ionization potentials, electron affinities, and charge distribution, and that of Mulliken,25 which is related to ionization potentials and electron affinities. None provides a linear free energy relationship for the reactions under discussion here. Typically, the enhancement of the rate constant caused by CH3 substitution is underestimated compared to the predicted reduction of reactivity caused by the substitution of the electron-withdrawing halogen atoms.The reaction transition state in the R + HI reactions, whether formed directly from the reactants or formed from a rearrangement of an R.1-H complex,' involves an H atom with a partial positive charge located in the region between the I atom and the methyl radical. Enhanced electron density (as provided by methyl (25) Mullikcn, R. S. J . Chem. Phys. 1934, 2, 782.substitution for H) at the methyl radical carbon would stabilize such a transition state and facilitate reaction, while diminished electron density (such as that caused by halogen atom substitution for H) would destabilize such a transition state. This is the behavior that is observed.Additional studies of the kinetics of R + HI and R + HBr reactions are in progress to understand more fully the factors controlling reactivity. Acknowledgment.The kinetics and mechanism of the sonochemical reactions of p-nitrophenol have been investigated in oxygenated aqueous solutions. In the presence of ultrasound (20 W z , 84 W) pnitrophenol was degraded primarily by denitration to yield NO2-, NOf, benzoquinone, hydroquinone, 4nitrocatecho1, formate, and oxalate. These reaction products and the kinetic observations are consistent with a model involving high-temperature reactions of pnitrophenol in the interfacial region of cavitation bubbles. The main reaction pathway appears to be carbon-nitrogen bond cleavage. Reaction with hydroxyl radical provides a secondary reaction channel. The average effective temperature of the interfacial region surrounding the cavitation bubbles was estimated to be T 800 K.

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The number of ultrafine particles may be a more health relevant characteristic of ambient particulate matter than the conventionally measured mass. Epidemiological time series studies typically use a central site to characterize human exposure to outdoor air pollution. There is currently very limited information how well measurements at a central site reflect temporal and spatial variation across an urban area for particle number concentrations (PNC). The main objective of the study was to assess the spatial variation of PNC compared to the mass concentration of particles with diameter less than 10 or 2.5 mm (PM 10 and PM 2.5). Continuous measurements of PM 10 , PM 2.5 , PNC and soot concentrations were conducted at a central site during October 2002-March 2004 in four cities spread over Europe (Amsterdam, Athens, Birmingham and Helsinki). The same measurements were conducted directly outside 152 homes spread over the metropolitan areas. Each home was monitored during 1 week. We assessed the temporal correlation and the variability of absolute concentrations. For all particle indices, including particle number, temporal correlation of 24-h average concentrations was high. The median correlation for PNC per city ranged between 0.67 and 0.76. For PM 2.5 median correlation ranged between 0.79 and

The electrochemical degradation of methylparathion has been investigated by using Ti/Pt as anode, Stainless Steel 304 as cathode, and sodium chloride as electrolyte. The pesticide is rapidly degraded, but full mineralization is not observed. Degradation products have been monitored through gas chromatography and mass spectrometry, and the overall degradation process has been monitored through dissolved and particulate organic carbon, sulfur, and phosphorus measurements. Several intermediates have been identified, and oxalic, formic, and acetic acids as well as tetraphosphorus trisulfide have been recognized as final products of the degradation process. A proposed mechanism of the process is presented.

BackgroundParticulate matter air pollution has been associated with adverse health effects. The fraction of ambient particles that are mainly responsible for the observed health effects is still a matter of controversy. Better characterization of the health relevant particle fraction will have major implications for air quality policy since it will determine which sources should be controlled.The RUPIOH study, an EU-funded multicentre study, was designed to examine the distribution of various ambient particle metrics in four European cities (Amsterdam, Athens, Birmingham, Helsinki) and assess their health effects in participants with asthma or COPD, based on a detailed exposure assessment. In this paper the association of central site measurements with respiratory symptoms and restriction of activities is examined.MethodsAt each centre a panel of participants with either asthma or COPD recorded respiratory symptoms and restriction of activities in a diary for six months. Exposure assessment included simultaneous measurements of coarse, fine and ultrafine particles at a central site. Data on gaseous pollutants were also collected. The associations of the 24-hour average concentrations of air pollution indices with the health outcomes were assessed in a hierarchical modelling approach. A city specific analysis controlling for potential confounders was followed by a meta-analysis to provide overall effect estimates.ResultsA 10 μg/m3 increase in previous day coarse particles concentrations was positively associated with most symptoms (an increase of 0.6 to 0.7% in average) and limitation in walking (OR= 1.076, 95% CI: 1.026-1.128). Same day, previous day and previous two days ozone concentrations were positively associated with cough (OR= 1.061, 95% CI: 1.013-1.111; OR= 1.049, 95% CI: 1.016-1.083 and OR= 1.059, 95% CI: 1.027-1.091, respectively). No consistent associations were observed between fine particle concentrations, nitrogen dioxide and respiratory health effects. As for particle number concentrations negative association (mostly non-significant at the nominal level) was observed with most symptoms whilst the positive association with limitation of activities did not reach the nominal level of significance.ConclusionsThe observed associations with coarse particles are in agreement with the findings of toxicological studies. Together they suggest it is prudent to regulate also coarse particles in addition to fine particles.