Combining Multi-Wavelength AERONET SSA Retrievals with a MIE Model to
Quantify the Size of Absorbing Aerosols and the In-Situ Lifetime of
Sulfate
Abstract
Energy, transport, urbanization and burning are responsible for changes
in atmospheric BC. This work uses direct solar atmospheric column
measurements of single scatter albedo [SSA] retrieved at multiple
wavelengths from AERONET at 68 Asian sites over 17 years. A MIE model is
solved across the wavelengths using a core-shell mixing approximation to
invert the probabilistic BC, shell size, and UV SSA. Orthogonal patterns
are obtained for urban, biomass burning [BB], and long-range
transport [LRT] conditions, which are used to analyze and attribute
source types of BC across the region. Large urban areas (thought to be
dominated by urban BC) are observations during targeted times (shorter
than seasonally) to yield significant contributions from non-urban BC.
BB and LRT are observed to dominate Beijing and Hong Kong 2 months a
year. LRT is observed during the clean Asian Monsoon season in both
Nepal and Hong Kong, with sources identified from thousands of
kilometers away. Computing the shift in shell size required to constrain
the results approximates secondary aerosol growth in-situ, and
subsequently aerosol lifetime, which is found to range from 11 days to a
month, implying both a significant amount of BC above the boundary
layer, and that BC generally has a longer lifetime than PM2.5. These
findings are outside of the range of most modeling studies focusing on
PM2.5, but are consistent with independent measurements from SP2 and
modeling studies of BC that use core-shell mixing together with high BC
emissions.