Seasonal Variations and Composition of Soluble Ions in PM_2.5 at an Urban Location in Kenitra, Morocco

Abstract

A comprehensive study was executed within the urban vicinity of Kenitra city, covering the period from 2020 to 2021. During this study, 60 effective PM2.5 samples were collected in a period of 24 h using a dichotomous sampler and Nuclepore track-etched polycarbonate filters with a diameter of 37 mm. Ion chromatography was employed to identify the composition of our samples, including Cl−, SO42−, F−, NO3−, NH4+, Na+, Ca2+, and K+. The results showed that the average mass concentration (± standard deviation) of the seven ions in PM2.5 was 3.2 ± 1.3 µg/m3, constituting approximately 18% of the total mass concentration. Among the ions, the concentrations followed the order of Na+ > SO42−> Cl− > NO3−> K+ > NH4+ > F−. The predominant constituents of water-soluble ions in PM2.5 were detected to be secondary inorganic species (NH4+, SO42−, and NO3−), contributing an average of 44% to the total PM2.5 ions. Throughout the four seasons, the concentrations of these three ions exhibited variability, with the greatest levels observed in spring, followed by summer, fall, and winter. The ratio of [NO3−]/[SO42−] was found to be almost equal to unity, indicating that the primary sources of nitrogen and sulfur in the Kenitra atmosphere were prioritized from stationary sources (typically associated with power plants, industrial and commercial activities, and other large-scale facilities).

Keywords

• PM_2.5
• water-soluble ions
• seasonal variations
• urban aerosols
• ion chromatography