Ozone and NO2 variations measured during the 1 August 2008 solar eclipse above Eureka, Canada with a UV‐visible spectrometer

On 1 August 2008, a solar eclipse of 98% totality passed over the Polar Environment Atmospheric Research Laboratory at Eureka, Canada (80.05°N, 86.42°W), which is run by the Canadian Network for the Detection of Atmospheric Change. During the eclipse, a zenith‐sky UV‐visible spectrometer measured slant column densities (SCDs) and vertical column densities (VCDs) of ozone up to 82% occultation and NO2 up to 96% occultation, beyond which low light intensities and changes in the solar spectrum due to limb darkening compromised data quality. Ozone VCDs during the eclipse remained within natural variability, and this study is inconclusive regarding ozone oscillations due to limited temporal resolution and measurement errors toward eclipse maximum. Measured NO2 SCDs increased and decreased symmetrically around the eclipse maximum. NO2 SCDs were also calculated using a photochemical box model and a one‐dimensional radiative transfer model. The modeled ratio of eclipse day SCDs to the previous day's SCDs was compared to the measurements. They agreed within error bars leading up to maximum occultation, but the model ratio was systematically larger than the measured ratio for the second half of the eclipse, perhaps due to changing cloud conditions throughout the eclipse. The measured NO2 SCD ratio of 1.84−0.43+0.12 at 96% totality is larger than observed in past studies and agrees with modeled ratio of 1.91. Therefore our current understanding of stratospheric photochemistry is sufficient to predict the evolution of NOx chemistry through a solar eclipse.