PHYSICAL AND CHEMICAL CHARACTERIZATION OF ATMOSPHERIC ULTRAFINE PARTICLES IN THE LOS-ANGELES AREA

Atmospheric ultrafine particles (diameter < 0.1 mu m) are under study by inhalation toxicologists to determine whether they pose a threat to public health, yet, little is known about the chemical composition of ultrafine particles in the atmosphere of cities. In the present work, the number concentration, size distribution, and chemical composition of atmospheric ultrafine particles is determined under wintertime con ditions in Pasadena, CA, near Los Angeles. These experiments are condu cted using a scanning differential mobility analyzer, laser optical co unter, and two micro-orifice impactors. Samples are analyzed to create a material balance on the chemical composition of the ultrafine parti cles. The number concentration of ultrafine particles in the size rang e 0.017 < d(p) < 0.1 mu m, analyzed over 24-h periods, is found to be consistently in the range 1.3 x 10(4) +/- 8.9 x 10(3) particles cm(-3) air. Ultrafine particle mass concentrations are in the range 0.80-1.5 8 mu g m(-3). Organic compounds are the largest contributors to the ul trafine particle mass concentration. A small amount of sulfate is pres ent in these particles, at concentrations too low to tell whether it e xists as unneutralized sulfuric acid. Iron is the most prominent trans ition metal found in the ultrafine particles. These data may assist th e health effects research community in constructing realistic animal o r human exposure studies involving ultrafine particles.