METO 637 Lesson 9

Man’s impact on the Stratosphere The concern over a loss of stratospheric ozone is that this will lead to an increase in ultraviolet radiation at the ground, especially those wavelengths near 300 nm. The next figure shows the so-called action spectra for biological response. The action spectra also follows closely the absorption spectra for DNA, which leads to the dissociation of the DNA molecule. This could lead to cell mutations – skin cancer. We identify a spectral intervals of interest, UV-B from 280 to 315 nm. Although skin cancer gets most of the publicity, it also impacts the biota.

DNA absorption and the solar flux at the surface

Human death due to skin melanoma

Supersonic Aircraft First real concern was the role of supersonic transport (SST) which were to fly in the stratosphere. These aircraft emit water vapor, CO, and NO X directly into the stratosphere, where they could accumulate over two years. The NO comes from heating the air at high temperatures: N 2 + energy → N + N N + O 2 → NO + O O + N 2 → NO + N The reaction rates can become large at high temperaures, e.g. in the cylinders of automobiles. This cycle is known as the Zeldovich mechanism. The water vapor and CO come from the oxidation of the aviation fuel. Initially a projected fleet of 500 aircraft emitting 1.2E+9 kg of NO per year was assumed.

Supersonic Aircraft Initially it was thought that the injected water vapor was the major problem, after the work of Bates and Nicolet. These reactions are OH + O 3 → HO 2 + O 2 HO 2 + O → OH + O 2 net reaction O + O 3 → O 2 + O 2 And OH + O 3 → HO 2 + O 2 HO 2 + O 3 → OH + O 2 Net O 3 + O 3 → 3O 2 In the US this concern led to the formation of the CIAP program (Climatic Impact Assessment Program).

Supersonic Aircraft Then Paul Crutzen (theorist) put forward the NO X catalytic cycle and Harold Johnson (laboratory chemist) showed that the reaction rates would make the catalytic cycle significant. These reactions are: NO + O 3 → NO 2 + O 2 NO 2 + O → NO + O 2 net reaction O + O 3 → O 2 + O 2 The fleet of 500 SST’s would have led to a reduction in the global ozone column of about 12%.

Potential atmospheric impacts of aircraft emissions

Measured and calculated NOx` emission indices from aircraft

Typical fuel consumption in Kg

History of calculations of ozone loss from SST’s

Rockets and the Space Shuttle Solid fuel rockets are used as launch vehicles, and to boost the Space Shuttle in its early stages of flight. The oxidizer used in these rockets is ammonium perchlorate. HCl is released into the stratosphere, which can begin the chlorine catalytic cycle. Aluminum is added to the rocket fuel to boost thrust, and the rocket exhaust also contains aluminum oxide particles, which could contribute to heterogeneous chemistry. The following reaction is known to occur on aluminum particles ClONO 2 + HCL → Cl 2 + HNO 3 In general the amount of HCl released is small compared to natural sources of chlorine.