Satellite-based evidence of wavelength-dependent aerosol absorption in biomass burning smoke inferred from Ozone Monitoring Instrument

Abstract

Abstract. We provide satellite-based evidence of the spectral dependence of absorption in biomass burning aerosols over South America using near-UV measurements made by the Ozone Monitoring Instrument (OMI) during [2005][2006][2007]. In the current near-UV OMI aerosol algorithm (OMAERUV), it is implicitly assumed that the only absorbing component in carbonaceous aerosols is black carbon whose imaginary component of the refractive index is wavelength independent. With this assumption, OMI-derived aerosol optical depth (AOD) is found to be significantly over-estimated compared to that of AERONET at several sites during intense biomass burning events (August-September). Other wellknown sources of error affecting the near-UV method of aerosol retrieval do not explain the large observed AOD discrepancies between the satellite and the ground-based observations. A number of studies have revealed strong spectral dependence in carbonaceous aerosol absorption in the near-UV region suggesting the presence of organic carbon in biomass burning generated aerosols. A sensitivity analysis examining the importance of accounting for the presence of wavelength-dependent aerosol absorption in carbonaceous particles in satellite-based remote sensing was carried out in this work. The results convincingly show that the inclusion of spectrally-dependent aerosol absorption in the radiative transfer calculations leads to a more accurate characterization of the atmospheric load of carbonaceous aerosols. The use of a new set of aerosol models assuming wavelength-dependent aerosol absorption in the near-UV region (Absorption Angstrom Exponent λ −2.5 to −3.0 ) improved the OMAERUV retrieval results by significantly Correspondence to: H. Jethva (hiren.jethva@hamptonu.edu) reducing the AOD bias observed when gray aerosols were assumed. In addition, the new retrieval of single-scattering albedo is in better agreement with those of AERONET within the uncertainties ( SSA = ±0.03). The new colored carbonaceous aerosol model was also found to reproduce the ground-based AOD observations over the biomass burning region of central Africa and northern India. Together with demonstrating a significant improvement in the retrieval of aerosol properties from OMI, the present study highlights the greater sensitivity of the near-UV measurements to the varying spectral aerosol absorption. This capability can be explored further for the use in the identification of the black carbon and organics in the biomass burning aerosols.

Interpretation of FRESCO cloud retrievals in case of absorbing aerosol events

“…The first biomass burning aerosol model was taken from De Graaf et al (2012) (called Case 1), which represents aged smoke. The absorptionÅngström exponent was 2.91 in the UV, which is in good agreement with the values reported by Jethva and Torres (2011). This aerosol model represents a strongly absorbing aerosol case, having a single scattering albedo of 0.82 at 380 nm.…”

AERONET-based models of smoke-dominated aerosol near source regions and transported over oceans, and implications for satellite retrievals of aerosol optical depth

“…Jethva and Torres, 2011), and is strongly dependent on composition, with black carbon having a roughly spectrally neutral refractive index but absorption of organic carbon increasing at shorter visible and UV wavelengths (Bond, 2001;Kirchstetter et al, 2004, Andreae andGelencsér, 2006;Lewis et al, 2008). As such the spectral dependence of UV AOD and absorption, as in the visible, may show strong variations dependent on combustion phase and fuel type (e.g.…”

Light absorption of brown carbon aerosol in the PRD region of China

“…South and East Asia are typical regions of atmospheric brown clouds (ABC) (Alexander et al, 2015). Biomass burning has been recognized as a significant contributor to ABC, including forest burning, crop waste burning, traditional religious activities and residential burning in countries like India, China and Thailand (Venkataraman et al, 2006;Yan et al, 2006;mainly absorbs light at UV and short-visible wavelengths (Chen and Bond, 2010;Kirchstetter et al, 2004;Lewis et al, 2008;Sandradewi et al, 2008;Schmid et al, 2006) and this strong spectral dependence has aroused more and more interest recently (Feng et al, 2013;Bahadur et al, 2012;Chung et al, 2012b;Wang et al, 2014;Jethva and Torres, 2011). BrC was ever estimated to contribute about 10-30 % of total absorption of fine particles at shorter wavelengths, e.g.…”