A New All Season Passive Sampling System for Monitoring Ozone in Air

A new all season passive sampling system for monitoring O₃ in the atmosphere has been developed in the laboratory and validated in the field. The unique features for this system include a newly designed passive sampler and a rain shelter, which allow the passive sampler to be installed in the field facing downwards. An equation associated with meteorological parameters is used to calculate the passive sampling rates. This system has been extensively tested in the lab (temperature from –18 to 20°C, relative humidity from 13 to 81%, and wind speed from 0.5 to 150 cm/s) and validated in the field in climates of all seasons. The accuracy of the ozone concentrations in the atmosphere obtained with the use of the new passive sampling system was higher than 85% compared to those obtained with continuous ozone analyzers. The new ozone passive sampling system can be used to measure ambient O₃ concentrations ranging from 3 ppb to 1000 ppb based on one-day exposure and 0.1 ppb to 140 ppb for a monthly exposure period. It is also reasonable to conclude that the new passive sampling system can be used for eight-hour exposure study because of the low field blanks and high sampling rates.     

Monitoring human impacts on sandy shore ecosystems: a test of ghost crabs (Ocypode spp.) as biological indicators on an urban beach

This study evaluated the spatial and temporal distribution of metals in the coral reef system Cayos Arcas and Triangulos in the Campeche Bank region, off the Yucatan peninsula in Mexico. No information has been generated before for the incorporation of natural and non-natural occurring metals, some of which are possibly endowed by the oil marine station Cayo Arcas. The multivariate exploratory study of the metals on the coral skeletons, showed the formation of two distinct groups. The metals that have the highest influence on the differentiation of the groups are the metals that are natural constituents of the coral skeletons, in particular Sr can explain much of the differences between the groups, and to a much lesser extent are the metals that could be indicators of pollution. This differentiation suggests that, in our case, the environment around the corals has a higher impact than the non-naturally occurring metals (and possible indicators of pollution). The two groups formed corresponded to: the coral cores influenced by open sea variables and the coral cores in the inner part of the keys which is less exposed to open sea variables. A chronological study was made to two samples that had the longest coral section and were situated in two clearly distinctive zones: an exposed surface subjected to high wave forces and another that was less exposed. Ni and Zn show an accumulation trend in both coral samples, while Ba showed an increase in incorporation around 1980 when the Cayo Arcas oil marine station was constructed.     

A glimpse at short-term controls of evapotranspiration along the southern slopes of Kilimanjaro

Future climate characteristics of the southern Kilimanjaro region, Tanzania, are mainly determined by local land-use and global climate change. Reinforcing increasing dryness throughout the twentieth century, ongoing land transformation processes emphasize the need for a proper understanding of the regional-scale water budget and possible implications on related ecosystem functioning and services. Here, we present an analysis of scintillometer-based evapotranspiration (ET) covering seven distinct habitat types across a massive climate gradient from the colline savanna woodlands to the upper-mountain Helichrysum zone (940 to 3960 m.a.s.l.). Random forest-based mean variable importance indicates an outstanding significance of net radiation (R _net) on the observed ET across all elevation levels. Accordingly, topography and frequent cloud/fog events have a dampening effect at high elevations, whereas no such constraints affect the energy and moisture-rich submontane coffee/grassland level. By contrast, long-term moisture availability is likely to impose restrictions upon evapotranspirative net water loss in savanna, which particularly applies to the pronounced dry season. At plot scale, ET can thereby be approximated reasonably using R _net, soil heat flux, and to a lesser degree, vapor pressure deficit and rainfall as predictor variables (R ² 0.59 to 1.00). While multivariate regression based on pooled meteorological data from all plots proves itself useful for predicting hourly ET rates across a broader range of ecosystems (R ² = 0.71), additional gains in explained variance can be achieved when vegetation characteristics as seen from the NDVI are considered (R ² = 0.87). To sum up, our results indicate that valuable insights into land cover-specific ET dynamics, including underlying drivers, may be derived even from explicitly short-term measurements in an ecologically highly diverse landscape.     

