Effect of dust particle size on atmospheric radiative forcing

Dust significantly influences the environment, climate, air quality, and solar energy systems in arid regions such as the Middle East. These impacts are strongly size-dependent. Observations of dust deposition (DD) indicate that coarse particles (geometric radius r > 10 μm) dominate the deposited mass, yet are largely excluded from current aerosol models, which are primarily constrained by satellite-derived aerosol optical depth (AOD). This omission leads to substantial underestimation, by up to a factor of three, of both dust emission (DE) and DD in models and reanalysis products.

This study is the first to jointly constrain dust simulations using both AOD and DD observations to quantify the roles of fine and coarse particles, employing the WRF-Chem model. We find that coarse dust accounts for over 70% of total DE but contributes less than 10% to surface shortwave (SW) radiative forcing (RF). The annual mean net RF due to dust over the Arabian Peninsula and surrounding seas can locally reach −25 W m², with even stronger forcing—up to −60 W m² — observed in some regions, such as the southern Red Sea. Fine particles (r < 3 μm) dominate airborne dust, causing substantial solar dimming (5–10%), surface cooling, and reduced photovoltaic efficiency. In contrast, coarse particles drive DD processes, reducing solar panel performance by 2–5% per day.

These findings underscore the importance of explicitly representing coarse dust in atmospheric models and data assimilation systems. Improved treatment of particle size distributions is essential for accurate dust mass budgets and reliable assessments of dust impacts on regional climate and solar energy infrastructure.