Charles Thomas McElroy

Retrieval of stratospheric NO2 vertical profiles from ground- based zenith-sky DOAS measurements : Results for the MANTRA 1998 field campaign

Abstract The importance of measurements of the vertical distribution of odd nitrogen in studies of ozone chemistry and climate change has long being recognized. In this paper, we use the optimal estimation method developed by Rodgers (1976, 1990) to retrieve NO2 vertical profiles from slant column observations made with a portable ultraviolet (UV)‐visible zenith‐sky spectrometer operated on the ground during the Middle Atmosphere Nitrogen TRend Assessment (MANTRA) balloon campaign carried out at Vanscoy, Saskatchewan, Canada (52°N, 107°W), from 18 to 25 August 1998. Late summer was chosen for the campaign because the stratospheric zonal wind velocity changes sign at that time. Under such conditions the stratospheric winds are at a minimum, leaving the stratosphere in a dynamically quiescent state and closer to photochemical control (Fahey et al., 2001; Fioletov and Shepherd, 2003). The NO2 profile retrieved from the ground‐based observations is compared with the co‐located and simultaneous NO2 profile measured by a balloon‐borne UV‐visible spectrometer during sunrise on 24 August. Good agreement is observed, giving us confidence in the retrieval technique adopted. The retrieved NO2 profiles are also compared with the output of the Model for Evaluating oZONe trends (MEZON) 3D stratospheric chemical transport model. It is observed that, for altitudes below the peak concentration, the model underestimates the NO2 amount, and at the altitude of peak concentration, the model values lie between the values measured from the balloon and those retrieved from the ground‐based measurements. Nevertheless, the model reproduces the general shape of the retrieved profiles, including the altitude of the NO2 maximum, for both sunrise and sunset conditions.

Measurements of arctic total ozone during the polar winter

Abstract Ground‐based measurements of total ozone were made during the polar night from Arctic stations in the winters of 1987–88 and 1988–89. The measurements were made with automated Brewer ozone spectrophotometers using the moon as a light source. Data were obtained from Alert and Resolute in Canada for both winters and from Heiss Island, USSR, for the second winter. The method of measurement is briefly reviewed and data from the three stations are presented. The ground‐based total ozone measurements are compared with the integrated values derived from ozonesonde profiles.

Retrieval of stratospheric NO/sub 2/ vertical profiles from ground-based measurements at Vanscoy, Saskatchewan

One of the active trace gases that influences the ozone distribution is nitrogen dioxide (NO/sub 2/). Since the role of NO/sub 2/ in the photochemistry of ozone is strongly dependent on altitude, it is important to know not only the NO/sub 2/ total amount, but also its vertical distribution. In this paper, we use the approach proposed by K. E. Preston et al. (1997) to retrieve NO/sub 2/ altitude profiles from slant column measurements. The observations were made with a portable UV-visible spectrometer operated on the ground during the Middle Atmospheric Nitrogen TRend Assessment (MANTRA) balloon campaign carried out at Vanscoy, Saskatchewan, Canada (52/spl deg/ N, 107/spl deg/ W), from 18 to 25 August 1998. The NO/sub 2/ profile retrieved from the ground-based observations is compared with the co-located and simultaneous NO/sub 2/ profile measured by a balloon-borne UV-visible spectrometer during sunrise on August 24. Finally, the retrieved profiles are compared with the output of the MEZON 3D stratospheric chemical transport model and the results are discussed.

Temperature and pressure retrievals from the MAESTRO space instrument

MAESTRO (Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) is a photodiode array spectrometer that will make solar occultation measurements from the SCISAT-1 satellite. The instrument will produce vertical profiles of various constituents with the intent of increasing the understanding of the processes affecting the distribution of ozone in the middle atmosphere. Atmospheric temperature and pressure profiles are necessary for accurate retrievals of aerosols and molecular species. The absorption of solar radiation in the A and B bands of molecular oxygen will be used for retrievals of temperature and pressure on orbit. In support of this goal, the precursor instrument to MAESTRO was flown on August 29, 2000 as part of the main high-altitude balloon payload of the second MANTRA (Middle Atmosphere Nitrogen TRend Assessment) field campaign. Solar occultation measurements made during the balloon flight are being used to test retrieval algorithms for the MAESTRO instrument.