Retrieval of Aerosol Size Distribution from Microtops II Sunphotometer in Hong Kong

Kwon Ho Lee,Pak Wai Chan,Janet Nichol,Man Sing Wong

doi:10.4209/aaqr.2015.01.0048

Abstract

A new method has been developed for retrieving Aerosol Size Distribution (ASD) from spectral aerosol optical thickness (AOT) measured by Microtops II sunphotometer. The rationale of this method is based on a Spectral Extinction Fitting Technique (SEFT) between measured and model-simulated aerosol extinctions. Numerical simulation of aerosol extinctions includes seven aerosol microphysical properties and the resulting total of 64,324,260 datasets were used to compare with Microtops II sunphotometer AOT measurements at five wavelengths (340, 500, 675, 870, and 1020 nm). This SEFT method works directly on AOT measurements and does not require any specific inputs of aerosol properties. The accuracy was examined using AERONET inversion products, and the results show a difference between SEFT and AERONET inversion products of bimodal lognormal volume size concentrations, of ± 10%. The SEFT algorithm was applied for two specific conditions (hazy and clear atmospheres) in Hong Kong, and the corresponding ASD retrievals show reasonable agreements with AERONET inversion products.

Highlights

Aerosols are defined as particles suspended in the atmosphere in either liquid or solid form
A new method has been developed for retrieving Aerosol Size Distribution (ASD) from spectral aerosol optical thickness (AOT) measured by Microtops II sunphotometer
This may be caused by the errors from (i) different locations (AOT discrepancies caused by locational difference between three locations: Hong Kong International Airport (HKIA) and two AErosol RObotic NETwork (AERONET) sites), (ii) systematic errors in AOT measurements from two types of instruments (Microtops II and AERONET sunphotometers), and (iii) larger sized marine aerosols observed at HKIA than those observed at Hong Kong Hok Tsui (HKHT) and Hong Kong PolyU (HKPU) AERONET sites

Summary

INTRODUCTION

Aerosols are defined as particles suspended in the atmosphere in either liquid or solid form They have different size distributions, shapes and residence times, and are from different sources. Kassianov et al (2007) developed an alternative approach using combined direct and diffuse irradiance measurements for determining aerosol size distribution. This requires massive computational power and is time-consuming. Using the SEFT method, ASD retrieved from Microtops II hand-held sunphotometer measurements can be compared to the size distribution products from the AErosol RObotic NETwork (AERONET) database (http://aeronet.gsfc.nasa.gov) by sunphotometer measurements (Dubovik and King, 2000). The Hong Kong Hok Tsui AERONET is deployed on a remote peninsula near the coast for monitoring rural (background) aerosols

METHODOLOGY

Findings

DISCUSSION AND CONCLUSION