Analysis of linear long-term trend of aerosol optical thickness derived from SeaWiFS using BAER over Europe and South China Institute of Environmental Physics, University of Bremen, Bremen, Germany
07 Dec 2011
Received: 17 Jun 2011 – Published in Atmos. Chem. Phys. Discuss.: 21 Jul 2011 Abstract. The main purposes of the present paper are not only to investigate linear
long-term trends of Aerosol Optical Thickness (AOT) at 443 and 555 nm over
regions in Europe and South China, but also to show the uncertainty caused
by cloud disturbance in the trend analysis of cloud-free aerosol. These
research areas are the densely urbanised and often highly polluted regions.
The study uses the Bremen AErosol Retrieval (BAER) and Sea-viewing Wide
Field-of-view Sensor (SeaWiFS) data for AOT retrievals in the specified
regions from October 1997 to May 2008. In order to validate the individually
retrieved AOTs and the corresponding trends, AErosol RObotic NETwork
(AERONET) level 2.0 data have been used. The retrieved AOTs were in good
agreement with those of AERONET (0.79 ≤ R ≤ 0.88, 0.08 ≤ RMSD ≤ 0.13). The contamination of the aerosol retrievals and/or AERONET
observations by thin clouds can significantly degrade the AOT and lead to
statistically non-representative monthly-means, especially during cloudy
seasons. Therefore an inter-correction method has been developed and
applied. The "corrected" trends for both BAER SeaWiFS and AERONET AOT were
similar and showed in average a relative difference of ∼25.19%.
In general terms, negative trends (decrease of aerosol loading) were mainly
observed over European regions, with magnitudes up to −0.00453 and
−0.00484 yr−1 at 443 and 555 nm, respectively. In contrast, the trend in Pearl
River Delta was positive, most likely attributed to rapid urbanization and
industrialization. The magnitudes of AOT increased by +0.00761 and +0.00625 yr−1
respectively at 443 and 555 nm.
Revised: 21 Nov 2011 – Accepted: 22 Nov 2011 – Published: 07 Dec 2011
Citation: Yoon, J., von Hoyningen-Huene, W., Vountas, M., and Burrows, J. P.: Analysis of linear long-term trend of aerosol optical thickness derived from SeaWiFS using BAER over Europe and South China, Atmos. Chem. Phys., 11, 12149-12167, doi:10.5194/acp-11-12149-2011, 2011.