Kinetics of OH radical reactions with dibenzo-p-dioxin and selected chlorinated dibenzo-p-dioxins

The pulsed laser photolysis/pulsed laser-induced fluorescence (PLP/PLIF) technique has been applied to obtain rate coefficients for OH + dioxin (DD) (k1), OH + 2-chlorodibenzo-p-dioxin (2-CDD) (k2), OH + 2,3-dichlorodibenzo-p-dioxin (2,3-DCDD) (k3), OH + 2,7-dichlorodibenzo-p-dioxin (2,7-DCDD) (k4), OH + 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD) (k5), OH + 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD) (k6), and OH + octachlorodibenzo-p-dioxin (OCDD) (k7) over an extended range of temperature. The atmospheric pressure (740 +/- 10 Torr) rate measurements are characterized by the following Arrhenius parameters (in units of cm3 molecule(-1) s(-1), error limits are 1 omega): k1(326-907 K) = (1.70+/-0.22) x 10(-12)exp(979+/-55)/T, k2(346-905 K) = (2.79+/-0.27) x 10(-12)exp(784+/-54)/T, k3(400-927 K) = 10(-12)exp(742+/-67)/T, k4(390-769 K) = (1.10+/-0.10) x 10(-12)exp(569+/-53)/T, k5(379-931 K) = (1.02+/-0.10) x 10(-12)exp(580+/-68)/T, k6(409-936 K) = (1.66+/-0.38) x 10(-12)exp(713+/-114)/T, k7(514-928 K) = (3.18+/-0.54) x 10(-12)exp(-667+/-115)/T. The overall uncertainty in the measurements, taking into account systematic errors dominated by uncertainty in the substrate reactor concentration, range from a factor of 2 for DD, 2-CDD, 2,3-DCDD, 2,7-DCDD, and 2,8-DCDD to +/- a factor of 4 for 1,2,3,4-TCDD and OCDD. Negative activation energies characteristic of an OH addition mechanism were observed for k1-k6. k7 exhibited a positive activation energy. Cl substitution was found to reduce OH reactivity, as observed in prior studies at lower temperatures. At elevated temperatures (500 K < T < 500 K), there was no experimental evidence for a change in reaction mechanism from OH addition to H abstraction. Theoretical calculations suggest that H abstraction will dominate OH reactivity for most if not all dioxins (excluding OCDD) at combustion temperatures (>1000 K). For OCDD, the dominant reaction mechanism at all temperatures is OH addition followed by Cl elimination.     

Formation and inhibition of chloroaromatic micropollutants formed in incineration processes

The formation pathways for chlorinated aliphatic and chlorinated aromatic compounds in technical incineration processes are reviewed. It is shown that acetylene is converted to chloroaromatic compounds including PCDD/F in a special flow reactor by catalytic activity of CuCl2 in the temperature regime of a post-combustion zone of technical incinerators. Mechanistic pathways begin with chlorination of acetylene. Dichloroacetylene is further condensed to C-4 and C-6 units. Hexachlorobenzene is the dominant aromatic compound and a likely precursor to chlorinated phenols and PCDD/F. Two specific mechanisms of formation of chlorinated aromatic compounds including PCDD/F have been advanced. Both mechanisms begin with the formation of dichloroacetylene from flame pyrolysis products like acetylene. Condensation of dichloroacetylene is mediated by copper species via metallacyclic intermediates and/or a catalytic cycle involving copper stabilized trichlorovinyl radicals. The final pathways of conversion of chlorinated benzenes to PCDD/F via chlorophenols are under active investigation.     

Particulate matter in California: part 1--Intercomparison of several PM2.5, PM10-2.5, and PM10 monitoring networks

It will be many years before the recently deployed network of fine particulate matter with an aerodynamic diameter less than 2.5 microm (PM2.5) Federal Reference Method (FRM) samplers produces information on nonattainment areas, trends, and source impacts. However, data on PM2.5 and its major constituents have been routinely collected in California for the past 20 years. The California Air Resources Board operated as many as 20 dichotomous (dichot) samplers for PM2.5 and coarse PM (PM10-2.5). The California Acid Deposition Monitoring Program (CADMP) collected 12-h-average PM2.5 and PM10 from 1988 to 1995 at ten urban and rural sites and 24-h-average PM2.5 at five urban sites since 1995. Beginning in 1994, the Children's Health Study collected 2-week averages of PM2.5 in 12 communities in southern California using the Two-Week Sampler (TWS). Comparisons of collocated samples establish relationships between the dichot, CADMP, and TWS samplers and the 82-site network of PM2.5 FRM samplers deployed since 1999 in California. PM mass data from the different monitoring programs have modest to high correlation to FRM mass data, fairly small systematic biases and negative proportional biases ranging from 7 to 22%. If the biases are taken into account, all of the programs should be considered comparable with the FRM program. Thus, historical data can be used to develop long-term PM trends in California.     

