Dear Colleagues, If your research uses analytical techniques used for the study of nano-components of anything in the realm of geochemistry, including but not limited to geochemical cycles, weathering, climate impacts, aqueous geochemistry, environmental science, human health science, geophysics, ore deposits, mineralogy and petrology, isotope geochemistry, and any other Earth related field the involves the smallest scales, please consider submitting an abstract to this session. Session organizers: James Ranville (jranvill@mines.edu<mailto:jranvill@mines.edu>) and Aaron Goodman (agoodman@mines.edu<mailto:agoodman@mines.edu>) of the Colorado School of Mines, Golden, Colorado, USA. Keynote speaker: Michael Hochella, University Distinguished Professor, Virginia Tech. Full session description: Elemental geochemical cycles are significantly influenced by nano- and sub-micron scale particles. Geogenic nanoscale materials play important roles in a variety of systems including but not limited to atmospheric chemistry, nutrient cycling, water chemistry, sediment budgets, dispersion of economically-valuable minerals, and soil chemistry. While geogenic nanoparticles (NPs) dominate global fluxes, the emergence of engineered and incidental NPs is increasingly concerning in localized (e.g. urban) environmental systems. Due to their small size and higher fraction of surface atoms, both natural and anthropogenic NPs have increased reactivity compared to larger particles, often resulting in unique elemental behavior and potential for negative effects on biota. Measuring NPs in environmental samples is challenging, and obtaining accurate measurements is critical to understanding their full impact on geochemical cycles. Particle number/concentration, mass/size distributions, and elemental/mineralogical composition are all vital to characterizing NP populations. Recent advances in analytical techniques have made all of these measurements possible, however knowledge gaps remain as to their accuracy. Techniques including field flow fractionation (FFF) and single particle ICP-MS can characterize NPs in aqueous suspension, while aerosol particle sizers can evaluate airborne NP populations in situ, and microscopies such as TEM can measure NPs in solid matrices. Closing knowledge gaps in the science of measuring nanoparticles will directly influence the ability to understand their geochemical significance. As such, this session invites contributions that advance the measurement of nanoparticles in environmental systems, and/or contribute to our understanding of nanogeochemical cycles.