Quantification of ozone reductions within the Saharan air layer through a 13-year climatologic analysis of ozone profiles

Abstract

Ozone (O3) reduction caused by dust particles is a challenging topic that has not been sufficiently investigated. Previous studies have provided limited quantification of O3, mainly based on case studies or short-term campaigns. In this paper, 157 O3 vertical profiles from ozone soundings launched from the Canary Islands over 13 summers are analyzed. Using aerosol optical depth as a discrimination tool, the data are classified into two groups: clean atmospheric conditions and dusty conditions under the presence of the Saharan Air Layer (SAL). The results show that ozone mixing ratios on SAL days are systematically lower than those during clean conditions, with a difference of as much as 35%. An analysis of independent total ozone columns from ground-based and satellite spectrometers confirm the observed O3 reductions. In addition, a vertical redistribution of the total water content takes place during these events. A comparison of the vertical shape of the O3 reductions with the vertical distribution of dust loading and precipitable water vapor shows that although O3 reductions occur in parts of the layer where the dust is present, a better correlation is found with the total amount of water present in the air. This finding suggests that the latter component plays a role in the observed O3 reduction within the SAL.