Dr. Beverly Cohen and her colleagues at New York University School of Medicine tested the performance of iron nanofilms to collect and measure sulfuric acid particles of different sizes under a variety of temperature and humidity conditions. The iron nanofilm detector is a thin iron-coated silicon chip. Particles would react with the iron, creating an elevated site or bump on the film surface, which can be visualized using an atomic force microscope. Based on previous research by the investigators, elevated sites surrounded by a ring were assumed to reflect acidic particles; sites without rings were assumed to represent nonacidic particles. The authors tested the performance of iron nanofilms preexposed to laboratory-generated sulfuric acid particles of different sizes under a variety of storage conditions. They also conducted a field study, using two types of air samplers for ambient monitoring, an electrostatic aerosol sampler (which was preceded by a microorifice impactor that removed particles larger than 100 nm), and an ultrafine diffusion monitor, which did not have specific size selectivity.