Removal of Stratospheric O$_3$ by Radicals: In Situ Measurements of OH, HO$_2$, NO, NO$_2$, ClO, and BrO

• Published in: Science (American Association for the Advancement of Science) Vol. 266; no. 5184; pp. 398 - 404
• Main Authors: Wennberg, P. O., Cohen, R. C., Stimpfle, R. M., Koplow, J. P., Anderson, J. G., Salawitch, R. J., Fahey, D. W., Woodbridge, E. L., Keim, E. R., Gao, R. S., Webster, C. R., May, R. D., Toohey, D. W., Avallone, L. M., Proffitt, M. H., Loewenstein, M., Podolske, J. R., Chan, K. R., Wofsy, S. C.
• Format: Journal Article
• Language: English
• Published: American Society for the Advancement of Science 21-10-1994
• Subjects: Aerosols; Air masses; Altitude; Chlorine; Free radicals; Halogens; Mixing ratios; Ozone; Photolysis; Stratosphere
• ISSN: 0036-8075; 1095-9203
• DOI: 10.1126/science.266.5184.398

Simultaneous in situ measurements of the concentrations of OH, HO$_2$, ClO, BrO, NO, and NO$_2$ demonstrate the predominance of odd-hydrogen and halogen free-radical catalysis in determining the rate of removal of ozone in the lower stratosphere during May 1993. A single catalytic cycle, in which the rate-limiting step is the reaction of HO$_2$ with ozone, accounted for nearly one-half of the total O$_3$ removal in this region of the atmosphere. Halogen-radical chemistry was responsible for approximately one-third of the photochemical removal of O$_3$; reactions involving BrO account for one-half of this loss. Catalytic destruction by NO$_2$, which for two decades was considered to be the predominant loss process, accounted for less than 20 percent of the O$_3$ removal. The measurements demonstrate quantitatively the coupling that exists between the radical families. The concentrations of HO$_2$ and ClO are inversely correlated with those of NO and NO$_2$. The direct determination of the relative importance of the catalytic loss processes, combined with a demonstration of the reactions linking the hydrogen, halogen, and nitrogen radical concentrations, shows that in the air sampled the rate of O$_3$ removal was inversely correlated with total NO$_x$ loading.