Free tropospheric ozone production after deep convection of dispersing tropical urban plumes

Ozone generation is computed in a one-dimensional photochemistry code following convective redistribution of tropical urban effluent into the free troposphere. Simulations are run at several stages of pollutant dilution by surrounding surface air. A threshold boundary layer NO_x concentration of 300 pptv is established for significant production enhancements at upper levels. Areas defined by the 300 pptv level are examined in the Gaussian dispersion framework based on a wet season plume event observed in Amazonia. Pollution travels slowly in the sluggish winds of the equatorial trough. Daily storms are likely to interrupt the effluent while coverages are still on the order of few thousand square kilometers and NO_x concentrations are above the threshold. Dry season plume sizes are difficult to assess because local concentration data are scarce, but it is conceivable that the faster trade winds lead to a several fold extension.     

Contaminants of food

A scheme has been developed to rank 70 industrial organic chemicals in order of their priority for further study as potential contaminants of food. Numerical scales were developed for the following seven key criteria concerning environmental issues, food and toxicity:

-Production volume

-Pattern of usage

-Possible fate in the environment

-Likelihood of chemical entering the food chain

-Mechanism of entry into the food chain

-Persistence and accumulation in the food chain

-Toxicity.

Each chemical was assigned a score for the above criteria, which were combined to give an overall ranking for the chemicals. This scheme has been endorsed by the MAFF Steering Group on Chemical Aspects of Food Surveillance. It will be used in the assessment of relative priorities for further non-statutory surveillance for these contaminants in the UK food supply.     

Bromine in waste incineration partitioning and influence on metal volatilisation

INTENTION, GOAL, SCOPE, BACKGROUND: The halogen bromine is far less abundant than chlorine, but it can be found at high concentrations in special materials like flame retarded plastics. The fate and effects of Br in waste incineration are not well understood. It may have similar implications like Cl for the volatilisation of heavy metals and the formation of low volatile organic compounds. Due to its lower oxidation potential, there is a risk of formation of elementary Br2 in the offgas. OBJECTIVE: Co-combustion tests of different types of Br containing plastic waste materials (up to 22%) and MSW in the TAMARA pilot plant for waste incineration were conducted to investigate the Br partitioning and the influence of Br on metal volatilisation. METHODS: The Br inventory of the fuel mix was elevated to approx. 1 wt-%. All input and output mass flows of the furnace have been sampled and the partitioning of Cl, Br, S, and a number of heavy metals, has been calculated on the basis of closed mass balances. RESULTS AND DISCUSSION: Organically-bound Br was typically released to more than 90% into the raw gas. Elementary Br2 was detected at high Br levels. Its presence was always analysed when all SO2 in the raw gas was oxidised to SO3. Br enhances the volatilisation of metals like K, Zn, Cd, Sn, Sb, and Pb out of the fuel bed principally in the same way as Cl. The tests gave strong indication that the promoting influence of the halogens on metal volatilisation is more pronounced than that of the fuel bed temperature. The volatilised metals are condensated on the fly ashes and are discharged along with the filter ashes. CONCLUSIONS: As long as a surplus of SO2 is present in the raw gas no Br2 is formed. Although the halogen induced transfer out of the fuel bed causes high concentrations of volatile metals in the filter ashes, a recovery is not economically feasible for the time being. The volatilisation gives no rise to metal emission problems as long as efficient dedusting is achieved. RECOMMENDATION AND OUTLOOK: If there is a risk of Br2 formation, in wet scrubbing a reducing agent has to be added to the neutral scrubber for efficient abatement. Filter ashes should be disposed of in a way that enables access for recovery in the future. The exact volatilisation characteristics of the various metals have to be studied in future using specifically tailored experiments.     

Marine macroalgae in polar regions as natural sources for volatile organohalogens

Marine macroalgae species from the polar regions were investigated for their importance as natural sources of volatile halogenated compounds released into the biosphere. Several different halogenated C1 to C4 hydrocarbons were identified and their release rates determined. The compounds contained mainly bromine and iodine, and form was the dominant compound released. Although an annual atmospheric input of approximately 10(8)-10(10) g bromine and 10(7)-10(8) g iodine was calculated from the release rates, marine macroalgae are apparently not the major source on a global scale, as the release is up to four orders of magnitude lower than a presumed annual flow from the oceans. Despite this, macroalgae may be more important on a local scale due to their occurrence at a high biomass in the coastal regions. The present paper gives an overview about studies done on the release of volatile halocarbons by macroalgae from polar regions. Furthermore, the function of these compounds in the macroalgal metabolism is discussed.     

Monitoring for 2,4-residues in fish species resident in treated lakes in east-central Ontario 1977–80

Authorized use of 2,4-D by cottage owners in Buckhorn Lake for the years 1977 to 1980 ranged from 124 to 280 kg of active ingredient, annually. This would give predicted average water concentrations of 2 to 4 g L^–1 during the June–July period. However, higher residues were observed in the Lake. Between 1977 and 1980, 353 individual fish, of eight species, were caught for analysis in Buckhorn and Chemong lakes. These fish belonged to eight edible species. Twelve percent of the fish caught during the pre-treatment period (i.e. May), had detectable residues of 2,4-D. Mean residues by species and year ranged from <5 to 30 g kg^–1 2,4-D. In the early post-treatment period (i.e. July), 69% of fish caught had mean residues by species which ranged from <5 to 136 g kg^–1 2,4-D. In the late post-treatment period (i.e. October), 19% of fish caught by year had detectable residues of 2,4-D. Mean residues by species during this period ranged from <5 to 60 g kg^–1 2,4-D. While 15 (i.e. 4%) of the 353 fish and fish composites had 2,4-D above the maximum residue limit of 100 g kg^–1 only six were of edible size.     

