Smog Detector

The Charlson Nephelometer and Climate Research

Integrating Nephelometer attached to aircraft (flickr.com)

By 1965, smog plagued cities across the United States. Los Angeles notoriously had some of the dirtiest air in the world. In addition to poor visibility, smog also caused respiratory health issues.

Smog is essentially a high concentration of sulfate aerosols in the atmosphere. Sulfates are produced in the combustion of fossil fuels in factories, plants, refineries, and – the primary culprit in Los Angeles – automobiles. The sulfates produced by combustion become aerosols – fine particles suspended in air.

Scientists did not understand the effects of sulfate aerosols in the atmosphere until Dr. Robert Charlson invented the first device to quantify sulfate aerosols in the atmosphere in 1965. The nephelometer has since facilitated local and global understandings of air quality and climate.

Smog over Los Angeles, 1948 (kcet.org)

Robert Charlson looks on with nephelometer prototype in hand as Vice Provost for Research Donald Bevan receives royalty from the patent. (washington.edu)

Prior to the nephelometer, scientists estimated aerosol concentrations in the atmosphere with the eye test. At first, the device was used to analyze how light was scattered by aerosols. Once Charlson and his team understood how aerosols scattered light, the device could be used to measure the number of aerosols in a given part of Earth’s atmosphere. These measurements provide an understanding of a region’s air quality and visibility.

Carlson’s nephelometer produced the first royalty-bearing patent held by the University of Washington. The device has improved over the years and is now marketed by TSI Incorporated as the Model 3563 Integrating Nephelometer. The device is commonly used for measurements related to climate, visibility, and air quality.

Nephelometer Patent and Design

Patent for Integrating Nephelometer

TSI Integrating Nephelometer Design

Map of aerosol cooling effect (noaanews.noaa.gov)

While Charlson published papers on the role of aerosols in affecting the global heat balance in 1969 and 1976, the significance of these findings went largely unnoticed until debates over global warming became more prevalent around 1990. Made possible by his invention of the nephelometer, Charlson’s research has produced an understanding of the aerosol cooling effect. While greenhouse gases generally have a warming effect, the aerosol cooling effect is concentrated over industrial areas in the Northern Hemisphere. The regionally specific concentrations of sulfate aerosols mean that regional changes in weather patterns supplement an overall increase in average global temperature as human-produced climate change continues.