Research▼Watch Oceanic uptake of CO2 Most ocean general circulation models overestimate how much anthropogenic CO2 oceans have accumulated over the past two decades, according to new estimates based on the global chlorofluorocarbon (CFC) data set. The findings suggest that the oceans may not be as large of a sink for CO2 as previously thought. Although CFC concentrations cannot be used directly to infer anthropogenic CO2 uptake by the oceans, they do provide information about the “age” of a water mass, which is defined as the amount of time since the water was in contact with the atmosphere. Ben McNeil of Princeton University and colleagues used existing data on CFCs to estimate water ages and combined that information with historical atmospheric CO2 levels and equations on carbonate chemistry equilibrium to estimate dissolved inorganic carbon concentrations over the past 20 years. According to their results, the oceans took up a maximum of 1.9 petagrams of carbon per year from mid-1980 to mid-1989 and 2.3 petagrams of carbon per year from mid1990 to mid-1999. Only 3 of 12 international models that simulate anthropogenic CO2 uptake were close to this upper limit. (Science 2003, 299, 235–239)
Pesticides on particles Researchers at the University of California–Riverside have developed an analytical method to detect pesticide residues on single particles. The new approach could be used to study the partitioning and distribution of pesticides in the atmosphere immediately following their application. Pesticide residues find their way into the atmosphere through multiple pathways, including direct spray drift, volatilization from soil, and wind erosion of contaminated soils. Once in the air, they can be transported over
long distances, particularly in areas with extensive, heavy fog. Using a real-time technique called aerosol time-of-flight mass spectrometry (ATOFMS), Jeffrey R. Whiteaker and Kimberly A. Prather analyzed individual particles that were generated in the laboratory from standard solutions of commonly used pesticides and from pesticide-coated soils. The MS spectra of the pesticidecontaining particles had distinct mass fragments that could be used as markers for identifying pesticides in airborne particles. In addition, the analysis provided information on the chemicals associated with the pesticides in the particles, allowing the researchers to identify specific particle types containing pesticides. Such information could be used to determine the source of a pesticide and how it has been transformed in the atmosphere. (Anal. Chem. 2003, 75, 49–56)
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Sprawl threatens biodiversity Urban sprawl, not population growth, is the real threat to biodiversity, according to a study by researchers at Michigan State and Stanford Universities. A worldwide analysis of the growth rate in households found dramatic increases in biodiversity “hotspots”—regions rich in species that are being endangered by human activities—even in places with declining birth rates. This trend means that fewer people live in the average home than in the past, and this has led to more land and resources being used to support the same population. The findings support those arguing for “smart growth” initiatives that limit development in rural areas and encourage investment in cities and urban regions. However, as the authors point out, social factors such as higher per capita income, lower fertility rates, increasing divorce rates, aging populations, and fewer multigenerational family homes are driving this trend, and these are harder to control. Moreover, critics of smart
growth claim that these laws limit the number of affordable homes, which particularly affects lower-income families. The study, which was headed by Jianguo Liu, reports that in hotspot countries, household numbers grew on average 3.1% between 1985 and 2000, and this far outstripped the average 1.8% population increase. If household numbers had remained the same, 155 million fewer homes would have been needed during those years. Nonhotspot countries, on the other hand, had a more modest 1.7% growth in households, which roughly matched the population increase. Overall, the authors expect that household size in hotspot countries will drop from an average of 4.7 people in 1985 to 3.4 by 2015, which will require another 233 million homes in these increasingly crowded areas between 2000 and 2015. (Nature 2003, DOI 10.1038/nature01359)
MARCH 1, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 91 A
