Normalized difference haze index: a new spectral index for monitoring urban air pollution

Abstract

Haze is an undesirable meteorological and environmental phenomenon that can cause enormous harm to the environment, people's lives and health, and economic activities. This study focuses on Nanjing, Yangzhou and Suzhou in the lower reaches of the Yangtze River valley, China, which have suffered from the adverse effects of hazy weather in recent years. The spectral influence of haze on surface features was determined through analysis of the spectral variations of surface covers between hazy and haze-free days. On the basis of the established relationship, a new index called the normalized difference haze index (NDHI) was derived using moderate resolution imaging spectroradiometer (MODIS) data from winter 2008–2009. Correlation analysis of the derived NDHI with in situ observed PM₁₀ (particulate matter with diameter <10 μm) data reveals that NDHI over water bodies has a coefficient of 0.74, 0.57 and 0.67 with PM₁₀ for Nanjing, Yangzhou and Suzhou, respectively. It is concluded that NDHI is a reliable indicator of air pollution. It can be used as a new method of effectively monitoring air pollution from remotely sensed data.

Acknowledgements

We thank the two anonymous reviewers for their helpful comments. The data used in this study were acquired as part of NASA's Earth Science Enterprise. The algorithms were developed by the MODIS Science Teams. The data were processed by the MODIS Adaptive Processing System (MODAPS) and Goddard Distributed Active Archive Center (DAAC), and are archived and distributed by the Goddard DAAC. This research was funded by the National Science and Technology Support Plan of China (no. 2008BAC34B07). Additional funding was received from the Key Fundamental Research Projects of Natural Science in Universities affiliated with the Jiangsu Province (no. 08KJA170001), and the Key Short-term Projects of Inviting Overseas Experts to Universities affiliated with the Jiangsu Province, China.