A decade of satellite observations reveal significant increase in atmospheric formaldehyde from shipping in Indian Ocean

Abstract

Atmospheric formaldehyde (HCHO) is a potential pollutant and very harmful to public health at higher doses. There are different sources for HCHO in the atmosphere, in which fuel combustion and biomass burning are predominant. The oxidation of hydroxyl radicals (OH) and methane are the chemical production pathways of HCHO in the troposphere. Here, we show a different source of HCHO emission to the atmosphere; the maritime shipping. The analyses using satellite measurements for the period 2005–2014 reveal large amounts of HCHO release along the ship routes in Indian Ocean, about 7–8 x1015 molec./cm2. This is nearly twice (150–200%) the ambient or background HCHO levels (about 4 × 1015 molec./cm2), when there is no ship emissions in the north Indian Ocean. The trend in HCHO concentrations over the Indian Ocean sea routes is about 0.008 × 1015 molec./cm2/year. The amount and the increasing trends of HCHO over the maritime routes in the north Indian Ocean are also comparable to those of the busiest sea-lanes in the world Oceans, such as the Panama Canal, Mediterranean Sea and Strait of Malacca. Our analyses, henceforth, suggest use of a better fuel for shipping to reduce the maritime pollution, as the polluted air can often be transported to the coastal regions and islands, which is a concern for public health in those regions.