Abstract
Dry deposition of aerosols from the atmosphere is an important but
poorly understood and inadequately modeled process in atmospheric
systems for climate and air quality. Comparisons of currently used
aerosol dry deposition models to a compendia of published field
measurement studies in various landscapes show very poor agreement over
a wide range of particle sizes. In this study, we develop and test a new
aerosol dry deposition model that is a modification of the current model
in the Community Multiscale Air Quality (CMAQ) model. The new model
agrees much better with measured dry deposition velocities across
particle sizes. The key innovation is the addition of a second inertial
impaction term for microscale obstacles such as leaf hairs, microscale
ridges, and needleleaf edge effects. The most significant effect of the
new model is to increase the mass dry deposition of the accumulation
mode aerosols in CMAQ. Accumulation mode mass dry deposition velocities
increase by almost an order of magnitude in forested areas with lesser
increases for shorter vegetation. Peak PM2.5 concentrations are reduced
in some forested areas by up to 40% in CMAQ simulations. Over the
continuous United States, the new model reduced PM2.5 by an average of
16% for July 2018 at the Air Quality System monitoring sites. For
summer 2018 simulations, bias and error of PM2.5 concentrations are
significantly reduced, especially in forested areas.