Spatial variation in the association between NO₂ concentrations and shipping emissions in the Red Sea

Air pollution from shipping emissions poses significant health and environmental risks, particularly in the coastal regions. For the first time, this region as one of the busiest seas and most important international shipping lane in the world with significant nitrogen dioxide (NO₂) emissions has been analyzed comprehensively. This paper aims to characterize and quantify the contribution of maritime transport sector emissions to NO₂ concentrations in the Red Sea using local Geographically Weighted Regression (GWR) model in a geographic information system (GIS) environment. Maritime traffic volume was estimated using SaudiSat satellite-based Automatic Identification System (S-AIS) data, and the remotely measured tropospheric NO₂ concentrations data was acquired from the ozone monitoring instrument (OMI) satellite. A significant spatial variation in the NO₂ values was detected across the Red Sea, with values ranging from 4.03 × 10¹⁴ to 41.39 × 10¹⁴ molecules/cm². Most notably, the NO₂ concentrations in international waters were more than double those in the western coastal regions, whereas the concentrations close to seaports were 100% higher than those over international waters. The results indicated that the local GWR model performed significantly better than the global ordinary least squares (OLS) regression model. The GWR model had a strong and significant overall coefficient of determination with an r² of 0.94 (p < 0.005) in comparison to the OLS model with an r² of 0.45 (p < 0.005). Maritime traffic volume and proximity to seaports weighted by shipping activities explained about 94% of the variations of NO₂ concentrations in the Red Sea. The results of this study suggest that the S-AIS data and environmental satellite measurements can be used to assess the impacts of NO₂ concentrations from shipping emissions. These findings should stimulate further research into using additional covariates to explain the NO₂ concentrations in areas near seaports where the standardized residuals are high.