Beryllium-7 measurements in the Houston and Phoenix urban areas: an estimation of upper atmospheric ozone contributions.

Natural radionuclides have been proposed as a means of assessing the transport of ozone (O3) and aerosols in the troposphere. Beryllium-7 (7Be) is produced in the upper troposphere and lower stratosphere by the interaction of cosmogenic particles with atmospheric nitrogen and oxygen. 7Be has a 53.29-day half-life (478 keV gamma) and is known to attach to fine particles in the atmosphere once it is formed. It has been suggested that O3 from aloft can be transported into rural and urban regions during stratospheric-tropospheric folding events leading to increased background levels of O3 at the surface. 7Be can be used as a tracer of upper atmospheric air parcels and the O3 associated with them. Aerosol samples with a 2.5-microm cutoff were collected during 12-hr cycles (day/night) for a 30-day period at Deer Park, TX, near Houston, in August-September of 2000, and at Waddell, AZ, near Phoenix, in June-July of 2001. A comparison of 7Be levels with 12-hr O3 averages and maxima shows little correlation. Comparison of nighttime and daytime O3 levels indicate that during the day, when mixing is anticipated to be higher, the correlation of 7Be with O3 in Houston is approximately twice that observed at night. This is consistent with mixing and with the anticipated loss of O3 by reaction with nitric oxide (NO) and dry deposition. At best, 30% of the O3 variance can be explained by the correlation with 7Be for Houston, less than that for Phoenix where no significant correlation was seen. This result is consistent with the intercept values obtained for 7Be correlations with either O3 24-hr averages or O3 12-hr maxima and is also in the range of the low O3 levels (25 ppb) observed at Deer Park during a tropical storm event where the O3 is attributable primarily to background air masses. That is, maximum background O3 level contributions from stratospheric sources aloft are estimated to be in the range of 15-30 ppb in the Houston, TX, and Phoenix, AZ, area, and levels above these are because of local tropospheric photochemical production.

Surgical treatment and outcome of patients with giant retinal tears.

OBJECTIVE: To report the management and outcome in retinal detachments associated with giant retinal tears (GRTs). METHODS: Retrospective, case note analysis of patients treated between November 1991 and June 2002 at a tertiary referral hospital. RESULTS: The case notes of 29 patients (24 males, 5 females) with a follow-up ranging from five months to 7 years were reviewed. In all, 25 eyes had retinal detachments with macular involvement and 10 patients had myopia more than 6 D. All patients underwent vitrectomy. A total of 23 patients had heavy liquid and 16 had scleral explants; 28 patients had silicone oil and one had C3F8 tamponade. Intraoperative complications included lens trauma and iatrogenic GRT. Six eyes had recurrent retinal detachment and needed multiple surgical procedures. At the last follow-up, 25 patients had anatomically attached retinas. In all, 18 fellow eyes were treated prophylactically. Three patients had total retinal detachment and marked PVR. The visual acuity improved in 20 eyes. CONCLUSION: GRTs are more common in patients with high myopia. With newer techniques of surgical treatment of GRTs, the anatomical and visual outcomes are more favourable.