Spatiotemporal variations in aerosol characteristics along the route of the Indian-Atlantic expedition onboard the research vessel Akademik Nikolaj Strakhov

Abstract

We discuss the results of studying the physical-chemical composition of the atmospheric aerosol during expedition onboard the RV Akademik Nikolaj Strakhov carried out during winter of 2015–2016 on the route from Colombo to Kaliningrad (via Suez Canal). As compared to the Mediterranean Sea and Atlantic (near Europe), the atmosphere of the Arabian and Red Seas was characterized by higher values of most aerosol characteristics: 3–5 times larger aerosol optical depth (AOD), 4 times larger aerosol number concentration, 1.5 times larger concentrations of continent- and sea-derived ions, as well as more abundant gas admixtures (SO₂, HCl, HNO₃, NH₃). At the same time, two seas of the Indian basin substantially differ in aerosol composition, primarily due to outflows of aerosols of different types from the continents. The largest concentrations of black carbon (2.14 μg m^–3, on average), sea-derived ions (Na⁺, Cl^–, Mg²⁺), and NH₃ are observed over the Arabian Sea; larger values of the fine component of the AOD and concentrations of “continental” ions (SO₄^2-, Ca²⁺, NO₃^-, NH₄⁺) and gas admixtures SO₂, HCl, HNO₃ are found over the Red Sea. With respect to ion composition of aerosol, most stable concentrations are noted for Ca²⁺ ions (less than 15% difference among the seas), and maximal spatial variations are found for NH₄⁺ ions (the difference of up to a factor of 40).