World War II was waged by officers who had been raised in the shadow of the first World War. Unsurprisingly, the gas attacks of the Great War trenches were still fresh in the collective mind of the U.S. military. This being the case, it was decided that in order to reduce casualties from weapons like mustard gas, soldiers needed a means of identifying airborne oxins before they could take effect. By now, Pauling was considered to be an expert in the detection of gaseous particles. In July 1942, having just finished his developmental work with the Pauling Oxygen Meter and still working with his carbon monoxide detector, Pauling was asked to begin research on an apparatus that could determine the size of particles present in smokes and gases. It was believed that by determining the size of particles in a contaminant, one could then identify the gas in question and respond accordingly.

Pauling began work on the apparatus right away. He believed that a stream of particles in a fog could be electrically charged and then, using data from an electrometer, drawn to points on a condenser plate. According to Stoke's Law, the rate at which these particles are attracted to the plate is inverse to the radius of the particle. By examining this grouping, Pauling argued that it would be possible to estimate the composition of the smoke being analyzed.

Encouraged by some early calculations, Pauling set a lab assistant, Charles Wagner, to the task of making preliminary measurements. His results were positive and Pauling chose to move the program forward. By 1943 he had a group of men making calculations, building the apparatus, and creating stable smokes for the testing process and by early 1944 the team was ready to put the device through its paces.

The initial tests were not good. The condenser plates were causing a bizarre phenomenon in which the largest particles were being grouped with the smallest, resulting in a highly inaccurate reading. And that was just the beginning of the team's problems. They quickly found that unfiltered air, such as that found in standard field conditions, contained a vast range of particles. In addition to the smoke or fog meant to undergo analysis, a typical sample could also contain dust, industrial pollutants, and natural contaminants like pollen. The distribution of precipitated particles was already making analysis difficult with clean samples; adding a host of impurities to the sample so complicated the results that an accurate determination was impossible for professional scientists. It was clear that a soldier in the field would be unable to operate the instrument effectively.

On March 28, 1944, Pauling filed his final report on the Particle Size Measurement Apparatus, number OEMsr-103. The project, he reported, was a failure. In his final write-up for the OSRD, Pauling suggested that the apparatus might be reworked to give a more accurate reading under controlled laboratory conditions. While he frankly admitted the instrument could "hardly be perfected for field use," he hoped that his work and that of his fellow researchers would not be in vain.