Profiling transboundary aerosols over Taiwan and assessing their radiative effects

Abstract

A synergistic process was developed to study the vertical distributions of aerosol optical properties and their effects on solar heating using data retrieved from ground‐based radiation measurements and radiative transfer simulations. Continuous MPLNET and AERONET observations were made at a rural site in northern Taiwan from 2005 to 2007. The aerosol vertical extinction profiles retrieved from ground‐based lidar measurements were categorized into near‐surface, mixed, and two‐layer transport types, representing 76% of all cases. Fine‐mode (Ångström exponent, α , ∼1.4) and moderately absorbing aerosols (columnar single‐scattering albedo ∼0.93, asymmetry factor ∼0.73 at 440 nm wavelength) dominated in this region. The column‐integrated aerosol optical thickness at 500 nm ( τ 500nm ) ranges from 0.1 to 0.6 for the near‐surface transport type but can be doubled in the presence of upper layer aerosol transport. We utilize aerosol radiative efficiency (ARE, the impact on solar radiation per unit change of τ 500nm ) to quantify the radiative effects due to different vertical distributions of aerosols. Our results show that the ARE at the top of atmosphere (−23 W m −2 ) is weakly sensitive to aerosol vertical distributions confined in the lower troposphere. On the other hand, values of the ARE at the surface are −44.3, −40.6, and −39.7 W m −2 for near‐surface, mixed, and two‐layer transport types, respectively. Further analyses show that the impact of aerosols on the vertical profile of solar heating is larger for the near‐surface transport type than for the two‐layer transport type. The impacts of aerosol on the surface radiation and the solar heating profiles have implications for the stability and convection in the lower troposphere.