Stratospheric ozone isotope fractionations derived from collected samples

Abstract

1] Oxygen isotope ratios in ozone show an unusual enrichment when compared with expected values. New results are reported that have been determined from samples collected in the stratosphere on board balloons. Flights were conducted from three locations, near the equator, at middle latitudes, and in the polar region. To about 27 km the temperature of the atmosphere determines the isotope enrichment of the two heavy isotopes 49O3 and 50O3; above that altitude the enrichments increase more strongly. Highest values measured near the equator are 13% in 50O3 and 10% in 49O3 around 32 km, implying an additional photolysis-induced isotope effect which accounts for 1/4 of the total enrichments measured. Results above Kiruna, Sweden, show a marked increase in heavy ozone from early winter to early summer in agreement with laboratory studies which established the significance of the gas temperature during ozone production. The new data quantitatively establish an additional enrichment in heavy ozone for the upper stratosphere. It is more pronounced near the equator than at middle latitudes and was not detectable in the polar region.