The transformation of outdoor ammonium nitrate aerosols in the indoor environment

Recent studies associate particulate air pollution with adverse health effects; however, the exposure to indoor particles of outdoor origin is not well characterized, particularly for individual chemical species. We conducted a field study in an unoccupied, single-story residence in Clovis, California to provide data and analyses to address issues important for assessing exposure. We used real-time particle monitors both outdoors and indoors to quantify nitrate, sulfate, and carbon particulate matter of particle size 2.5 μm or less in diameter (PM-2.5). The results show that measured indoor ammonium nitrate concentrations were significantly lower than would be expected based solely on penetration and deposition losses. The additional reduction can be attributed to the transformation indoors of ammonium nitrate into ammonia and nitric acid gases, which are subsequently lost by deposition and sorption to indoor surfaces. A mass balance model that accounts for the kinetics of ammonium nitrate evaporation was able to reproduce measured indoor ammonium nitrate and nitric acid concentrations, resulting in a fitted value of the deposition velocity for nitric acid of 0.56 cm s⁻¹. The results indicate that indoor exposure to outdoor ammonium nitrate in Central Valley of California are small, and suggest that exposure assessments based on total particle mass measured outdoors may obscure the actual causal relationships for indoor exposure to particles of outdoor origin.     

Considering science needs to deliver actionable science

Conservation practitioners, natural resource managers, and environmental stewards often seek out scientific contributions to inform decision-making. This body of science only becomes actionable when motivated by decision makers considering alternative courses of action. Many in the science community equate addressing stakeholder science needs with delivering actionable science. However, not all efforts to address science needs deliver actionable science, suggesting that the synonymous use of these two constructs (delivering actionable science and addressing science needs) is not trivial. This can be the case when such needs are conveyed by people who neglect decision makers responsible for articulating a priority management concern and for specifying how the anticipated scientific information will aid the decision-making process. We argue that the actors responsible for articulating these science needs and the process used to identify them are decisive factors in the ability to deliver actionable science, stressing the importance of examining the provenance and the determination of science needs. Guided by a desire to enhance communication and cross-literacy between scientists and decision makers, we identified categories of actors who may inappropriately declare science needs (e.g., applied scientists with and without regulatory affiliation, external influencers, reluctant decision makers, agents in place of decision makers, and boundary organization representatives). We also emphasize the importance of, and general approach to, undertaking needs assessments or gap analyses as a means to identify priority science needs. We conclude that basic stipulations to legitimize actionable science, such as the declaration of decisions of interest that motivate science needs and using a robust process to identify priority information gaps, are not always satisfied and require verification. To alleviate these shortcomings, we formulated practical suggestions for consideration by applied scientists, decision makers, research funding entities, and boundary organizations to help foster conditions that lead to science output being truly actionable.     

Physical resuspension and vertical mixing of sediments on a high energy continental margin (Sydney, Australia)

Four sediment cores from the continental margin adjacent to Sydney were analyzed for 210Pb, 137Cs, trace metals (Ag, Cd, Co, Cu, Mn, Ni, Pb, Zn), iron, dry bulk density, mud and moisture content. The concentrations of trace metals in the total sediment are low at all sites, although slightly elevated concentrations of Ag, Cu, Pb and Zn are present in the fine fraction of sediment (< 62.5 microns) near a major ocean outfall. Concentrations of trace metals in the fine fraction of sediment are similar in the upper 10-15 cm, indicating strong vertical mixing of the sediments, whereas an upward coarsening grain size in the upper 1-3 cm of sediment supports physical resuspension during storms. Sediment accumulation rates on the middle shelf adjacent to Sydney were estimated from downcore profiles of 210Pb and 137Cs and range between 0.2 and 0.4 cm yr-1. Although the mass fluxes of Cu, Pb and Zn within a distance of 2 km from the outfall (up to 36.1, 30.8 and 86.2 micrograms cm-2 yr-1, respectively) are greater than 20 km north of the outfall (< 23.5 micrograms cm-2 yr-1), the low concentrations of trace metals in sediments near the outfall support an efficient dispersal of anthropogenic contaminants on this continental margin.     

Migration of pollutants in groundwater: I. reduction of numerical dispersion by conformal mapping

The partial differential equations governing the migration of adsorbable pollutants undergoing 2-dimensional flow in saturated aquifers are presented. The analytical solution of these equations is rarely possible, and the use of mesh or grid techniques for numerical integration leads to so-called numerical dispersion, excessive dispersion which is an artifact associated with the numerical method. We discuss here the use of conformal mapping techniques to develop coordinate systems in which numerical dispersion transverse to the direction of flow is eliminated. Some simple illustrations are presented.     

Dioxin and dibenzofuran concentrations in blood of a general population from Tarragona, Spain

The concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were determined in plasma samples of 20 nonoccupationally exposed subjects living in the vicinity of a new hazardous waste incinerator (HWI), now under construction in Tarragona (Catalonia, Spain). The mean PCDD/F value was 27.0 pg I-TEQ/g lipid with a range from 14.8 to 48.9 pg I-TEQ/g lipid. All samples showed higher PCDD than PCDF levels. Although PCDD/F concentrations were higher in women (27.7 pg I-TEQ/g lipid) than in men (25.2 pg I-TEQ/g lipid), the difference was not statistically significant. While a significant correlation (r = 0.565, p < 0.01) between the age of the subjects and the levels of PCDD/F in plasma could be observed, no significant differences were found in relation to the specific residential area. The plasma concentrations of PCDD/F obtained in the current study are discussed and compared with the results of similar investigations reported in the last two years.