Synergistic effect of the occurrence of African dust outbreaks on atmospheric pollutant levels in the Madrid metropolitan area

Abstract

The occurrence of African dust outbreaks over specific areas of the Mediterranean basin has been associated with increases in the PM 10 concentration levels and also in the mortality rates. Different hypothesis have been proposed in the last years to explain the processes by which African dust storms generates negative health effect over urban areas in southern Europe but are still not clear. Some authors have suggested the existence of an interaction between air pollutants from local sources and the occurrence of African dust outbreaks, with a consequent increase in the risk of mortality due to exposure to these anthropogenic emissions. This study sought to identify such a synergistic effect in the Madrid metropolitan area. To this end, an assessment of the influence of African dust on air quality levels, the vertical structure of the atmosphere over Madrid and daily mortality was carried out. Our results indicated that African dust caused a reduction of the mixing layer height and the surface wind speed, by reducing the amount of solar radiation reaching the ground. These facts favored the accumulation of air pollutants emissions from local anthropogenic sources. Moreover, when the dust contribution to PM 10 levels exceeded a threshold value (8 μg/m 3), particulate matter mass (PM 10 , PM 2.5) and number (ultra-fine particles) concentration as well as levels of gaseous air pollutants (CO, NO and NO 2) registered at urban-background and urban-traffic monitoring sites, increased with statistical significance. In these conditions, it was found a statistically significant increase in risk of daily mortality in the PM 10 exposure. Hence, ambient air in Madrid was more toxic during African dust events of increasing intensity due to this synergistic effect. Because it can be envisaged that the frequency, duration and intensity of dust storms will increase in the north of Africa due to climate change, it will be a priority to put forward and assess proposals to mitigate the adverse effects on health, focused on the reduction of air pollutant emissions from local sources, as well as proposals regarding the adaptation of the population in urban areas across the Mediterranean basin.

Do Saharan Dust Intrusions Affect the Incidence and Severity of COVID-19 in Spain?

“…Days with Saharan dust intrusion not only produce increases in concentrations of PM 10, they also result in increases in the concentrations of other pollutants such as NO 2 , although in our analysis, there were only statistically signi cant increases in Gran Canaria and Madrid. These results coincide with what has been found in other studies that analyze the evolution of primary pollutants on days with and without Saharan dust intrusion in the cities of Barcelona (Pandol et al, 2014) and Madrid (Salvador et al, 2019) and in other Spanish cities (Moreira et al, 2020). According to these studies, the reason for this increase is the existence of particulate material on days with Saharan dust intrusion, which produces a decrease in solar radiation and a consequent decrease in the convective turbulence processes that cause a vertical development of the mixing cap during the day.…”

“…Another possible hypothesis could be related to the fact that a decrease in the mixing cap is produced when there is a Saharan dust intrusion (Pandol et al, 2017;Salvador et al, 2019). A decrease in the mixing cap not only affects the increase in primary pollutants, including those we have included in this study, PM 10 and NO 2 , but it also makes the dispersion of other pollutants and increase in aerosols more di cult (Li et al, 2017).…”

Impact of environmental factors and Sahara dust intrusions on incidence and severity of COVID-19 disease in Spain. Effect in the first and second pandemic waves

“…Days with Saharan dust intrusion not only produce increases in concentrations of PM 10 , they also result in increases in the concentrations of other pollutants such as O 3 . These results coincide with what has been found in other studies that analyze the evolution of pollutants on days with and without Saharan dust intrusion in the cities of Barcelona (Pandolfi et al 2014 ) and Madrid (Salvador et al 2019 ) and in other Spanish cities (Moreira et al 2020 ). According to these studies, the reason for this increase is the existence of particulate matter on days with Saharan dust intrusion, which produces a decrease in the convective turbulence processes that cause a vertical development of the mixing layer during the day.…”

Impacts of Desert Dust Outbreaks on Air Quality in Urban Areas

“…For example, the adverse health effects or toxicity of the locally produced particulate matter was also found to increase during dust outbreaks [21]. Studies in southern Europe (Barcelona and Madrid, Spain) have found that the mixing layer height significantly decreased with increasing intensity of Saharan dust events [22,23] and that an increased risk of mortality was observed with the reduction in mixing layer height [22]. This thinning of the mixing layer leads to an accumulation of local anthropogenic pollutants and may favour new particle formation or new species formed from condensation of gaseous precursors on the surface of dust particles [22,24].…”