Modeling biodegradation and kinetics of glyphosate by artificial neural network

An artificial neural network (ANN) model was developed to simulate the biodegradation of herbicide glyphosate [2-(Phosphonomethylamino) acetic acid] in a solution with varying parameters pH, inoculum size and initial glyphosate concentration. The predictive ability of ANN model was also compared with Monod model. The result showed that ANN model was able to accurately predict the experimental results. A low ratio of self-inhibition and half saturation constants of Haldane equations (< 8) exhibited the inhibitory effect of glyphosate on bacteria growth. The value of K(i)/K(s) increased when the mixed inoculum size was increased from 10(4) to 10(6) bacteria/mL. It was found that the percentage of glyphosate degradation reached a maximum value of 99% at an optimum pH 6-7 while for pH values higher than 9 or lower than 4, no degradation was observed.     

A Comparative Study of Environmental Tobacco Smoke Particulate Mass Measurements in an Environmental Chamber

Particulate mass concentration measurements have been made on environmental tobacco smoke (ETS) for the purpose of assessing the relative accuracy of several measurement procedures. ETS over a range of concentrations was generated in an environmental chamber by three methods. Mass concentration was measured by a gravimetric/spectrophotometric collection procedure, piezoelectric particle mass monitors, two nephelometry-based mass monitors, and a particle counting and sizing system. Two-hour average mass concentrations were determined by each method for concentrations ranging from very low levels up to those achieved by smoking one entire cigarette in the chamber. Statistical comparisons were made among procedures employing the gravimetric filter measurement as the basis for comparison. One nephelometry-based procedure gave significantly higher and the other significantly lower values than the filter determination. In one case, a correction for the difference between the particle mass density of the calibrating aerosol and that of ETS brought the nephelometry-based procedure into reasonable agreement with the filter measurement, while for the other, the correction did not resolve the discrepancy between methods. Statistically significant differences between the responses of two supposedly identical piezoelectric mass monitors were found, as was some slight dependence of the nephelometry- based procedures on method of ETS generation. In summary, the results indicate that significant errors can be expected if the instruments studied are used “off the shelf,” even for ETS generated under controlled laboratory conditions. Caution should be employed in field measurements where numerous sources and types of particulate matter can be encountered.     

On the Determination of Odor Thresholds in Air Pollution Control—An Experimental Field Study on Flue Gases from Sulfate Cellulose Plants

From the hygienic point of view, not only the health hazards caused by air pollutants but also the odor from emitted flue gases should be reduced to a minimum. An effective control of the risk of odor at ground level presupposes knowledge of the source concentration of the odoriferous gas as well as its odor threshold. This threshold has to be estimated empirically, as the flue gases often contain a complex mixture of different odoriferous substances, the odor thresholds of which are in most cases unknown. For this purpose a method has been developed for estimating the odor thresholds of flue gases emitted, from different industrial processes. The method, afield method, is based on an exposure procedure, a number of subjects compare different concentrations of the flue gas with samples of fresh air and decide at what concentration the flue gas is no longer noticeable. The gas samples used are neither compressed, nor absorbed or heated before the exposure test. The method has been used in two studies on gases from Swedish sulfate cellulose plants. In order to estimate the effect on the odor threshold of different deodorizing measures, gas samples were taken not only from the stack but also from different phases in the production process. The results and a brief discussion on the practical applications of the method are given.     

Control of Malodors from Kraft Recovery Operations by Pyrolysis

The major source of malodorous emissions which emanate from kraft mills is the recovery furnace and its associated direct contact evaporator. The primary reasons for this problem are gross furnace overloading and/or inadequate design. Existing recovery furnaces are incapable of carrying out, to an acceptable degree of completion, the complex sequence of physical and chemical steps which describe combustion. These steps are evaporation, sublimination, pyrolysis, recombination, and oxidation. A simplified odor model is presented which establishes the constraints which must be placed on the combustion phase of the recovery operation if environmental concentrations of malodorous compounds are to be held below their respective threshold odor levels. The pyrolysis and recombination steps of combustion have been isolated for study because they encompass the reaction mechanisms responsible for malodorous compound production. The findings of the steady state pyrolysis study indicate that the optimization of pyrolysis appears to be a very desirable process technique for abating alodorous emissions from kraft mills. The comprehensive data obtained in the study has engendered the current design and construction efforts toward a pilot plant operation.