Diurnal variability of dust aerosol optical thickness and Angström exponent over dust source regions in China

Using 22 months of Sunphotometer Aerosol Optical Thickness (AOT) data collected near the Taklamakan and Gobi dust source regions (Dunhuang, 40.09°N, 94.41°E) in China; we examine the diurnal and seasonal change of dust aerosol properties. Most dust events are during the spring through early summer months with a season-invariant diurnal change of more than ±10% for AOT and ±30% for Angstro ¨m exponent, with larger AOT and smaller Angstro expönent values late in the afternoon. These values are much larger when compared to recent studies that have reported a much smaller (±5%) diurnal variability of dust AOT over various AERONET sites where dust is a major contributor to AOT. The differences are largely due to the geographical locations and meteorological conditions and such large diurnal changes of aerosol properties at or near dust source regions may be significant enough for consideration in regional radiative forcing, air quality and numerical modeling studies.