Atmospheric particulate absorption and black carbon measurement.

It is convenient to measure the optical attenuation A of the combination of a layer of atmospheric particulate matter and the quartz fiber filter on which it has been collected. The problem of relating A to the absorption and scattering coefficients k and s of the particulate matter itself is treated as a problem in diffuse reflectance spectroscopy using the KubelkaMunk theory. The results show that although, in general, A is a nonlinear function strongly dependent on both s and k, for a limited range of s and sample thickness d, A can be a practically linear function of k. Fortunately, this range includes that common to atmospheric particulate samples. Furthermore, it is shown that if the filter's reflectance is sufficiently high, A can be nearly independent of s. This is in agreement with experimental and, for the limiting case when the substrate filter reflectance is unity, theoretical results obtained by other researchers. Use of such measurements of A as a means of determining the black carbon mass loading C on a filter is also investigated. It is shown that when the black carbon mass fraction f(c) is high, as it is for samples collected in large urban areas, A is a predictable and practically linear function of C. However, when f(c) is low, as it is for many rural locations, then the slope of the function A(C) is strongly dependent on f(c), leading to possible overestimates of C. This problem can be alleviated by making the measurement of A at near-infrared wavelengths rather than in the visible spectrum.

Absorption-coefficient-determination method for particulate materials.

A method is presented for determining the optical absorption coefficient, or the imaginary refractive index, of particulate material that has been collected from aerosols or hydrosols by means of filtration. The method, based on the Kubelka-Munk theory of diffuse reflectance, is nondestructive and requires no other knowledge of the sample than the amount present, the specific gravity, and an estimate of the real index of refraction. The theoretical development of the method is discussed along with an analysis of photometric and gravimetric errors. We test the method by comparing results obtained for powdered didymium glass with measurements made before the glass was crushed. An example of the method's application to the determination of the absorption coefficient of atmospheric dust at UV, visible, and near-IR wavelengths is also presented.

Imaginary refractive index of buckyballs.

The UV, visible, and IR imaginary refractive indexes of C(60) are determined and compared with that of carbon soot.

Carbon and the optical properties of atmospheric dust.

Atmospheric particulate matter was examined to estimate the significance of free carbon as an absorber of near-ultraviolet, visible, and near-infrared radiation. Bulk and size-fractionated samples have been disassembled into acetone-soluble, water-soluble, and insoluble fractions. The absorption coefficients for these fractions, and for the insoluble material after removal of the free carbon by burning, have been measured. The results show that in the visible and near infrared, free carbon, although not a major component by mass, is by far the dominant absorbing material. These measurements in relation to otherresearch suggest that geographic variations in and anthropogenic contributions to the free-carbon content cause much of the variation in the absorption coefficient of atmospheric particulate samples.

Pneumothorax in drug abusers. An urban epidemic?

Although intravenous drug abuse is endemic in urban America, only 19 cases of pneumothorax from neck injections have been reported. For this reason, the experience at Detroit Receiving Hospital was reviewed. Data collected included patient demographics, size of pneumothorax, use of antibiotics, and complications related to tube thoracostomy. Of 525 diagnoses of pneumothorax between January 1, 1982 and December 31, 1984, 113 (21.5%) occurred as a result of drug abuse in 84 patients. Average patient age was 32 years (range 20 to 55 years). Thirty-eight (45%) were female. The number of admissions per year has increased, and 11 patients showed multiple admissions over the 3-year study period. Nine patients had bilateral collapse. One hundred six pneumothoraces (94%) were treated with closed thoracostomy with a tube-related hospital stay of 5 days, overall stay averaging 7 days. Only six patients received antibiotics for chest tube prophylaxis, and no in-hospital tube-related infections were identified. Thirteen patients developed residual pneumothorax following tube removal, but only two required a new tube. Pneumothorax in drug abusers is a serious urban problem and one with which physicians need be familiar.