About
Nicole Riemer is a professor whose research focuses on atmospheric sciences, particularly particle-resolved modeling of aerosols and their interactions in the atmosphere. Her work involves understanding the chemical and physical processes of aerosols, including black carbon, organic-inorganic internally mixed particles, and their effects on water uptake, optical properties, and climate. She has contributed to advancing the modeling of aerosol mixing states, in-cloud aqueous phase chemistry, and the impacts of aerosols on climate and air quality. Her background includes extensive collaboration with graduate students and postdoctoral scholars, and her research has been published in various atmospheric science contexts. She actively seeks new graduate students for her group and can be contacted for questions about projects and applications within her department.
Research topics
- Meteorology
- Environmental science
- Chemistry
- Geology
- Atmospheric sciences
- Optics
- Geography
- Environmental chemistry
- Physics
- Computational physics
- Climatology
- Materials science
Selected publications
Quantifying the effects of mixing state on aerosol optical properties
Atmospheric chemistry and physics · 2022 · 38 citations
Senior authorCorresponding- Atmospheric sciences
- Chemistry
- Computational physics
Abstract. Calculations of the aerosol direct effect on climate rely on simulated aerosol fields. The model representation of aerosol mixing state potentially introduces large uncertainties into these calculations, since the simulated aerosol optical properties are sensitive to mixing state. In this study, we systematically quantified the impact of aerosol mixing state on aerosol optical properties using an ensemble of 1800 aerosol populations from particle-resolved simulations as a basis for Mie calculations for optical properties. Assuming the aerosol to be internally mixed within prescribed size bins caused overestimations of aerosol absorptivity and underestimations of aerosol scattering. Together, these led to errors in the populations' single scattering albedo of up to −22.3 % with a median of −0.9 %. The mixing state metric χ proved useful in relating errors in the volume absorption coefficient, the volume scattering coefficient and the single scattering albedo to the degree of internally mixing of the aerosol, with larger errors being associated with more external mixtures. At the same time, a range of errors existed for any given value of χ. We attributed this range to the extent to which the internal mixture assumption distorted the particles' black carbon content and the refractive index of the particle coatings. Both can vary for populations with the same value of χ. These results are further evidence of the important yet complicated role of mixing state in calculating aerosol optical properties.
Aerosol–Ice Formation Closure: A Southern Great Plains Field Campaign
Bulletin of the American Meteorological Society · 2021 · 77 citations
- Environmental science
- Atmospheric sciences
- Meteorology
Abstract Prediction of ice formation in clouds presents one of the grand challenges in the atmospheric sciences. Immersion freezing initiated by ice-nucleating particles (INPs) is the dominant pathway of primary ice crystal formation in mixed-phase clouds, where supercooled water droplets and ice crystals coexist, with important implications for the hydrological cycle and climate. However, derivation of INP number concentrations from an ambient aerosol population in cloud-resolving and climate models remains highly uncertain. We conducted an aerosol–ice formation closure pilot study using a field-observational approach to evaluate the predictive capability of immersion freezing INPs. The closure study relies on collocated measurements of the ambient size-resolved and single-particle composition and INP number concentrations. The acquired particle data serve as input in several immersion freezing parameterizations, which are employed in cloud-resolving and climate models, for prediction of INP number concentrations. We discuss in detail one closure case study in which a front passed through the measurement site, resulting in a change of ambient particle and INP populations. We achieved closure in some circumstances within uncertainties, but we emphasize the need for freezing parameterization of potentially missing INP types and evaluation of the choice of parameterization to be employed. Overall, this closure pilot study aims to assess the level of parameter details and measurement strategies needed to achieve aerosol–ice formation closure. The closure approach is designed to accurately guide immersion freezing schemes in models, and ultimately identify the leading causes for climate model bias in INP predictions.
The acidity of atmospheric particles and clouds
Atmospheric chemistry and physics · 2020 · 741 citations
- Chemistry
- Environmental chemistry
- Environmental science
, HCl, and organic acids and bases as well as chemical reaction rates. It has implications for the atmospheric lifetime of pollutants, deposition, and human health. Despite its fundamental role in atmospheric processes, only recently has this field seen a growth in the number of studies on particle acidity. Even with this growth, many fine particle pH estimates must be based on thermodynamic model calculations since no operational techniques exist for direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally-constrained pH estimates are limited in spatial and temporal coverage. Clouds and fogs are also generally acidic, but to a lesser degree than particles, and have a range of pH that is quite sensitive to anthropogenic emissions of sulfur and nitrogen oxides, as well as ambient ammonia. Historical measurements indicate that cloud and fog droplet pH has changed in recent decades in response to controls on anthropogenic emissions, while the limited trend data for aerosol particles indicates acidity may be relatively constant due to the semi-volatile nature of the key acids and bases and buffering in particles. This paper reviews and synthesizes the current state of knowledge on the acidity of atmospheric condensed phases, specifically particles and cloud droplets. It includes recommendations for estimating acidity and pH, standard nomenclature, a synthesis of current pH estimates based on observations, and new model calculations on the local and global scale.
Recent grants
Multiphase Atmospheric Chemistry Impacts with PartMC and MultiChem
NSF · $653k · 2019–2024
CAREER: Particle-Resolved Models for Aerosol-Cloud Interactions
NSF · $597k · 2013–2019
A Particle-Resolved Aerosol Model of Soot Aging
NSF · $492k · 2008–2012
Frequent coauthors
- 65 shared
Matthew West
University of Illinois Urbana-Champaign
- 28 shared
Jeffrey H. Curtis
University of Illinois Urbana-Champaign
- 25 shared
Joseph Ching
- 24 shared
Zhonghua Zheng
Jilin Medical University
- 19 shared
H. Vogel
- 18 shared
J. Tian
University of Illinois Urbana-Champaign
- 16 shared
Matthew L. Dawson
- 16 shared
R. A. Zaveri
Pacific Northwest National Laboratory
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