Abstract
Abstract. Obtaining continuous aerosol-optical-depth (AOD) measurements is a difficult task due to the cloud-cover problem. With the main motivation of overcoming this problem, an AOD-predicting model is proposed. In this study, the optical properties of aerosols in Penang, Malaysia were analyzed for four monsoonal seasons (northeast monsoon, pre-monsoon, southwest monsoon, and post-monsoon) based on data from the AErosol RObotic NETwork (AERONET) from February 2012 to November 2013. The aerosol distribution patterns in Penang for each monsoonal period were quantitatively identified according to the scattering plots of the Ångström exponent against the AOD. A new empirical algorithm was proposed to predict the AOD data. Ground-based measurements (i.e., visibility and air pollutant index) were used in the model as predictor data to retrieve the missing AOD data from AERONET due to frequent cloud formation in the equatorial region. The model coefficients were determined through multiple regression analysis using selected data set from in situ data. The calibrated model coefficients have a coefficient of determination, R2, of 0.72. The predicted AOD of the model was generated based on these calibrated coefficients and compared against the measured data through standard statistical tests, yielding a R2 of 0.68 as validation accuracy. The error in weighted mean absolute percentage error (wMAPE) was less than 0.40% compared with the real data. The results revealed that the proposed model efficiently predicted the AOD data. Performance of our model was compared against selected LIDAR data to yield good correspondence. The predicted AOD can enhance measured short- and long-term AOD and provide supplementary information for climatological studies and monitoring aerosol variation.
Highlights
Air quality issues in Asia can be attributed to unavoidable climate change impacts and the negative impact of anthropogenic activities arising from rapid population growth, industrialization and urbanization (IPCC, 2007, 2013)
During the southwest monsoon period (June–September), smoke emitted locally and from large-scale open burning activities in Sumatra, Indonesia is transported to Malaysia, yielding the highest Aerosol optical depth (AOD) at approximately 0.31–0.73
Seasonal variation in primary aerosol types and their physical characteristics at Penang, Malaysia are analyzed from February 2012 to November 2013
Summary
Air quality issues in Asia can be attributed to unavoidable climate change impacts and the negative impact of anthropogenic activities arising from rapid population growth, industrialization and urbanization (IPCC, 2007, 2013). Aerosol optical depth (AOD) derived from remote sensing has potential for assessing air quality. Many small-scale studies on the optical properties of aerosols have been conducted by Chew et al (2013), Mishra et al (2013), and Salinas et al (2013) using sun and sky scanning radiometers of AErosol RObotic NETwork (AERONET) (Holben et al, 1998). These methods are limited spatially relative to satellite imagery, and are complementary for comprehensive studies on atmospheric aerosols. To better monitor and understand aerosol variation, sufficient measurements and a practical observation paradigm of aerosols are necessary (Hansen et al, 1997; Tripathi et al, 2005; Kaskaoutis et al, 2007; Kaskaoutis and Kambezidis, 2008; Russell et al, 2010)
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