Modelling the spatial patterns and recent trends of multiple air pollutants in Romania based on long-term gridded...

While air pollution is a major global environmental challenge, its current status and recent changes remain insufficiently explored in many countries worldwide, including Romania. This study provides the first comprehensive and nationwide assessment of the current patterns and recent spatio-temporal trends (1990-2022) for nine major air pollutants (NO_x, SO_x, CO, NMVOC, NH₃, BC, PM₂.₅, PMc, and PM₁₀) in Romania. In this context, we performed a Geographic Information Systems (GIS)-based spatial analysis integrated with robust statistical methods to evaluate the current spatial distribution and total amounts of air pollutants, as well as to detect their long-term spatio-temporal trends at the pixel level. More precisely, the multifaceted atmospheric pollution was examined based on its current spatial patterns (derived from mean multiannual values and other metrics) and total emission amounts (expressed in Mg or metric tons), while the spatio-temporal trends of air pollutants were investigated using Sen's slope estimator and the Mann-Kendall test, to detect their magnitude and statistical significance from national to regional (territorial) scales. Our geospatial findings highlight complex geographic patterns of air pollution in terms of mean spatial distribution, dominated by urban pollution hotspots, in contrast to the mountain (Carpathian) areas hosting the lowest national pollution levels. Quantitatively, the results reveal that Romania released over 83 million Mg of air pollutants since 1990, of which most emissions were represented by CO (nearly 40% of the total), followed by SO_x (17%), NMVOC (12%) and NO_x (12%). Dynamically, however, our findings revealed widespread (generally >50% of Romania's area) statistically significant negative trends for SO_x, NO_x, CO, NMVOC, and NH₃, alongside large-scale (>60-70%) positive trends for BC and particulate matter. The results provide a robust, inventory-based foundation for assessing air pollution in Romania, serving as a strategic framework for optimizing future air quality policies and national pollution control measures.