Influence of the ozone profile above Madrid (Spain) on Brewer estimation of ozone air mass factor

摘要

The methodology used by Brewer spectroradiometers to estimate the ozonecolumn is based on differential absorption spectroscopy. This methodologyemploys the ozone air mass factor (AMF) to derive the total ozone columnfrom the slant path ozone amount. For the calculating the ozone AMF, theBrewer algorithm assumes that the ozone layer is located at a fixed heightof 22 km. However, for a real specific site the ozone presents a certainprofile, which varies spatially and temporally depending on the latitude,altitude and dynamical conditions of the atmosphere above the site ofmeasurements. In this sense, this work address the reliability of thementioned assumption and analyses the influence of the ozone profilesmeasured above Madrid (Spain) in the ozone AMF calculations. Theapproximated ozone AMF used by the Brewer algorithm is compared withsimulations obtained using the libRadtran radiative transfer model code. Theresults show an excellent agreement between the simulated and theapproximated AMF values for solar zenith angle lower than 75°. Inaddition, the relative differences remain lower than 2% at 85°.These good results are mainly due to the fact that the altitude of the ozonelayer assumed constant by the Brewer algorithm for all latitudes notably canbe considered representative of the real profile of ozone above Madrid(average value of 21.7±1.8 km). The operational ozone AMF calculationsfor Brewer instruments are limited, in general, to SZA below 80°.Extending the usable SZA range is especially relevant for Brewer instrumentslocated at high mid-latitudes.