The Contribution of Large-scale Atmospheric Patterns to PM10 Pollution: The New Saharan Oscillation Index

Abstract

ABSTRACT PM10, an urban air pollutant that originates from both natural and anthropogenic sources (desert dust and industrial and traffic emissions), reduces visibility and threatens human health, particularly in large cities. Casablanca, which exhibits the highest urbanization rate and population density in Morocco, possesses a concentration of industrial units as well as a large vehicle fleet. Marrakech, another of the most populated cities in the country, has also witnessed an increased rate of motorization during the recent years. The primary objective of this study was to evaluate the relationship between the atmospheric circulation and the PM10 concentrations in Casablanca and Marrakech (based on daily measurements from 2013 to 2016). First, we assessed the correlations between the concentrations and the climate indexes (the North Atlantic Oscillation [NAO] and the Mediterranean Oscillation [MO]). Then, we characterized the contribution of large-scale atmospheric patterns related to extreme PM10 events. Finally, we created the Saharan Oscillation Index (SaOI), a climate index for characterizing the oscillation in the country’s southern desert, between the Saharan depression and the Azores High, and calculated its time series. Our results elucidate the relationship between the MO and the average PM10 concentrations, demonstrating that particulate pollution in the study area is partly induced by a northeasterly to southwesterly continental flow that is triggered by the Saharan trough and influenced by the high-pressure area in the north. The significant statistical correlations, mainly found in winter, confirm the relationships between the Saharan Oscillation Index, the average PM10 concentrations and the MO and NAO indexes—and thus the applicability of the SaOI—during this season.