Characterization of water-soluble inorganic ions and carbonaceous aerosols in the urban atmosphere in Amman, Jordan

Abstract

The urban particulate matter (PM) carbonaceous and water-soluble ions were investigated in Amman, Jordan during May 2018–March 2019. The PM_2.5 total carbon (TC) annual mean was 7.6 ± 3.6 μg/m³ (organic carbon (OC) 5.9 ± 2.8 μg/m³ and elemental carbon (EC) 1.7 ± 1.1 μg/m³), which was about 16.3% of the PM_2.5. The PM₁₀ TC annual mean was 8.4 ± 3.9 μg/m³ (OC 6.5 ± 3.1 μg/m³ and elemental carbon (EC) 1.9 ± 1.1 μg/m³), about 13.3% of the PM₁₀. The PM_2.5 total water-soluble ions annual mean was 7.9 ± 1.9 μg/m³ (about 16.9%), and that of the PM₁₀ was 10.1 ± 2.8 μg/m³ (about 16.0%). The minor ions (F⁻, NO₂⁻, Br⁻, and PO₄³⁻) constituted less than 1% in the PM fractions. The significant fraction was for SO₄²⁻ (PM_2.5 4.7 ± 1.6 μg/m³ (10.0%) and PM₁₀ 5.3 ± 1.9 μg/m³ (8.3%)). The NH₄⁺ had higher amounts of PM_2.5 (1.3 ± 0.6 μg/m3; 2.7%) than that PM₁₀ (0.9 ± 0.4 μg/m³; 1.4%). During sand and dust storm (SDS) events, TC, Cl⁻, and NO₃⁻ were doubled in PM, SO₄²⁻ did not increase significantly, and NH₄⁺ slightly decreased. Regression analysis revealed: (1) carbonaceous aerosols come equally from primary and secondary sources, (2) about 50% of the OC came from non-combustion sources, (3) traffic emissions dominate the PM, (4) agricultural sources have a negligible effect, (5) SO₄²⁻ is completely neutralized by NH₄⁺ in the PM_2.5 but there could be additional reactions involved in the PM₁₀, and (6) (NH₄)₂SO₄, was the major species formed by SO₄²⁻and NH₄⁺ instead of NH₄HSO₄. It is recommended to perform long-term sampling and chemical speciation for the urban atmosphere in Jordan.