Correlations between extinction parameters for both photometric (blue circles) and non-photometric nights (red points). No strong correlations are seen between pressure, ozone, or telluric H₂O and O₂. The aerosol parameters τ and å are correlated because they represent the same physical component. The distributions of the parameter values (diagonal plots) also are similar on photometric and non-photometric nights. Note that the incidence of aerosol exponents near å ~0 is suppressed on non-photometric nights since the grey extinction term can completely compensate for this case.