Probing the vertical profile of new particle formation and growth with models and observations
Smith, James — University of California, Irvine
Pierce, Jeffrey Robert — Colorado State University
Area of research
This study seeks insights into the governing mechanisms of new particle formation (NPF) over the central United States and the possible role that vertical mixing may play in boundary-layer NPF. Understanding what drives the vertical profile of NPF (e.g., gradients of temperature and gas-phase precursors), and how the vertical profile corresponds to what is observed at the surface, is essential to both interpreting observations and correctly modeling NPF in the atmosphere.
The findings show that the vertical profile of temperature, NPF precursors, and vertical mixing play a dominant role in shaping the vertical profile of NPF in the central United States. In our work, we found the highest NPF rates occurring near the interface of the mixed layer and the residual layer. This layer of the atmosphere is also relevant to cloud formation: Thus, newly formed particles can potentially impact cloud formation and properties.
We used data from the Holistic Interactions of Shallow Clouds, Aerosols, and Land Ecosystems (HI-SCALE) campaign, which took place at the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) user facility's Southern Great Plains (SGP) observatory in North-central Oklahoma in 2016. We chose four NPF events and two non-events to analyze, and aerosol data collected aboard the ARM Aerial Facility (AAF) Gulfstream-159 (G-1) aircraft show elevated concentrations of nucleation-mode particles at often shallow levels close to the developing mixed layer or in the residual layer. We used data collected at the SGP observatory and by the G-1 aircraft to inform and constrain our modeling of the vertical column. We used a one-dimensional chemistry and aerosol microphysics model to investigate the drivers of the NPF over the SGP observatory. The model was largely able to reproduce the observations of four NPF events and two non-events at the surface, and the model showed that the highest NPF rates usually occurred just below the top of the developing mixed layer. Figure 1 gives an overview of our analysis of NPF and growth, including the connection between NPF aloft and ground-level observations. We performed a sensitivity analysis to understand the drivers of the vertical profile, and we found the most potent governors of NPF are the vertical profile of temperature, gas-phase species, and vertical mixing.