Wavelength dependence of aerosol optical depth and the fit of the �ngstr�m law

Adeyewa, Zechariah Debo; Balogun, E. E.

doi:10.1007/s00704-002-0707-3

Cited by 42 publications

(27 citation statements)

References 29 publications

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“…Our data reveal an inverse relationship between α and β values, i.e. the low exponent α values are associated with the high β values and vice-versa, which agrees with earlier observations by Adeyewa and Balogun (2003), Dani et al (2003), and Satheesh et al (2006). The correlation coefficient between α and β is estimated and shown in Fig.…”

Section: Monthly Variation Of åNgström Parameters α and βsupporting

confidence: 91%

“…The attenuation of solar radiation by aerosol particles is strongly dependent on the size of the particle and wavelength interval considered. Therefore, investigations of the spectral variation of aerosol attenuation within the near UV, visible and near infrared regions could be very informative (Adeyewa and Balogun, 2003). We have selected wavelengths of 380, 440, 500, 675, 870 and 1020 nm for studying spectral variation of aerosol properties, and 936-nm wavelength for the precipitable water vapor study.…”

Section: Site and Instrumentationmentioning

confidence: 99%

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Spectral Variation of Total Column Aerosol Optical Depth over Rajkot: A Tropical Semi-arid Indian Station

Ranjan

Joshi

Iyer

2007

Aerosol Air Qual. Res.

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in winter. The summer increase is found to be due to the high wind speed producing larger amounts of wind-driven dust particles. The winter AOD values decrease more at higher wavelengths, indicating a general reduction in the number of bigger particles. Also during the winter months the wind direction changed to southerly and southeasterly bringing air from more rural areas to the measurement site. The amplitude of the observed high AOD values in summer is higher (low during winter) for longer wavelengths, which shows that coarse particles contribute more to the observed variation as compared to sub-micron particles. To characterize the aerosol optical depths, the Ångström parameters α and β were used.

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Section: Monthly Variation Of åNgström Parameters α and βsupporting

confidence: 91%

Section: Site and Instrumentationmentioning

confidence: 99%

Spectral Variation of Total Column Aerosol Optical Depth over Rajkot: A Tropical Semi-arid Indian Station

Ranjan

Joshi

Iyer

2007

Aerosol Air Qual. Res.

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“…Generally, the AOD decreased in contrast to an increase in wavelength, especially on HPDs. This dependence of the AOD on wavelength is consistent with other research, e.g., Adeyewa and Balogun [43] and Wang et al [44].The AOD on HPDs was evidently larger than those on NHPDs. The mean magnitudes of AOD 500 nm on HPDs were about 3.7 and 1.6 times greater than those on NHPDs in Beijing and Xuzhou, respectively.…”

Section: Aod and åNgström Exponentsupporting

confidence: 82%

Haze Optical Properties from Long-Term Ground-Based Remote Sensing over Beijing and Xuzhou, China

Qin

Wang

et al. 2018

Remote Sensing

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Aerosol haze pollution has had a significant impact on both global climate and the regional air quality of Eastern China, which has a high proportion of high level pollution days. Statistical analyses of aerosol optical properties and direct radiative forcing at two AERONET sites (Beijing and Xuzhou) were conducted from 2013 to 2016. Results indicate: (1) Haze pollution days accounted for 26% and 20% of days from 2013 to 2016 in Beijing and Xuzhou, respectively, with the highest proportions in winter; (2) The averaged aerosol optical depth (AOD) at 550 nm on haze days were about 3.7 and 1.6 times greater than those on clean days in Beijing and Xuzhou, respectively. At both sites, the maximum AOD occurred in summer; (3) Hazes were dominated by fine particles at both sites. However, as compared to Xuzhou, Beijing had larger coarse mode AOD and higher percentage of small α. This data, together with an analysis of size distribution, suggests that the hazes in Beijing were more susceptible to coarse dust particles than Xuzhou; (4) During hazes in Beijing, the single scattering albedo (SSA) is significantly higher when compared to clean conditions (0.874 vs. 0.843 in SSA 440 nm ), an increase much less evident in Xuzhou. The most noticeable differences in both SSA and the imaginary part of the complex refractive index between Beijing and Xuzhou were found in winter; (5) In Beijing, the haze radiative forcing produced an averaged cooling effect of −113.6 ± 63.7 W/m 2 at the surface, whereas the averaged heating effect of 77.5 ± 49.7 W/m 2 within the atmosphere was at least twice as strong as clean days. In Xuzhou, such a radiative forcing effect appeared to be much smaller and the difference between haze and clean days was insignificant. Derived from long-term observation, these findings are more significant for the improvement of our understanding of haze formation in China and the assessment of its impacts on radiative forcing of climate change than previous short-term case studies.

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“…Different α values determined in various spectral bands have been reported by various authors (Eck et al 1999;Reid et al 1999). In some cases negative α values have also been obtained (Cachorro et al 2001;Adeyewa and Balogun 2003) when its determination takes place in the visible (VIS) and near-infrared spectrum. TheÅngström exponent can be related to the Junge power law (Junge 1955):…”

Section: Theoretical Backgroundmentioning

confidence: 99%

Investigation into the wavelength dependence of the aerosol optical depth in the Athens area

Kaskaoutis

Kambezidis

2006

Quart J Royal Meteoro Soc

107

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SUMMARYGround-based solar spectral irradiance measurements obtained by a spectroradiometer have been used to retrieve the aerosol optical depth, τ α , and theÅngström wavelength exponent, α. These measurements were obtained in the Athens centre in May 1995. Exponent α is frequently computed from spectral measurements both from ground-based photometers and satellite remote sensing retrievals. Although the retrieval of α has been the subject of many studies worldwide, its spectral variation is typically not considered. In this study we analyse the spectral measurements of ln τ α versus ln λ, where λ is the wavelength, at six selected wavelengths which cover the spectrum from 340 to 870 nm. It is obvious that there is significant curvature in the ln τ α versus ln λ relationship, and the reasons for this are examined. It was found that this curvature depends on both atmospheric turbidity and aerosol optical properties, and a second order polynomial fit provides excellent agreement. The curvature of the polynomial equation becomes greater as the aerosol loading alters from high to low. The curvature is characterized by the second derivative of α, which can be utilized in conjunction with α to characterize the spectral dependence of aerosol optical depth, and can also be used as an indicator of the relative influence of fineversus coarse-mode particles.

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Wavelength dependence of aerosol optical depth and the fit of the �ngstr�m law

Cited by 42 publications

References 29 publications

Spectral Variation of Total Column Aerosol Optical Depth over Rajkot: A Tropical Semi-arid Indian Station

Spectral Variation of Total Column Aerosol Optical Depth over Rajkot: A Tropical Semi-arid Indian Station

Haze Optical Properties from Long-Term Ground-Based Remote Sensing over Beijing and Xuzhou, China

Investigation into the wavelength dependence of the aerosol optical depth in the Athens area

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