Lead halide aerosols. Properties of environmental significance

Abstract

one type apparently arises when the air in the city becomes stagnant, while another type is clearly associated with unusually large industrial emissions. The Pb/Br ratio is not a practical tool for measuring the relative amounts of pollution from industrial and automotive sources-at least in an area with no strong industrial sources of Pb. AcknowledgmentThe authors would like to acknowledge the assistance of D. Yesso in preparing standard solutions, and of W. Strang of the Allegheny County Air Pollution Bureau who provided data on carbon monoxide and fine particulates in the Pittsburgh area.

Atmospheric chemistry of automotive lead

“…In most cases, PbBrCl was the only crystalline phase identified with all the interplanar d spacings being assigned, while in a few cases PbO was also detected at a very trace level. The finding of only PbBrCl, which had a consistent Br/Cl ratio of 1.0 as indicated by the diffraction pattern (14), must reflect the engine sampling conditions. The fuel used was commercial Texaco 3-star with a mole ratio of Pb:EDB:EDC of 1:0.5:1.…”

“…The latter workers suggested that the halogen loss from the lead halide compounds emitted from the exhaust was due to simple acid-base reactions involving carbonate or hydroxide ions, rather than a photolytic process, but did not explain the source of these ions in the atmosphere. This mechanism was further investigated by Boyer and Laitinen (14), who examined the reaction of laboratory-pure lead halide aerosols with CO2 and H2O vapor and found that the lead halide was quite stable with respect to reaction with these species, both in the presence and absence of light of wavelength 300-400 nm. They exposed PbBrCl to 9% CO2 in moist air at 50 °C in the dark over a 72-h period and found only 0.4% halide loss during decomposition, with slight enhancement during illumination, concluding that the large halogen losses observed from automobile exhaust particulates could not be replicated in the absence of the automotive exhaust environment.…”

“…A qualitative elemental analysis has been performed using a scanning electron microscope coupled to an X-ray energy dispersive spectrometer (SEM/XES), upon individual particles collected from the atmosphere (15)(16)(17). Ter Haar and Bayard (13), using an electron microprobe (EMP), reported the identification of 14 different lead compounds in atmospheric samples. However, the limitations of the EMP technique used by these workers have since been pointed out by Heidel and Desborough (18) and considerable doubt must attach to the structural assignments.…”

Influence of tetraethyllead and lead scavengers on oxidation of carbon monoxide and hydrocarbons over platinum and palladium

“…It is known that many different lead compounds can be formed by the interaction of TEL, EDB, and EDC (5), of which lead bromochloride is the most abundant (6). The reaction products are strongly dependent on temperature and oxygen/fuel ratio.…”

Lead Contamination of the Roadside Ecosystem

“…Several other studies provide evidence to suggest that halogens may not be lost from exhausted lead salts. 25 Boyer and Laitinen 25 evaluated the stability of laboratory pure lead halide aerosols toward halogen loss by hydrolytic exchange with H 2 O, CO 2 , and ultraviolet light and concluded that halogens were not lost under their laboratory (non-automotive exhaust environment) conditions. Bomback et al 26 have observed that the lead salts PbSO 4 and Pb 3 (PO 4 ) 2 accumulate in catalytic converters and that deposits containing these salts may periodically break off and be exhausted.…”