Carbon Dioxide and Oxygen Isotope Anomalies in the Mesosphere and Stratosphere

Abstract

provide a conclusive demonstration of the principle of the enhancement of nonlinear optical response through the supramolecular engineering of polymers. It is expected that considerably larger enhancement can be observed in structures with better alignment of chromophores, such as certain biopolymers and derivatives of helical poly(tripheny1methylmethacrylate)~ (1 6).

Oxygen isotopic composition of carbon dioxide in the middle atmosphere

“…The disagreement of the 1D model vertical profiles shown in Fig. 4 with the measurements of Thiemens et al (10) is due to circulation cells between the tropics and Ϸ30°N, where the air is significantly younger than that at higher latitudes with similar altitudes (refs. 13 and 21 and M.-C.L., G.A.B., and Y.L.Y., unpublished data).…”

“…These cross-sections, together with the solar spectrum, yield enormous fractionation factors and calculated values of ␦ 17 O( 1 D) and ␦ 18 O( 1 D) resulting from O 2 photolysis that peak at Ϸ80 km with sizes of 3137.1 and 10578.6 per mil, respectively. The resulting m Ϸ 0.3 means that even small amounts of mixing of mesospheric air with the m ϭ 1.6 gas that characterizes the stratosphere can provide an explanation for the m Յ 1.2 fractionation observed in CO 2 by Thiemens et al (10). We stress that Lyman-␣ photolysis of O 2 as a source of heavy O( 1 D) has not been considered in previous models.…”

“…Here we present such an analysis along with a simple 1D diffusive transport simulation to assess the relative importance of stratospheric and mesospheric sources of O( 1 D) to the isotopic composition of CO 2 in the middle atmosphere. To avoid uncertainties due to stratosphere-troposphere exchange processes, possible contamination from tropospheric water, and seasonal and latitudinal variations of tropospheric CO 2 isotopologues, we place our focus here only on the data that have been taken well above the tropopause (8,10).…”

“…Despite the large uncertainties in m, induced by the challenges associated with the sample collection and mass spectrometry of middle atmospheric O 3 (2,5) and CO 2 (8,10,11), it is worth examining the potential sources of variation in the isotopic composition of carbon dioxide, both to better understand the atmosphere and as a guide for future observations. Yung et al (13), for example, have suggested that the upwelling of tropospheric air from the tropics along with downwelling near 30°N could dilute the magnitude of the fractionation induced by photochemistry.…”

“…Higher in the mesosphere, we discover that the photolysis of 16 biogeochemical cycles ͉ CO2 ͉ mesosphere ͉ stratosphere O f the many trace molecules that can be used to examine atmospheric transport processes and chemistry [e.g., CH 4 , N 2 O, SF 6 , and the chlorofluorocarbons (CFCs)], carbon dioxide is unique in the middle atmosphere, because of its high abundance [Ϸ370 parts per million by volume (ppmv) in the stratosphere, dropping to Ϸ100 ppmv at the homopause]. The massindependent isotopic fractionation of oxygen first discovered in ozone (1)(2)(3)(4)(5)) is thought to be partially transferred to carbon dioxide (3,(6)(7)(8)(9)(10)(11) via the reaction O( 1 D) ϩ CO 2 in the middle atmosphere (12,13). Indeed, whereas the reactions of trace molecules with O( 1 D) usually lead to their destruction (14), the O( 1 D) ϩ CO 2 reaction regenerates carbon dioxide.…”