Major Atmospheric Source Research Articles

Environmental photochemistry on plants: recent advances and new opportunities for interdisciplinary research.

Plants play a central role in the photochemistry of chemicals in the environment. They represent a major atmospheric source of volatile organic compounds (VOCs) but also an important environmental surface for the deposition and photochemical reactions of pesticides, gaseous and particulate pollutants. In this review, we point out the role of plant leaves in these processes, as a support affecting the reactions physically and chemically and as a partner through the release of natural constituents (water, secondary metabolites). We discuss the influence of the chosen support (leaves, needle surfaces or fruit cuticles, extracted cuticular waxes and model surfaces) and other factors (additives, pesticides mixture, and secondary metabolites) on the photochemical degradation kinetics and mechanisms. We also show how plants can be a source of photochemically reactive species which can act as photosensitizers promoting the photodegradation of pesticides or the formation and aging of secondary organic aerosols (SOA) and secondary organic materials (SOM). Understanding the fate of chemicals on plants is a research area located at the interface between photochemistry, analytical chemistry, atmospheric chemistry, microbiology and vegetal physiology. Pluridisciplinary approaches are needed to deeply understand these complex phenomena in a comprehensive way. To overcome this challenge, we summarize future research directions which have been clearly overlooked until now.

Methods in plant foliar volatile organic compounds research.

Plants are a major atmospheric source of volatile organic compounds (VOCs). These secondary metabolic products protect plants from high-temperature stress, mediate in plant–plant and plant–insect communication, and affect our climate globally. The main challenges in plant foliar VOC research are accurate sampling, the inherent reactivity of some VOC compounds that makes them hard to detect directly, and their low concentrations. Plant VOC research relies on analytical techniques for trace gas analysis, usually based on gas chromatography and soft chemical ionization mass spectrometry. Until now, these techniques (especially the latter one) have been developed and used primarily by physicists and analytical scientists, who have used them in a wide range of scientific research areas (e.g., aroma, disease biomarkers, hazardous compound detection, atmospheric chemistry). The interdisciplinary nature of plant foliar VOC research has recently attracted the attention of biologists, bringing them into the field of applied environmental analytical sciences. In this paper, we review the sampling methods and available analytical techniques used in plant foliar VOC research to provide a comprehensive resource that will allow biologists moving into the field to choose the most appropriate approach for their studies.

Surface ocean iron fertilization: The role of airborne volcanic ash from subduction zone and hot spot volcanoes and related iron fluxes into the Pacific Ocean

Surface ocean iron (Fe) fertilization can affect the marine primary productivity (MPP), thereby impacting on CO2 exchanges at the atmosphere-ocean interface and eventually on climate. Mineral (aeolian or desert) dust is known to be a major atmospheric source for the surface ocean biogeochemical iron cycle, but the significance of volcanic ash is poorly constrained. We present the results of geochemical experiments aimed at determining the rapid release of Fe upon contact of pristine volcanic ash with seawater, mimicking their dry deposition into the surface ocean. Our data show that volcanic ash from both subduction zone and hot spot volcanoes (n = 44 samples) rapidly mobilized significant amounts of soluble Fe into seawater (35–340 nmol/g ash), with a suggested global mean of 200 ± 50 nmol Fe/g ash. These values are comparable to the range for desert dust in experiments at seawater pH (10–125 nmol Fe/g dust) presented in the literature (Guieu et al., 1996; Spokes et al., 1996). Combining our new Fe release data with the calculated ash flux from a selected major eruption into the ocean as a case study demonstrates that single volcanic eruptions have the potential to significantly increase the surface ocean Fe concentration within an ash fallout area. We also constrain the long-term (millennial-scale) airborne volcanic ash and mineral dust Fe flux into the Pacific Ocean by merging the Fe release data with geological flux estimates. These show that the input of volcanic ash into the Pacific Ocean (128–221 × 1015 g/ka) is within the same order of magnitude as the mineral dust input (39–519 × 1015 g/ka) (Mahowald et al., 2005). From the similarity in both Fe release and particle flux follows that the flux of soluble Fe related to the dry deposition of volcanic ash (3–75 × 109 mol/ka) is comparable to that of mineral dust (1–65 × 109 mol/ka). Our study therefore suggests that airborne volcanic ash is an important but hitherto underestimated atmospheric source for the Pacific surface ocean biogeochemical iron cycle.

The excitation of ducted modes by passing internal waves

A local peak in the atmospheric wind or stability profile supports ducted (vertically trapped) modes. If the duct is rather high in the atmosphere it cannot be directly excited by the major atmospheric sources such as convection, but an internal gravity wave radiating out of such sources transfers energy to the duct via nonlinear processes related to the resonance triad interaction. The amplitude of such a transfer is computed. The modal excitations remain after the internal wave has left the region, and while each passing wave adds only a small amount of activity to the duct such contributions are cumulative and drive the modal activity up to a level where it is limited by local dissipation. This suggests the possibility of monitoring the mean flux of internal waves through the region by measuring activity within elevated ducts, a procedure that offers several advantages over monitoring the wave flux directly.

Methane fluxes in the southern North Sea: the role of European rivers

Methane distributions were measured in the Southern Bight of the North Sea during March 1989 as part of the North Sea Program of the United Kingdom Natural Environment Research Council. Methane concentrations in the open North Sea were at or near solubility equilibrium with the atmosphere, but near the coast of the Netherlands, in the plume of the Rhine, extremely high methane values (as high as 120 times saturation) were observed. Both the Rhine and Scheldt rivers, and possibly coastal sediments, seemed to be significant regional sources of methane. Methane oxidation represented a relatively small sink for methane in the North Sea compared to gas loss to the atmosphere. This was due, in part, to the fact that methane oxidizing bacteria within the river plume appeared to be oxidizing the gas at close to their maximal rate, although offshore bacteria were able to increase oxidation rates as methane concentrations increased. Thus our studies suggested that bacterial methane oxidation kinetics were saturated at much lower methane concentrations in plume or estuarine waters than in open ocean situations. If the Rhine and Scheldt are the sources of the methane found in the Southern Bight, river concentrations of methane must be high (order of 50–5000 nM). Although rivers and coastal zones may not represent a major atmospheric source of methane, they can be very important as methane sources to the coastal ocean.

The quantities of cadmium, lead, mercury and arsenic entering the U.K. environment from human activities

This paper presents an estimate of the quantities of cadmium, lead, mercury and arsenic entering the U.K. environment from human activities. Discharges are divided into three source categories: the production and use of the elements, inadvertent sources and various waste disposal practices. The major atmospheric sources of cadmium and mercury include refuse incineration, non-ferrous metal production, iron and steel production, fossil fuel combustion and, for mercury alone, the chlor-alkali industry. In contrast, lead and arsenic each have only one major atmospheric source: petrol and coal combustion, respectively. The largest inputs of cadmium, lead and mercury to landfill arise from the disposal of municipal wastes; for arsenic, ash disposal from coal combustion is more important. Industrial activities represent the major sources of trace element input to the U.K. sewage system but domestic sources are important for lead and cadmium, while road run-off makes a considerable lead input. In U.K. coastal waters the major sources of cadmium are the direct discharge of sewage and industrial effluents. For the other elements, the dumping of solid wastes is of more significance. The largest inputs of lead, mercury and arsenic to U.K. agricultural land arise from atmospheric deposition; for cadmium the application of phosphate fertilizers is a more important source, while sewage sludge can be of local significance.