Environmental context. Aerosol water-soluble organic carbon is a complex mixture of thousands of organic compounds which may have a significant influence on the climate-relevant properties of atmospheric aerosols. Using ultrahigh resolution mass spectrometry, more than 4000 individual molecular formulas were identified in non-urban aerosol water-soluble organic carbon. A significant fraction of the assigned molecular formulas were matched to assigned molecular formulas of laboratory generated secondary organic aerosols.

Environmental context. Understanding the molecular composition and chemical transformations of organic aerosols during atmospheric aging is a major challenge in atmospheric chemistry. Ultra-high resolution mass spectrometry can provide detailed information on the molecular composition of organic aerosols. Aerosol samples collected in summer and winter at an urban site are characterised and compared in detail with respect to the elemental composition of their components, especially nitrogen- and sulfur-containing compounds, and are discussed with respect to atmospheric formation processes.

Environmental context. The effects of atmospheric fine particulate matter (aerosols) on climate and human health can be strongly influenced by the chemical transformations that the particles undergo in the atmosphere, but these ‘aging’ reactions are poorly understood. Here diesel exhaust particles are aged in the laboratory to better understand how they could evolve in the atmosphere, and subtle but unmistakable changes in their chemical composition are found. These results provide a more complete picture of the atmospheric evolution of aerosols for inclusion in atmospheric models.

Environmental context. As atmospheric CO₂ levels rise due to human activities, more of the gas dissolves in the oceans, increasing their acidity. The effect of these seawater changes on marine organisms is largely unknown. We examine the consequences of higher CO₂ levels on the production by plankton of dimethyl sulfide, a climatically active gas. We find that higher CO₂ levels leads to lower concentrations of dimethyl sulfide in the seawater, which has potentially important implications for the future climate.

Environmental context. The association of specific organic matter (OM) compounds with clay mineral surfaces is believed to protect these compounds from degradation and thus result in long-term protection in soil. The molecular-level composition of soil OM associated with soil fractions was measured and compared using solid-state ¹³C nuclear magnetic resonance (NMR) and solution-state ¹H NMR methods. Combining these methods allowed more detailed characterisation of OM associated with different soil fractions and will improve the understanding of OM dynamics in soil.

Environmental context. Perfluoroalkyl compounds are organic contaminants that exhibit strong resistance to chemical- and microbial-degradation. As partitioning between solid and aqueous phases is expected to control the transport of perfluoroalkyl compounds, we studied the molecular mechanisms of their adsorption–desorption at a representative Fe oxide surface using in situ molecular spectroscopy. The results provide valuable information on the types of bonds formed, and enable a better understanding of the transport and fate of these organic contaminants in natural environments.

Environmental context. Although arsenic occurs at high concentrations in many marine systems, the influencing factors are poorly understood. The arsenic content of sediments, detritus, suspended particles and organisms have been investigated from different trophic levels in an open seagrass ecosystem. Total arsenic concentrations and arsenic species were organism-specific and determined by a variety of factors including exposure, diet and the organism physiology.

Environmental context. In terrestrial environments, humic substances act as major sorbents for calcium, which is an essential nutrient for organisms. This study shows that calcium binding by terrestrial humic acids is strongly dependent on pH and ionic strength. The results indicate that calcium binding by humic acids is primarily controlled by electrostatic forces and specific binding to carboxylic groups.

Environmental context. Uptake of metal ions by plants is often predicted with equilibrium models, which assume that the rate limiting step is trans-membrane uptake of the metal in the roots rather than the transport of the metal ion towards the site of uptake. Evidence is given that uptake of cadmium by plants is under strong transport control at environmentally relevant concentrations, whereas nickel uptake borders between transport and plant control. This explains the lack of ion competition effects for Cd uptake, whereas both proton and Mg ions were found to compete with Ni uptake.