There is a gradual increase in the concentration of greenhouse gases (GHGs)like CH4 and N2O in ambient air due to intensive agriculture, rapid industrialization and the expanding transport sector. About 80% of N2O is produced biologically and the major sources are agricultural fields, wetlands, sediments, animal
wastes and landfills. Emission of N2O from the soil is due to nitrification and e-nitrification processes.

Molecular chlorine (Cl2) is an important yet poorly understood trace constituent of the lower atmosphere. Although a number of mechanisms have been proposed for the conversion of particle-bound chloride (Cl-) to gas-phase Cl2, the detailed processes involved remain uncertain.

Shipping is one of the most fuel-efficient ways to move freight, but the industry still produces significant greenhouse-gas emissions, including more than a quarter of the world's nitrogen oxides emissions. And it also produces more sulphur dioxide emissions than all land transportation combined. In the latest of Nature's our Future Transport series, Duncan Graham-Rowe looks at the new wave in shipping.

Dinitrogen (N2) fixation is widely recognized as an important process in controlling ecosystem responses to global environmental change, both today and in the past; however, significant discrepancies exist between theory and observations of patterns of N2 fixation across major sectors of the land biosphere.