Anthropogenic aerosols prolong fog lifetime
Liu, Yangang — Brookhaven National Laboratory
Area of research
Aerosol-cloud interactions, especially aerosol effects on cloud lifetime, remain uncertain and pose great challenges to the scientific community. Challenges stem from the lack of long-term measurements and covariation of aerosol and meteorological variables that can mask aerosol effects. This study addresses these problems by analyzing decades-long measurements in China of fog lifetime, aerosol loading, and meteorological variables and conducting numerical modeling.
We find that an increase in aerosol loading prolongs fog lifetime by primarily delaying fog dissipation. The finding has important implications for understanding aerosol effects on fog life cycle, which also provides insights into aerosol effects on boundary-layer clouds that share similar warm-cloud microphysical processes but lack such long-term measurements of life cycle.
We investigate aerosol-fog interactions, analyzing 52 y (1960-2011) of measurements in China coupled with modeling studies. The measurements were collected at 404 meteorological stations that included fog start and end times, aerosol loading (proxied by clear-sky visibility), and meteorological variables (e.g., temperature and relative humidity). We find that fog lifetime exhibits a clear increasing trend over time and that this increase is mainly attributable to a delay in fog dissipation. Increased aerosol levels and global warming are found to affect fog lifetime in opposing ways: increased aerosol levels serve to prolong fog lifetime by primarily delaying fog dissipation, whereas warming shortens fog lifetime by primarily delaying fog formation. Overall, the aerosol effect on fog lifetime in China is found to dominate, especially in the highly polluted region of Eastern China. The observational findings are confirmed by a suite of Weather Research and Forecasting (WRF)-Chem simulations that reveal the influences of increased aerosol levels and temperature through a complex chain of interactions among microphysical, dynamical, thermodynamic, and radiative processes.