AAAR 41st Annual Conference

Plenary Sessions

Plenary I
Tuesday, October 3rd 8:00 AM – 9:15 AM
Friedlander Lecture: Particle-Resolved Modeling: A Bridge between Scales in Aerosol Science

Nicole Riemer

Session Abstract: Atmospheric aerosols are mixtures of different chemical species, and individual particles exist in many different shapes and morphologies. This “aerosol state” continuously evolves in the atmosphere. Thanks to advances in measurement techniques, we have made great progress in our process-level understanding of the atmospheric aerosol. Why is it then that aerosols and aerosol-cloud interactions are still associated with the largest uncertainties in global climate predictions? A key reason for this is the inherent multiscale nature of the problem—processes on the micro-scale determine macro-scale impacts—and the challenges that this poses for our modeling efforts. In this presentation I will show how high-detail particle-resolved modeling fills an important gap in the hierarchy of aerosol models. The particle-resolved approach represents the atmospheric aerosol using individual computational particles that evolve in size and composition as they undergo transformation processes in the atmosphere. While computationally expensive, this approach is therefore not limited by assumptions about particle composition within a given size range. As a result, it can represent the evolution of the full aerosol mixing state without simplifying assumptions. My presentation will illustrate how particle-resolved modeling can provide insights into the spatio-temporal evolution of aerosol mixing state, going beyond the traditional definitions of “externally” or “internally” mixed populations. I will show how simplifying the diversity of aerosol composition introduces errors in our estimates of climate-relevant properties, such as cloud condensation nuclei concentration and aerosol optical properties. I’ll conclude the presentation by summarizing the measurement challenges that we face in constraining particle-resolved models, but which provide a unique opportunity in “getting the right answer for the right reasons”.

Bio: Nicole Riemer is a Professor at the Department of Atmospheric Sciences and an Affiliate of the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign. She received her Doctorate degree in Meteorology from the University of Karlsruhe, Germany. Her research focus is the development of computer simulations that describe how aerosol particles are created, transported, and transformed in the atmosphere. Her group uses these simulations, together with observational data, to understand how aerosol particles impact human health, weather, and climate. Nicole Riemer received the NSF CAREER award, the College of Liberal Arts and Sciences Dean’s Award for Excellence in Undergraduate Teaching, and the AGU Ascent award. She is the co-chair of the Aerosol Processes Working Group of the Department of Energy Atmospheric System Research program, and editor for Aerosol Science & Technology and Journal of Geophysical Research.


Nicole Reimer


Plenary II
Wednesday, October 4th 8:00 AM – 9:15 AM
AEESP Lecture: Anti-racist air-quality modeling

Julian Marshall

Session Abstract: Ambient air quality in the US has improved over time, thanks to steps such as the 1970 Clean Air Act. However, in part because of where pollution sources are located, people of color in the US are still, on average, more exposed to air pollution than are white Americans. Today, society’s goals for air quality include not only improving conditions overall, but also addressing systemic disparities. Models and measurements are needed to focus attention on how to achieve that goal; research is needed to help propose and test possible solutions.

This talk will discuss existing exposure-disparities and the need to evaluate strategies to eliminate them. Three aspects will be emphasized:

(1) We don’t all breathe the same air.
Today, the largest exposure disparities are by race-ethnicity. Disparities by race are larger than, and statistically distinct from, those by income. Exposure disparities reflect segregation of people and of pollution, which in turn reflect norms, laws, enforcement, acts of violence, and threats of violence, which have reenforced segregation. Over time, polluting land uses were more likely to locate in communities that lacked political power to object.

(2) The past is present.
Contemporary disparities reflect recent actions but also actions many decades ago. Race-based planning implicitly and explicitly included race in deciding where to locate polluting land-uses.

(3) The disparities won’t eliminate themselves.
Improvements since 1970 reflect substantial attention and resources. Similar attention and resources will be needed to address exposure disparities. If future emission-reductions follow historic patterns, then future improvements to exposures will continue to reduce average exposures (a good outcome) but maintain relative disparities. Eliminating disparities requires spatially targeted emission-reductions that clean the air especially for overburdened communities.

In light of these facts, aerosol researchers can play a valuable role by using data and models to investigate how to eliminate existing exposure disparities.

Bio: Julian Marshall is a Professor in the Department of Civil and Environmental Engineering at University of Washington. He also is Director of the Grand Challenges Impact Lab, and an adjunct professor in Global Health. Dr. Marshall’s research focuses on measurements and models to understand human exposure to air pollution, especially understanding and addressing inequities in exposure.

