Abstract
Observations from Aerosol Robotic Network (AERONET) radiometers during 2003–2012 in Beijing are assessed and used to characterize a series of aerosol properties and their variations. Some distinctive features are found. (1) Aerosol optical depth contributed by fine particles at 440 nm (AOD440-F) in spring showed a decreasing trend in the decade; compared with 2003 it decreased about 54 % in the spring of 2012. The annual averaged AOD440-F increased from 2003 to 2007 and decreased after Beijing Olympics (2008). (2) The spectrum of single-scattering albedo (SSA) followed a rapid increasing pattern from 440 to 675 nm and a slow decreasing or neutral pattern from 675 to 1020 nm, but in summer it was nearly wavelength independent. After Beijing Olympics, in addition to summer in which the SSA remained almost unchanged, in the other seasons the SSA increased, this suggests the decline of absorbing aerosols loading. (3) The imaginary part of aerosol refractive indices k(λ) showed a wintertime maximum and summertime minimum associated with the variation of black carbon content. After Beijing Olympics k(λ) significantly decreased. A good correlation between k(λ) and SSA was observed. However, different from the electromagnetic theory predicted, high (low) real part n(λ) sometimes corresponded to low (high) SSA. (4) The volume median radius of fine mode (Rvf) and aerosol optical depth (AOD) showed a good correlation, but the volume median radius of coarse mode (Rvc) and AOD exhibited a minor and negative correlation which different from previous studies.
Published Version
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