editorial
Measuring the Invisible
T
his thematic issue, “Atmospheric Analysis as Related to Climate Change”, contains a number of publications dealing with air analysis. Is this interesting for Analytical Chemistry readers? Air is a seemingly simple matrix for analysts, not appearing to offer wide opportunities for research, and of course, it’s been there a long time. In reality, airOeven in remote areasOexperiences an enormous dynamic range of trace gas composition, fueled by numerous volatile metabolites released from microbial communities and exhalations from plant leaves and by a continuously changing mega-brew of organic and inorganic compounds emitted by the industrialized world, all inhomogeneously stirred by time-dependent, rapidly changing meteorological situations. I just returned from a government-sponsored meeting in Hong Kong in support of theme-based research. Air quality was a prominent topic, and of course, analytical chemistry was quickly recognized as the key discipline, providing the needed environmental instrumentation and the characteristics of modern analytical measurements. Measurements of air composition have for centuries been conducted to determine environmental quality, and early last century, national and international standardization panels were founded to assure valid analytical data for policymakers. However, discontinuities in mapped air quality data for a given compound still occur upon crossing a European national border (and probably not only there) because the air monitoring networks aren’t synchronized by classical validation tools of metrology. The study of particles in air has a long history. P.-J. Coulier in 1875 described a simple optical instrument that by sudden water supersaturation in air under adiabatic expansion produced transiently visible ultrafine water aerosol particles in the nanometer and larger size range. Nowadays, from the basic works of Einstein, Millikan, Smoluchowski, and others in 1900⫺1920, we know a lot about the origin and fate of suspended nanomaterials. However, there are also substantial knowledge gaps about particles in air. In typical inside office air, we expect ⬃5000 aerosol particles per mL; considering that a human being inhales 6⫺10 m3 of air per day, each person is confronted with more than 1010 nanoparticles in that timeframe. Nature is clever and complex, so these nanoparticles are collections of species of very diverse chemical and physical natures. Though many may be individually homogeneous, some aren’t. For example, “nano-onions” are made by incomplete combustion situations that lead to structured nanoparticles with carbon cores surrounded by layers of subsequently condensed unburnt or newly synthesized organic compounds. In addition, the modern automotive industry seeks to produce so-called zero-emission cars and trucks by 2015. One strategy to reach this goal is to produce only readily oxidizable carbon nano-
10.1021/AC1023217 2010 AMERICAN CHEMICAL SOCIETY
Published on Web 09/13/2010
particles that are removed in a tailpipe after-treatment section. Therefore, the determination of nanocrystallinity needs fresh analytical tools. Fast measurements and corresponding air control technologies need to be emphasized to produce good public air hygiene. Considering that many chemical aerosol systems are thermally labile (e.g., ammonium nitrate aerosol decomposes at ⬎300 K in a reversible reaction into HNO3 and NH3), in situ measurements are required. Issues of aerosol detection limits are also formidable; a typical 20-nm aerosol nanoparticle has a mass of only a few attograms and may be composed of multiple condensation nuclei, posing a tremendous challenge to analyze its molecular composition. And this analysis should ideally be online, if possible... Also, mainly unsolved is the unambiguous detection and characterization of biological particles in air, especially viruses. Though military and safety agencies have initiated many attempts to develop effective countermeasures for population protection, analytical tools capable of first identifying and then quantifying such airborne biological matter remain still a dream. Finally, while we humans see poorly what is in air, Nature sees it better. Some of the complicated consequences of climate change deal with optical properties of air plus suspended matter that is often produced through solar photochemistry. Internal mixing of particles can have positive or negative effects on climate forcing (i.e., the factors driving climate shift). Only rough optical detection schemes have been published so far to characterize this subject. I hope the above pinpoints the often underestimated scientific discipline of colloid science linked with analytical chemistry. Enjoy reading this issue!
Editor* Chair for Analytical Chemistry Institute of Hydrochemistry Technische Universita¨t Mu¨nchen *Professors Reinhard Niessner and Royce Murray and Dr. Jennifer Griffiths are co-editors of this issue.
OCTOBER 1, 2010 / ANALYTICAL CHEMISTRY
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