Patterns of growth,energy utilization and reproduction in some meso- and bathypelagic fishes off Southern California

We have studied growth, energy use and reproduction in 4 mesopelagic fishes and 5 bathypelagic fishes living off Southern California (USA). All of the mesopelagic species underwent diurnal vertical migrations, while none of the bathypelagic species did so. The life histories of these pelagic fishes were compared among themselves and with epipelagic sardines and anchovies studied by others. The epipelagic species had the highest growth rates (estimated from otoliths, expressed in standard length or kilocalories), the mesopelagic species had the lowest growth rates and the bathypelagic species had intermediate growth rates. The relatively rapid growth rates of the bathypelagic fishes were achieved by high relative growth efficiencies made possible by low metabolic rates. Of the species studied, the lifespans of the epipelagic and bathypelagic species ranged from 4 to 8 yr and the lifespans of mesopelagic species from 5 to 8 yr. Data on egg diameters suggest that the mesopelagic species first reproduce in their 3rd yr, while the bathypelagic species do so in their last year. Epipelagic fishes generally have a large size, rapid growth, long life and early, repeated reproduction. Mesopelagic fishes are characterized by small size, slow growth, long life and early, repeated reproduction. Bathypelagic fishes generally have large size, rapid growth, somewhat shorter lives and late reproduction, which is possible a single event. The latter pattern is evidently feasible only in a rather stable environment where juvenile survivorship would always display relatively low variability. Many unusual characteristics of deep-living animals have possibly been selected by factors peculiar to the environment; however, such characteristics are just as likely to have been selected by factors equally present in many other environments, but not expressed there due to masking selective forces. In particular, we have in mind the darkness, stability and homogeneity of the bathypelagic realm as phenomena which represent the effective absence of many selective forces.The first two authors contributed equally and their names are listed in alphabetical order     

Uptake and release of phosphorus by phytoplankton in the Chesapeake Bay estuary,USA

The phytoplankton uptake and release rates for inorganic phosphate, dissolved organic phosphate and polyphosphate were estimated during 5 cruises on the Chesapeake Bay over a 9-month period. Phosphorus in all pools turned over in several minutes to 100 h, and each soluble pool appeared to contain fractions which were metabolically useful to the phytoplankton. Maximal uptake rates (V _m ) for orthophosphate ranged from 0.02 to 2.95 μg-at P (1.h)^-1 with half saturation constants (K _s ) between 0.09 and 1.72 μg-at P l^-1. At low soluble reactive phosphorus concentrations, the uptake rate of trace ³²P orthophosphate was initially rapid, but declined after 15 to 60 min incubation. The data suggest that the initial uptake phase was dominated by exchange of ³²PO₄ ^≡ for ³¹PO₄ ^≡ in the membrane transport systems whereas the subsequent phase represented the net incorporation of orthophosphate into phytoplankton cells.     

Contaminant Concentrations in the Atmosphere of Los Angeles County

Sampling for nitrogen and sulfur dioxides was initiated at several National Air Sampling Network stations in 1959 using a sampler developed for that purpose. In 1961 the Gas Sampling Network was expanded to its maximum of 49 stations. Sampling equipment and collecting solutions are supplied and chemical analyses performed by the network laboratories. Sampling and analysis procedures are described briefly. Average and maximum 24-hour concentrations of nitrogen dioxide and sulfur dioxide observed at 48 stations during 1961-1963 are presented.     

Schedule of Technical Sessions

Peroxyacyl nitrates are a family of compounds which result from photochemical reactions between contaminants released to the atmosphere by combustion of organic fuels. Peroxyacetyl nitrate (PAN) is the most abundant member of this family and is responsible for serious plant injury in some polluted areas. Plant injury has been recognized in at least 19 states and several foreign countries but economic loss has caused greatest concern in California. Characteristically, injury from PAN appears as glazing or bronzing of the lower leaf surface but the symptom syndrome may also include tissue collapse, chlorosis, and leaf drop. PAN inhibits activity of several enzyme systems by attacking the sulfhydryl group when enzyme extracts are fumigated in vitro, PAN may produce visible symptoms when sensitive plants are exposed for 4 hours to about 14 ppb. Other chemical members of the family are more toxic than PAN. Concentrations of 20 to 30 ppb PAN occur frequently at Riverside, Calif, and a maximum peak of 58 ppb was measured for one 2-hour period. Peaks as high as 54 ppb were reported at Salt Lake City, and 210 ppb at Los Angeles, Calif.