In memoriam: Peter K. Mueller (1926–2023)

Remembering a long-time A&WMA member of more than 70 years

Peter K. Mueller passed away in early February at age 96. He was widely known for his expertise in air measurements and the design and oversight of major air pollution chemistry studies. Peter’s contributions derived from employment in state and federal government, and the private sector. He was a member of the Air & Waste Management Association for more than 70 years, received its 2007 Frank Chambers Excellence in Air Pollution Control Award, and was made an Honorary Member in 2015. His views and a sampling of achievements have been published earlier in A&WMA publications (Hidy et al. 2017; Hidy, Chow, and Watson 2017; Kleinman et al. 2017; Watson et al. 2017).

Peter’s involuntary transcontinental migration began with dislocation from Germany followed by a risky immigration to the United States. After enduring Kristallnacht when he was 11, Peter barely escaped the Holocaust, in which many members of his extended family were killed, when Peter and his father immigrated to England in May 1939, not long after his mother, brother, and sister immigrated to the United States. Later, Peter also moved to the United States, where he was drafted by the U.S. Army and served in the Medical Corps. Following this tour, he enrolled as a chemistry major at George Washington University, with subsequent graduate study at Rutgers University, where he focused on aqueous environmental chemistry. After receiving his Ph.D. degree, he moved to the San Francisco Bay Area as a chemist at the California State Air and Industrial Hygiene Laboratory (AIHL). His early experiences shaped his interest in chemistry and public health and led him to exacting standards as an expert in ambient air measurements. His research was aimed at informing policymakers about environmental conditions of concern.

Peter was the last of the first generation of environmental scientists who were challenged to characterize and understand photochemical smog. Arie Haagen Smit’s botanical experiments in Southern California led to the discovery of ozone formation from non-methane hydrocarbons and nitrogen oxides in ambient air (Haagen-Smit 1958). As AIHL director, Peter investigated instrumentation for quantitatively measuring smog products and precursors, recommended those that met quantitative reference standards, and characterized California’s unique air quality problems.

In the early 1950s, aerosol scientists recognized the significance of particle size in characterizing atmospheric aerosols. Obtaining size distributions was labor intensive and involved primitive means for sampling and analysis. By the 1960s, new size fractionating systems were being invented such as that of Goetz (1956). Peter and colleagues tested this sampler and improved its design (Mueller, Helwig, and Peterson 1959). As part of this project, they sampled urban air and found that, in contrast to earlier studies, airborne lead was concentrated in respirable particles, not just inhalable particles. This finding had important consequences for lung impacts and identification of gasoline fueled vehicles contributions to suspended particles. This result contributed to the formulation of automobile fuel composition rules later in the 1980s.

With mounting public and regulatory pressure to understand the nature of particles forming from gaseous emissions (secondary aerosols), Peter and the AIHL teamed with Kenneth Whitby, Sheldon Friedlander, Robert Charlson, and other investigators beginning in 1969 to conduct experiments on photochemical aerosols across California. The design and conduct of these studies employed unique, complex state of the art instrumentation for gas and particle measurements recorded by micro-computer. These projects (Hidy et al. 1975) advanced knowledge of aerosol gas interactions necessary to formulate effective emission reduction strategies.

In 1974, Peter joined Environmental Research and Technology (ERT) to partner with George Hidy in developing a western component of this company. Their goal was to use new concepts in environmental chemistry to inform policymakers of emerging issues. Peter oversaw improvements in ambient and laboratory analyses of air chemistry samples. Among the important achievements was the development of particle carbon analysis methods. These improved methods and their derivatives were applied in major urban studies such as Portland, OR, Los Angeles, Denver, CO, and Los Angeles, CA, to determine major aerosol components and to attribute ambient concentrations to sources. As co-investigators, Hidy and Mueller in cooperation with the Electric Power Research Institute (EPRI) initiated an extensive air monitoring network in the rural eastern United States that established effects of distant regional emissions on local particulate and ozone concentrations and acid deposition. Peter joined EPRI in 1982 to manage its air quality research program.

As the national air quality regulatory framework matured, EPRI’s research turned to public-private sector cooperative studies, well-suited for Peter’s collaborative skills. At EPRI, Peter initiated a wide range of studies, including plume and turbulence measurements, air toxics characterization, and visibility improvement. The North American Research Strategy for Tropospheric Ozone (NARSTO) involved government, academic, and industrial scientists across the United States, Canada, and Mexico in combined measurement and modeling studies to inform policymakers about emerging air quality issues. Starting around 1990, Peter led a cooperative project with the National Center for Atmospheric Research and a number of industrial and academic participants to improve the transparency and quality of climate modeling. This international project involved scientists from the United States, the United Kingdom, and Australia. The project urged modeling scientists to be more public about their work and the limitations of their 1980s model results.

With a lifetime of environmental research management, Peter retired from EPRI in the early 2000s and established a consulting entity to continue his environmental research interests. Peter leaves behind much more than his contributions to environmental science and the clean air over 330 million Americans breathe today: Peter embodied leadership and wisdom, gleaned from his professional and personal heritage, that he imparted to several generations of colleagues. Peter insisted on precision of written and spoken words: he taught us that clarity of words leads to clarity of thought. He insisted on measuring and communicating the accuracy and precision of numbers (“data”), starting with his own measurement responsibilities. He taught us to separate scientific “facts” from interpretation of these findings.

Peter will not only be known for his professional achievements, but also for his life with his wife Judy and his family, including his three daughters. Many ERT and EPRI alumni will remember him as a traveler with his top-down convertible and his pet dog beside him. Or later, seeing his devotion in retirement to the environmental cause by traveling with a Prius or on his bicycle. Unforgettable was Peter’s ride by Harley-Davidson motorcycle from Arizona to New Mexico for “story telling” with George Hidy and his wife.

Prepared by George Hidy, John Watson, Judith Chow, Sam Altshuler, Naresh Kumar,

and Pradeep Saxena.