An investigation into NO2 column concentrations in the Sahara Desert region: relationships with other pollutants

Abstract

The investigation of atmospheric complex pollutant relationships in the Sahara Desert, the largest desert located in northern Africa, constitutes a critical component of global environmental research. This study analyzed the intricate interactions among NO₂, HCHO, and O₃ in the Sahara Desert region (encompassing Algeria, Libya, and Egypt) using temporal and spatial distributions derived from OMI sensor data, the HYSPLIT model, and ozone-sensitive control areas. The analysis revealed their spatial and temporal distributions, trans-regional transport pathways, and the dominance of ozone as a pollutant. Results indicated that the annual changes in the spatial distribution of NO₂, HCHO, and O₃ exhibited an increasing trend from south to north. Temporally, NO₂ showed a wavy pattern with a peak in 2017, HCHO displayed an inverted V pattern peaking in 2018, and O₃ followed a Z pattern with a peak in 2017. Monthly variations showed that both NO₂ and O₃ were highest in summer, followed by spring, autumn, and winter, while HCHO peaked in winter, followed by autumn, summer, and spring. Exogenous atmospheric transport significantly influences NO₂ pollution in the Sahara Desert, as demonstrated by the HYSPLIT model’s analysis of backward trajectories and potential source areas over a decade of rainy and dry seasons. High-pollution areas are primarily affected by the southeastern Mediterranean monsoon and the southeastern Algiers winds. Annual spatial variations within ozone-sensitive control areas indicate that ozone is predominantly influenced by VOCs and NOx synergistic control. Monthly spatial variations show that NOx control dominates in autumn and winter, while VOCs control prevails in summer and fall.