Estimate of aerosol absorbing components of black carbon, brown carbon, and dust from ground-based remote sensing data of sun-sky radiometers

Black carbon (BC), brown carbon (BrC), and mineral dust (DU) are three major light absorbing aerosols, playing important roles in climate change. Better knowledge of their concentrations is necessary for more accurate estimates of their radiative forcing effects of climate. We present a method to retrieve columnar contents of BC, BrC, and DU simultaneously from spectral refractive indices and spectral single scattering albedo obtained from the sun-sky radiometer measurements. Then, this method is applied to investigate the columnar volume fractions and mass concentrations of BC, BrC, and DU in Beijing, China, based on measurements obtained from 2009 to 2010. Results show that among the three absorbing aerosols, DU dominates the largest volume fraction in the total aerosol volume (20-45%), followed by BrC (5-25%), and BC (< 5%). The retrieved monthly mean content of each absorbing component exhibits clear seasonal variation. BrC dominates in late fall and winter (40-92.5 mg/m(2)), whereas is extremely low in summer (< 10 mg/m(2)). DU dominates in spring, ranging from 270 to 405 mg/m(2) (with volume fraction >30%), while during June-September, the DU fraction is generally lower than 30%. BC is characterized by low levels throughout the year. The monthly mean BC columnar mass concentration ([BC]) ranges from 2.7 to 7.3 mg/m(2) with winter slightly higher than other seasons. As a preliminary validation, we compare our retrieved [BC] with in situ measurements. Similar day-to-day variation trends and good correlations are found between the retrieved [BC] and in situ measurements.