Use of large enclosures for perturbation experiments in lentic ecosystems: A review

Available literature on use of field enclosures in freshwater and marine systems is reviewed to assess how accurately enclosures mimic ecological conditions and process rates occurring in adjacent open habitat. Among- and within-replicate variability of ecological parameters in field enclosures is compared to those in laboratory microcosms and open field habitat respectively. Results concerning the potential ecological effects and fate of pollutants indicate that perturbation studies using field enclosures can provide defensible data at the population and community levels over time periods of several months and spatial scales of tens of meters. The degree of ecological realism that can be achieved, however, is variable. Chronic effects of some pollutants may be difficult to separate from nonspecific effects due to enclosure. Determination of cause/effect pathways for observed toxicant impacts generally will require supplemental laboratory studies.Work conducted under Electric Power Research Institute, Palo Alto, CA, contract RP 1822-6.     

Speciation of nickel in Canadian subbituminous and bituminous feed coals, and their ash by-products

The nickel species in the feed coals and ash by-products from seven Canadian power plants (including one with a fluidized bed combuster) burning local subbituminous and bituminous coals with sulfur contents ranging from 0.22 to 3.6% have been examined using nickel XANES spectroscopy. XANES spectroscopy of Ni in coal and coal derived ash is complicated by a poor signal : noise ratio due to fluorescence of the much more abundant iron in the coal. Nevertheless, it has proved possible to show that the Ni environment in coals varies from largely oxidic species to mixtures of Ni-containing oxide and sulfide species. The nickel in one oxidized coal appears to be present as nickel sulfate. Nickel in all bottom and fly ash samples examined appears also to be present largely in oxygen anion environments. With the exception of one fly ash sample, for which the Ni exhibited spectral features similar to those for Ni(2+) in spinel or oxide phases, the nickel in the bottom and fly ash samples appears to exist largely as Ni(2+) in environments similar to those reported for Ni in silicate glasses. The data obtained indicate that the presence of potentially carcinogenic nickel sulfides in ash by-products from combustion of these coals is unlikely.     

Design and field application of an automated cartridge sampler for VOC concentration and flux measurements

One of the major limitations in advancing the understanding of tropospheric ozone and aerosol generation and developing strategies for their control is the technical ability to accurately measure volatile organic compounds (VOCs). This paper describes the design of a constant flow VOC sampler. The versatile sampler can be used for fully automated concentration and flux measurements of VOCs. The sampler incorporates a microprocessor control unit and provides highly accurate mass flow control and significant ease of operation. Sampling sequences can be programmed directly or by remote control through a PC. All important operational parameters necessary for a complete sampling audit trail are logged. Compact weatherproof housings and low power consumption allow operation at remote sites and locations which are sensitive to disturbances or have restricted access. Inner wetted surfaces of the sampler are constructed from non-contaminating materials that do not sorb or emit VOC, and thus permit the collection of representative samples even in environments with very low VOC concentrations. The cartridge magazine provides a maximum of 20 sequential cartridge samples, which allows for long-term air quality assessments. In the dual channel mode, two samples can be collected simultaneously through two independent sample loops, providing ten sequential sample pairs. This design allows the parallel collection of (a) quality assurance backup samples, (b) samples on two different types of cartridges/sorbents to allow a variety of analyses, or (c) differential samples for flux measurements using enclosure, aerodynamic profile, or relaxed eddy accumulation (REA) methods. Field applications including airplane profile measurements above a tropical rainforest area, as well as gradient and REA measurements over a mid-latitude mixed forest stand are described, and demonstrate the validity and flexibility of the system. In particular, the application of the VOC sampler as an integrated part of a REA system is emphasized.     

Effects of Disturbance on Nitrogen Export from Forested Lands of the Chesapeake Bay Watershed

The objective of this research project is to develop, test, validate, and demonstrate an analytical framework for assessing regional-scale forest disturbance in the mid-Atlantic region by linking forest disturbance and forest nitrogen export to surface waters at multiple spatial scales. It is hypothesized that excessive nitrogen (N) leakage (export) from forested watersheds is a potentially useful, integrative "indicator" of a negative change in forest function which occurs in synchrony with changes in forest structure and species composition. Our research focuses mainly on forest disturbance associated with recent defoliations by the gypsy moth larva (Lymantria dispar) at spatial scales ranging from small watersheds to the entire Chesapeake Bay watershed. An approach for assessing the magnitude of forest disturbance and its impact on surface water quality will be based on an empirical model relating forest N leakage and gypsy moth defoliation that will be calibrated using data from 25 intensively-monitored forested watersheds in the region and tested using data from more than 60 other forested watersheds in Virginia. Ultimately, the model will be extended to the region using spatially-extensive data describing: 1) the spatial distribution of dominant forest types in the mid-Atlantic region based on both remote sensing imagery and plot-scale vegetation data; 2) the spatial pattern of gypsy moth defoliation of forested areas from aerial mapping; and 3) measurements of dissolved N concentrations in streams from synoptic water quality surveys.