Dr. Marshall has published more than 170 peer-reviewed journal articles; his publications include several “most-read” / “most-downloaded” articles and multiple articles in top journals such as Science and Proceedings of the National Academy of Sciences. Grants he has contributed to during his career total >$40m.

Dr. Marshall teaches classes in Air Quality Engineering, and in Justice, Equity, Diversity, and Inclusion for Civil and Environmental Engineers. He also teaches the Grand Challenges Impact Lab (GCIL) course, a 10-week UW study abroad class in Bangalore, India; GCIL students work with local organizations and use social entrepreneurship and engineering problem-solving to address social, health, and environmental challenges in India.

His awards include the Joan M. Daisey Outstanding Young Scientist Award from the International Society of Exposure Science, a McKnight Professorship from University of Minnesota, the Young Engineer of the Year award from the Minnesota chapter of the American Society of Civil Engineers, and the Kiely Professorship at University of Washington.

Dr. Marshall earned a BSE in Chemical Engineering (High Honors) from Princeton, and a MS and PhD in Energy and Resources from UC Berkeley.

Julian Marshall


Plenary III
Thursday, October 5th 8:00 AM – 9:15 AM
Lundgren-Marple Lecture: Synergies Between Aerosol Measurements from Satellites and in-situ at the Nose Level

Vanderlei Martins

Session Abstract: The detailed measurement of aerosol microphysical properties from space provides unique capability for monitoring global aerosols on a daily basis. Multiple techniques are available spanning from LIDAR profiles to multi-angle, multispectral, and hyperspectral radiances measured in different polarization states. This wide variety of parameters provide multiple independent variables that can be inverted for the detailed inference of aerosol amount (optical thickness), particle size distributions, particle shape parameters, real and imaginary refractive indices, single scattering albedo, etc.

The same multi-angle and polarization techniques used on satellite measurements can also be used for in-situ measurements with a polarized polar nephelometer. The added synergy and advantages in having total column and surface measurements performed simultaneously, with the same technique, will be explored in this talk. In-situ measurements also bring the added advantage of allowing for aerodynamic separation, and for detailed chemical measurements, both of which we want to interpret together with the satellite total column measurements.

In this talk we will show the application of the Generalized Retrieval of Aerosol and Surface Properties (GRASP) inversion algorithm to retrieve aerosol microphysical properties from remote sensing as well as from in situ aerosol measurements. Specific results include laboratory measurements with different aerosol types, results from past field campaigns, remote sensing results from the HARP CubeSat and from the ADLER-2/GAPMAP satellites, as well as future measurements with the HARP2 sensor on the NASA PACE observatory. In particular, we will show results from two years of HARP CubeSat data collected around the globe, and results from the current GAPMAP sensor, which is still on Earth’s orbit, including aerosol retrievals over dust and biomass burning smoke. In situ results will be discussed from multiple versions of integrating nephelometers, from the Polarized Imaging Nephelometer, and from the newly developed IMAP instrument, all measuring the optical and microphysical properties of aerosols.

Bio: Dr. Martins is a Professor in the Department of Physics of the University of Maryland Baltimore County, Director of UMBC’s Earth and Space Institute, and a member of the Goddard Earth Sciences Technology and Research center (GESTAR) II between UMBC and NASA Goddard, leading the Laboratory for Aerosols, Clouds and Optics (LACO). He is the PI for the HARP2 instrument set to fly in the NASA PACE observatory to collect global aerosol and cloud data, the PI for the HARP CubeSat satellite, and the PI for the AirHARP airborne instrument. He was a member of the Glory and the MODIS science teams, and of the ACE decadal survey Science Working group helping to define the requirements for the next generation of cloud and aerosol measurements from space. For the last 15 years, Dr. Martins has worked closely with Engineers and Scientists from NASA GSFC to develop new instrumentation for the measurement of aerosol and cloud microphysical parameters in the laboratory, from aircraft, and from satellites. He developed the concept and airborne instrumentation for cloud side measurements (the cloud scanner spectrometer), the polarized imaging nephelometer systems (PI-Neph and OI-Neph), the rainbow camera, the PACS imaging polarimeter, and the HARP polarimeter family. He also participated in the development and patent of a portable X-Ray instrument for laboratory, field, and space applications. He is currently training and advising several instrument scientist students on the development of instrumentation to measure detailed properties of aerosol and cloud particles. Dr. Martins is also the Chief Technology Officer (CTO) for the GRASP/AirPhoton company leading their technological developments including the implementation of the in-situ IMAP polar nephelometer, and the constellation of GAPMAP satellites for the measurement of aerosol microphysics from space.

