Energy & Fuels 2008, 22, 2869–2870
2869
Communication Other Side of Climate Change: Nanoparticle Emission Andrei P. Sommer,*,† Dan Zhu,† and Burkhard Jaeger‡ Nanobionic Laboratory, Institute of Micro and Nanomaterials, UniVersity of Ulm, 89081 Ulm, Germany, and Gardena, Hans Lorenser Strasse 40, 89079 Ulm, Germany ReceiVed May 8, 2008. ReVised Manuscript ReceiVed June 2, 2008 Cognition of global warming is presently largely restricted to the dramatic physical and chemical changes triggered by the elevated CO2 levels. Biological implications, for instance, a worldwide increase of tropical diseases, are never directly caused by the elevated CO2 levels but indirect effects of warming. CO2 emission is frequently associated with that of nanoparticles. Importantly, nanoparticles are directly implicated in all three processes related to climate change: physical and chemical changes and biological effects, such as cardiovascular disease. Fuel hungry megacities are particularly vulnerable here. Consequently, strategies designed to simultaneously reduce both CO2 levels and nanoparticle concentrations in urban areas should be welcomed by city planners. Climate change is currently the most important topic on Earth and now reality for governments, industry, and the scientific community. Whereas the projections of human effects on the climate system are still lacking the precision necessary to accurately predict future tendencies,1 the global dimension of the problem manifests itself in a variety of dramatic scenarios. From the economic point of view, climate change is a unique challenge and demands an urgent global response. The analysis must be global and deal with long time horizons. Current plans to colonize Mars emerge from anticipating the worst-case scenario that the change is irreversible. In fact, nobody knows for sure whether the problem is reversible or not. Even if it is reversible, nobody can really predict how long its normalization will take. There are several factors, making a prediction practically impossible. Natural factors, for instance, those related to the hydrological cycle are so complex that the actual models cannot predict any trend. Anthropogenic factors, including but not limited to CO2 emissions from rapidly growing industries in Asia, with an unprecedented demand for fossil fuel, are virtually unknown. Geoengineering, with plans to cool the planet by throwing megatons of sulfate into the stratosphere is regarded as a possible2 but not necessarily harmless response to the problem of warming.3 Until very recently, all of these aspects of climate change were vehemently discussed by scientists as well as in the media. It is thus surprising to realize that the intense discussions suddenly made place to an element of quiet. In view of the unprecedented dimension of the problem, its complexity, and the limitations of the predictive models, one might interpret the change in attitude as adaptive resignation. Importantly, the warming of our planet is only one facet of climate change. The Stern * To whom correspondence should be addressed. E-mail: andrei.sommer@ uni-ulm.de. † University of Ulm. ‡ Gardena. (1) Pielke, R. A., Jr. Nat. Geosci. 2008, 1, 206.
Review,4 at present the most comprehensive analysis of the climate change problem, describes the actual status without any cognitions,5 restricts itself to the CO2 issue, and avoids mentioning the carbonaceous nanoparticles from burning fuel, co-emitted with CO2 and predicted to cause long-lived clouds and thereby less rain.6 In a warmer world, such clouds are expected to offer ideal proliferation conditions to microorganisms living in them, a process which is likely to constitute a significant biohazard in the era of the anthropocene. However, for many of us, a warmer and possibly drier Earth might be too abstract, too big, and far from what we are used to as reality. Not so our own life expectation: Whereas statistics show that people live today longer, there is increasing observational evidence showing the opposite for those exposed to high levels of fine particulate air pollution from anthropogenic emissions,7–9 which always include nanoparticles. A recent study with model character compared equivalent pulmonary loads of fine and ultrafine TiO2 particles, suggesting that ultrafine TiO2 inhalation produces systemic microvascular effects.10 Potent motivation to urgently