Depletion of tropospheric ozone associated with mineral dust outbreaks

Abstract

From May to September 2012, ozone reductions associated with 15 Saharan dust outbreaks which occurred between May to September 2012 have been evaluated. The campaign was performed at a mountain station located near the eastern coast of the Iberian Peninsula. The study has two main goals: firstly, to analyze the decreasing gradient of ozone concentration during the course of the Saharan episodes. These gradients vary from 0.2 to 0.6 ppb h(-1) with an average value of 0.39 ppb h(-1). The negative correlation between ozone and coarse particles occurs almost simultaneously. Moreover, although the concentration of coarse particles remained high throughout the episode, the time series shows the saturation of the ozone loss. The highest ozone depletion has been obtained during the last hours of the day, from 18:00 to 23:00 UTC. Outbreaks registered during this campaign have been more intense in this time slot. The second objective is to establish from which coarse particle concentration a significant ozone depletion can be observed and to quantify this reduction. In this regard, it has been confirmed that when the hourly particle concentration recorded during the Saharan dust outbreaks is above the hourly particle median values (N > N-median), the ozone concentration reduction obtained is statistically significant. An average ozone reduction of 5.5 % during Saharan events has been recorded. In certain cases, this percentage can reach values of higher than 15 %.

First X-ray Spectroscopic Observations of Atmospheric Titanium Species: Size Dependence and the Emission Source

“…Titanium dioxide (TiO 2 ) has three stable polymorphs including rutile, anatase, and brookite and is employed as a product enhancer, such as TiO 2 -coated building exteriors, pigments, and road pavements, due to its high photocatalytic activity, reasonable costs, and less toxicity. − Photocatalytic reactions of TiO 2 in aerosol particles are one of the drivers of the tropospheric chemistry of inorganic gases (O 3 , NO x , SO x , and HO x ) and volatile organic compounds. − Field-based observations in the actual environment revealed the occurrence of tropospheric O 3 depletion during large mineral dust event. − However, the net effect of the photocatalytic reaction of TiO 2 is still unclear because of the limited number of Ti speciation studies in aerosol samples based on field observations.…”

Ozone Uptake by Clay Dusts under Environmental Conditions

“…Although reactions between gas-phase molecules generally dominate atmospheric chemistry, heterogeneous reactions of gas molecules on surfaces have gained interest in the past decades and have been shown to be of major importance for crucial processes, such as the destruction of the stratospheric ozone layer. − Regarding dust surfaces, a correlation between high dust particle contents and a drop in O 3 concentration in the troposphere has been highlighted. − This drop can be due to either direct or indirect effects; the latter seem to prevail, as exemplified by Bauer et al who showed that removal of HNO 3 by dust from the atmosphere largely lowers the budget of this O 3 precursor. Overall, it suggests that the tropospheric ozone budget is linked with the presence of dust, i.e., of a solid surface available for heterogeneous reactions to take place.…”

Ozone depletion due to dust release of iodine in the free troposphere

“…In our simulations, the iodine source from the Sahara is actively controlled and conservatively estimated by modulating the efficiency of iodine release zonally not to exceed the observed levels of IO radicals in the SAAD domain. Consistent with the SAAD dust, Saharan dust has also been observed to affect O 3 in the free troposphere at the Monte Cimone Climate observatory, with implications for surface air quality in cities of northern Italy [Po Valley; ( 28 )] and southern Spain ( 62 ). This pattern of dust transport is captured by CAM-chem; however, the magnitude of episodic impacts on O 3 of >40% attributed to Saharan dust at Monte Cimone is underestimated in the model, reflecting the conservative implementation of iodine chemistry from Saharan dust (fig.…”