Vanderlei Martins


Plenary IV
Friday, October 6th 11:00 AM – 12:15 PM
The role of aerosol science in understanding and minimizing the risk of airborne infection transmission

Lidia Morawska

Session Abstract: The term “prevention of infection transmission” evokes in most people an image of a white-clad medical professional, shielded from head to toe in personal protective equipment, while disinfecting, testing, or performing medical procedures on infectious patients. But apart from physicists and other scientists working in this field, few people realise that in fact physics, and more specifically aerosol physics, plays a major role in infection transmission. The interdisciplinary nature of the process of infection transmission makes it an immensely complex and interesting area to study, but also opens the door to misunderstanding and misinterpretation.

Understanding the numerous physical mechanisms involved in infection transmission is critically important in lowering the risk of infection transmission; this is where aerosol science comes to the fore. Yet the broader role of aerosol science is to interact and communicate with other scientific fields, particularly the medical community, to facilitate an understanding of the physics of the process in the “languages” of these disciplines. When the physics is understood, appropriate risk mitigation measures can be implemented according to the roles and responsibilities of these disciplines.

The problems start with the definitions of aerosol science terms. Aaccording to aerosol science, an aerosol is defined as “an assembly of liquid or solid particles suspended in a gaseous medium long enough to enable observation or measurement” (Kulkarni et al. 2011). In contrast, medical science defines an aerosol as a small particle, while a droplet is a particle larger than 5 µm. Discussion about the terminology is still raging and dividing expert communities, so to help unite the fields, we propose to use the term particles, rather than aerosols or droplets, [Morawska and Buonanno, 2021].

But addressing the terminology is just the beginning. The next step is to develop a quantitative understanding of particle generation, particle emission, particle evaporation, particle flow dynamics, and particle disposition.

Particle generation occurs in the respiratory tract during human respiratory activities, which include breathing, speaking, singing, or coughing. After the particles are emitted, complex physico-chemical reactions occur as a result of particle evaporation in the air and flow dynamics drive the process of particle transport between the infected and a susceptible person. The final step is the disposition of the particles in the respiratory tract of the susceptible person, at which point the biological process of infection starts.

How well do we understand these processes? In our recent review on this topic [Morawska and Buonanno, 2021], we concluded that although the generation of particles in the respiratory tract is understood qualitatively, there is little quantitative knowledge about the characteristics of particles emitted during respiratory activities, their fate after emission, and their deposition during inhalation. More studies are clearly needed to address these knowledge gaps.

However, we should not discount the importance of what we actually do know, and how we can and should use this knowledge in lowering the risk of infection. I previously advocated for the use of our knowledge base to prevent infection after the SARS1 epidemic (Morawska, 2006). Since then, many studies using novel technologies have increased our understanding of the size distribution of particles from our respiratory processes and demonstrated that particles emitted from our respiratory activities can be suspended in the air for a long time and travel long distances in the indoor environment. A fraction of the virus contained by the particles remains infectious during this process (Oswin et al., 2022).

The hard lessons of the COVID pandemic have led to the realisation that as a society we have not effectively used the knowledge we already have. One of the key directions to follow to improve our future performance is to develop and legislate indoor air quality standards that include control of infectious respiratory particles emitted by building occupants. Our paramount argument continues to be that clean indoor air is a basic human right (Morawska, 2022).

Bio: Lidia Morawska is Distinguished Professor at the Queensland University of Technology in Brisbane, Australia, and the Director of the International Laboratory for Air Quality and Health at QUT, which is a Collaborating Centre of the WHO. Lidia also holds positions of Vice-Chancellor Fellow, Global Centre for Clean Air Research (GCARE), University of Surrey, UK and of Adjunct Professor, Institute for Environmental and Climate Research (ECI), Jinan University, Guangzhou, China. She conducts fundamental and applied research in the interdisciplinary field of air quality and its impact on human health and the environment, with a specific focus on science of airborne particulate matter. She is a physicist and received her doctorate at the Jagiellonian University, Krakow, Poland for research on radon and its progeny. An author of close to one thousand journal papers, book chapters and refereed conference papers, Lidia has been involved at the executive level with several relevant national and international professional bodies, is a fellow of the Australian Academy of Science and a recipient of numerous scientific awards, including L’Oréal-UNESCO Award 2023 for Women in Science. She was named one of TIME100 world’s most influential people for 2021, for her global leadership work on the importance of airborne transmission of SARS-CoV-2.

Lidia Morawska

Dates to Remember

October 2 - 6, 2023
AAAR 41st Annual Conference

Code of Conduct


Oregon Convention Center
777 NE Martin Luther King Jr. Blvd.

Portland, OR 97232


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Retiree $275 $275 $366