Aerosol optical thickness over Pearl River Delta region, China

ABSTRACT

We validated moderate resolution imaging spectroradiometer (MODIS) Level 2 aerosol products with ground-based sun photometer (CE-318) measurements over the Pearl River Delta (PRD) region. MODIS aerosol products are also used to investigate the temporal and spatial variations of aerosol optical thickness (AOT). The results show that MODIS AOT is validated quantitatively with a higher correlation coefficient (r = 0.88, 0.80 at Guangzhou and r = 0.95, 0.92 at Hong Kong) and lower root mean square errors (RMSE = 0.15, 0.16 at Guangzhou and RMSE = 0.07, 0.08 at Hong Kong), while the Ångström exponent (α) is still in doubt (r = 0.09). The MODIS AOT values are generally higher than those of the CE-318 values in Guangzhou and smaller than those in Hong Kong. The regional multi-year monthly (July 2002–December 2012) mean AOT values are 0.66 ± 0.20 and 0.64 ± 0.18 for Terra- and Aqua-MODIS, respectively. From month to month, the values of Terra-MODIS AOT are larger than those of Aqua-MODIS during most of the month. This implies that AOT in the morning is generally larger than that in the afternoon. The largest monthly AOT occurred in April at 0.85 ± 0.16 and 0.88 ± 0.17 for Terra-MODIS and Aqua-MODIS, respectively, and the smallest occurred in November for both Terra- and Aqua-MODIS at 0.47 ± 0.13 and 0.47 ± 0.10, respectively. The spatial distribution of AOT in spring and summer shows more variation than in autumn and winter. This can be partially attributed to the cleansing effect of precipitation which clears aerosol particles over the whole region in spring and summer and results in a lower AOT outside urban areas, while AOT in urban areas is higher where anthropogenic aerosols build up quickly despite the cleansing effect of the rain.

KEYWORDS:

• aerosol optical thickness
• Ångström exponent
• Pearl River Delta
• MODIS
• sun photometer

Acknowledgements

The authors thank NASA/MODIS (http://modis.gsfc.nasa.gov) for providing aerosol products; Surface wind fields data obtained from Earth System Research Laboratory (ESRL). Ground-based aerosol product in Hong Kong was obtained from AERONET.

Additional information

Funding

This work was supported partially by the Scientific Research Foundation of Jimei University [Grant Number: 201211290001], The Foundation of Pan Jinlong [Grant Number: ZC2013022], the Education Department of Fujian Province Science and Technology Project [Grant Number: JA14183], the NSF China Major Program [Grant Numbers: 61190114 and 41171324], The State Key Fundamental Science Funds of China [Grant Numbers: 2011CB302705, 2010CB950702, and 2010CB428503], The Funds for Ph.D. Education [Grant Number: 20110091110028], The Fundamental Research Project of MOST [Grant Number: 2005DKA32300], and The Priority Academic Program Development of Jiangsu Higher Education Institutions, Zhejiang Province Key Science and Technology Innovation Team [Grant Number: 2010R50030].