaction with aerosols, and our development of understanding the perturbation history of the Earth's climate. The understanding of the Earths system is also understood by comparing to the same formation and transformation process in another natural environment, Mars, and its change over the same time scale.