Measurements Addressing Quantitative Ozone Loss, Polar Stratospheric Cloud Nucleation, and Large Polar Stratospheric Particles during Austral Winter and Spring

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The proposal seeks the continuation of in situ balloon-borne ozone observations over Antarctica through 2005. Ozone in the Antarctic stratosphere suffers a much different seasonal cycle today than it has in the past due to the introduction of significant amounts of chlorofluorocarbons into the atmosphere. In the past Antarctic ozone amounts were controlled primarily by global circulation processes leading to wintertime build up of ozone. Today the presence of chlorine coupled with cold temperatures, which create stratospheric clouds, leads to a springtime minimum in ozone due to a catalytic reaction between ozone and chlorine that has been activated on surfaces of the cloud particles. The mechanisms leading to this ozone loss has been the subject of much scientific activity and significant progress has been made; however, open questions remain which require additional ozone and stratospheric particle profile measurements from McMurdo Station. The ozone profile measurements, to be completed about every 3 days during austral spring, will contribute to the observational base for the period of maximum chlorine loading in the stratosphere. This will contribute to the measurement base required to observe the first signs of ozone recovery as stratospheric chlorine declines within the next decade. Measurements of vertical ozone profiles will be one of the important tools used to observe the first signs of the altitude dependent recovery following the decline in stratospheric chlorine. In 2003, it is proposed to collaborate with several European colleagues in an international Antarctic Match campaign to obtain detailed, altitude dependent, ozone loss rate measurements for comparisons with chemical transport models and photochemical box models. In addition, the polar stratospheric cloud (PSC) observations will be continued to address questions related to the nucleation of nitric acid hydrates, the existence of large particles within Antarctic PSCs and their role in denitrification, and the index of refraction of PSC particles. The instruments on the balloons will provide high-resolution trajectory measurements, which can be used to assess the accuracy of air parcel temperature histories. This information, coupled with in situ aerosol profile measurements and a microphysical model, will be used to test various PSC nucleation hypotheses, which have direct implications for chlorine activation and denitrification. The instrument will be developed with support from a Major Research Infrastructure instrument development award from NSF.