J William Nelson

Components of Lead in the Atmosphere of St. Louis, Missouri

Abstract By means of multiple linear regression analysis of a suite of more than 10 000 concentration measurements, of 14 elements at 11 sampling stations every 2 h over the course of a week in July 1975, Pb was found to be correlated in time most strongly with Br, secondarily with Zn, and also with K and Fe. At one station some Pb variation was apparently independent of other elements. On this basis and on the basis of wind directional relationships among the elements, at least four different components of Pb in the St. Louis aerosol may be identified.

Variation of Elemental Composition with Particle Size in the St. Louis Aerosol

Detailed particle size distribution of elemental constituents have been determined in the St. Louis aerosol by sampling with cascade impactors for particles >0.25 μm aerodynamic diameter and by analyzing using proton-induced X-ray emission, PIXE, for S, Cl, K, Ca, Ti, Mn, Fe, Zn, Br, and Pb. Two rooftop sites were selected for intensive sampling in industrial and residential locations in St. Louis during February 1974, every 12 h for a 7 d period which included clear, rainy, and snowy weather regimes. The data could be compared with the results of a similar study of the St. Louis aerosol during August 1973 when the weather was generally warm and without rain. Both data sets could also be compared with results of studies of Tallahassee, situated in coastal north Florida, and the north Atlantic marine atmosphere of Bermuda. Although variation in elemental concentrations and their size distributions were observed which could be associated with local weather conditions during the February sampling period, the data set was sufficiently large for meaningful average characteristics to be computed. As examples, two elements of pollution importance, sulfur and iron, show the following comparison between St. Louis and the Florida and Atlantic locations: Sulfur in all data sets was most abundant in the smallest particle size classes. Winter and summer concentration in St. Louis air were the same within a factor of two but generally exceeded north Florida concentrations. Bermuda concentrations were intermediate between St. Louis and north Florida, except for largest particles where sea spray derived material was present. The results reflect the importance of gas phase conversion to particulate forms of sulfur, e.g. sulfate, in all three locations. Iron concentrations in St. Louis generally exceeded those in north Florida for smallest particles and to a lesser extent for larger sizes. Concentrations in Bermuda were about 10-fold lower than in St. Louis for all particle sizes. The results reflect the terrestrial dust origin of iron and also suggest that iron is partially pollution-derived in the St. Louis atmosphere, especially in smaller size ranges. (Less)

Temporal variation in aerosol composition at summit, Greenland, summer 1989

At a high altitude site at Summit, Greenland, aerosol sulfur, chlorine, and potassium were found to occur mainly during sporadic high concentration episodes, lasting less than 24 h, over a much lowwer background level. Particle size resolved time sequence sampling was performed by automated two-stage streaker and high sensitivity elemental analysis by proton induced X-ray emission, PIXE, with a detection limit of 9 ng m−3. In a series of 165 4-h samples during one summer month in 1989, peak concentrations in the fine <2 μm diameter fraction were sometimes coincident and sometimes not, indicating different degrees of association of those elements in air masses passing over the site. Most of the S, Cl, and K was measured during the short high concentration episodes. This finding could not have been made by using a long time average sampling strategy.