search for strategies to reduce nanoparticle concentrations in the air might emerge from their impact on aging. Normally, populations living in urban locations are exposed to the highest concentrations of fine particulate air pollution, including nanoparticles. Modern city planners have already responded to this burden by implementing green areas. For instance, web pages describing megacities of China regularly start by mentioning the green areas. Before political and social intervention will further encourage the development and use of cleaner sources of energy, Figure 1 might inspire an economical and immediately practicable approach, comprising two synergistic countermeasures: simultaneous reduction of CO2 and nanoparticle levels in the air by plants. Their contribution in reducing CO2 levels is clear, and their potential to reduce nanoparticle concentrations in the air follows from atomic force (2) Crutzen, P. J. Climate Change 2006, 77, 211–219. (3) Sommer, A. P. Cryst. Growth Des. 2007, 7, 1031–1034. (4) Stern, N. The Economics of Climate Change; HM Treasury: London, U.K., 2006. (5) Bode, S.; Stiller, S.; Wedemeier, J. Berenberg Bank, HWWI: Strategie 2030-Klimawandel, 2007. (6) Ramanathan, V.; Carmichael, G. Nat. Geosci. 2008, 1, 221–227. (7) Miller, K. A.; Siscovick, D. S.; Sheppard, L.; Shepherd, K.; Sullivan, J. H.; Anderson, G. L.; Kaufman, J. D. N. Engl. J. Med. 2007, 356, 447– 458. (8) Dominici, F.; Peng, R. D.; Bell, M. L.; Pham, L.; McDermott, A.; Zeger, S. L.; Samet, J. M. J. Am. Med. Assoc. 2006, 295, 1127–1134. (9) Eftim, S. E.; Samet, J. M.; Janes, H.; McDermott, A.; Dominici, F. Epidemiology 2008, 19, 209–216. (10) Nurkiewicz, T. R.; Porter, D. W.; Hubbs, A. F.; Cumpston, J. L.; Chen, B. T.; Frazer, D. G.; Castranova, V. Part. Fibre Toxicol. 2008, 5, 1–12.
10.1021/ef800324n CCC: $40.75 2008 American Chemical Society Published on Web 06/18/2008
2870 Energy & Fuels, Vol. 22, No. 4, 2008
Figure 1. Fuel combustion is associated with nanoparticles (NP) and CO2 emission. Intervention routes 1 and 2 signify possibilities of action that can be taken immediately. Plant leaves act as highly effective scavengers for nanoparticles specifically when moist and help consume CO2, thereby cleaning the air twice. The interplay between less rain and warming is a precondition for desertification. The photograph on the right shows large amounts of pollen (arrow) on wet leaves.
microscopy experiments, providing evidence for glue-like water layers on hydrophilic surfaces11 and the circumstance that nanoparticles originating from pollution sources are normally hydrophilic.12 Thus, in combination even with a minimum amount of humidity, plant leaves will act as efficient scavengers for airborne nanoparticles, in particular when not exposed to sunlight.13 Their ability to collect and bind even particles as large as pollen is documented in Figure 1. At higher temperatures, humidity in conjunction with leaves cools the air. Generally, the leaves of plants represent more active surface than the walls of buildings occupying an equal volume. Activity comprises the balanced interplay of three environmentally relevant functions: scavenging, self-cleaning, and cooling, perfected by nature over millions of years. Together with
properly selected plants arranged in walls, as suggested in the inset of Figure 1, sufficient rain or quantitatively and temporally optimized spray irrigation could simultaneously fulfill all three functions. Thus far, city planners have one criterion to select plants: ornamental value. Prospective city planning should consider the implementation of plants with leaves with a capacity to collect and bind nanoparticles. For the identification of the proper air-cleaning plants, we recommend detailed studies focusing on an optimum in the combination maximum CO2 conversion and nanoparticle capture, with the latter adjusted to the humidity levels prevailing locally. Lower humidity levels should favor plant leaves with a tendency toward hydrophilic. Higher humidity levels should permit to exploit the self-cleaning capacity of superhydrophobic leaves.14
(11) Jinesh, K. B.; Frenken, J. W. M. Phys. ReV. Lett. 2006, 96, 166103. (12) Sommer, A. P. Cryst. Growth Des. 2006, 6, 749–754. (13) Sommer, A. P.; Caron, A.; Fecht, H. J. Langmuir 2008, 24, 635– 636.
EF800324N (14) Bhushan, B.; Jung, Y. C. Nanotechnology 2006, 17, 2758–2772.
