Abstract
New particle formation (NPF), nucleation of condensable vapors to the solid or liquid phase, contributes significantly to atmospheric aerosol particle number concentrations. With sufficient growth, these nucleated particles may be a significant source of cloud condensation nuclei (CCN), thus altering cloud albedo, structure, and lifetimes, and insolation reaching the Earth’s surface. Herein we present one of the first numerical experiments conducted at sufficiently high resolution and fidelity to quantify the impact of NPF on cloud radiative properties. Consistent with observations in spring over the Midwestern USA, NPF occurs frequently and on regional scales. However, NPF is not associated with enhancement of regional cloud albedo. These simulations indicate that NPF reduces ambient sulfuric acid concentrations sufficiently to inhibit growth of preexisting particles to CCN sizes, reduces CCN-sized particle concentrations, and reduces cloud albedo. The reduction in cloud albedo on NPF days results in a domain average positive top of atmosphere cloud radiative forcing, and thus warming, of 10 W m−2 and up to ~50 W m−2 in individual grid cells relative to a simulation in which NPF is excluded.
Highlights
Atmospheric aerosol particles offset some fraction of the global warming associated with increased greenhouse gas concentrations.[1]
Prior to use of the WRF-Chem output to quantify the impact of New particle formation (NPF) on cloud properties, the simulations were subject to a detailed model performance evaluation
The root mean squared error (RMSE) is the same magnitude as inter-instrument uncertainty: The RMSE between the two instruments co-located at MMSF that operate with different particle size distributions (PSD) discretization and measurement principle (Scanning Mobility Particle Sizer (MMSF-scanning mobility particle sizers (SMPS)) and Fast Mobility Particle Sizer (MMSF-fast mobility particle sizers (FMPS))), calculated by treating one instrument as observation and the other as a predictor, is 7.8 × 103 cm−3
Summary
Atmospheric aerosol particles (hereafter aerosols) offset some fraction of the global warming associated with increased greenhouse gas concentrations.[1]. A number of challenges confront attempts to quantify the impact of NPF on CCN number concentrations and cloud properties at the local, regional, and global scale These include: (1) Uncertainties in the precise nucleation mechanism responsible for NPF and appropriate scaling parameters within NPF schemes. While previous numerical modeling and in situ measurement studies have suggested that a significant portion of global CCN originates from NPF,[13,14,15] the impact is regionally variable, scale dependent, and dependent on the assumed nucleation pathway.[16,17] (2) Uncertainties in, or challenges to, representation of the impact of NPF on gas phase concentrations, aerosol particle size distributions (PSD), and cloud droplet number concentrations (CDNC). Cray supercomputer), previous studies have either chosen to simulate relatively short periods (a few days or less),[36] simulate at comparatively low resolution requiring use of cumulus parameterizations,[38] employ a single prefactor,[31] or simplify the gas-
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