In situ aerosol optics in Reno, NV, USA during and after the summer 2008 California wildfires and the influence of absorbing and non-absorbing organic coatings on spectral light absorption

Abstract

Abstract. Hundreds of wildfires in Northern California were sparked by lightning during the summer of 2008, resulting in downwind smoke for the months of June and July. Comparisons are reported for aerosol optics measurements in Reno, Nevada made during the very smoky month of July and the relatively clean month of August. Photoacoustic instruments equipped with integrating nephelometers were used to measure aerosol light scattering and absorption coefficients at wavelengths of 405 nm and 870 nm, revealing a strong variation of aerosol light absorption with wavelength. Insight on fuels burned is gleaned from comparison ofÅngström exponents of absorption (AEA) versus single scattering albedo (SSA) of the ambient measurements with laboratory biomass smoke measurements for many fuels. Measurements during the month of August, which were largely unaffected by fire smoke, exhibit surprisingly low AEA for aerosol light absorption when the SSA is highest, again likely as a consequence of the underappreciated wavelength dependence of aerosol light absorption by particles coated with nonabsorbing organic and inorganic matter. Coated sphere calculations were used to show that AEA as large as 1.6 are possible for wood smoke even with non-absorbing organic coatings on black carbon cores, suggesting care be exercised when diagnosing AEA.

The Multi-Wavelength Absorption Analyzer (MWAA) Model as a Tool for Source and Component Apportionment Based on Aerosol Absorption Properties: Application to Samples Collected in Different Environments

“…These samples were the same providing the two lowest values for α BrC (Figure 7). This suggests that these samples are impacted by different sources/processes modifying the optical characteristics compared to the others (e.g., [52]); for this reason, they will be excluded by the following statistics. As far as OC FF , OC WB , and OC NC are concerned, they contributed 40% ± 14%, 48% ± 14%, and 12% ± 4% to the OC, respectively (average ± standard deviation).…”

“…In this work α BC = 1 was set according to expectancies for pure, small BC spheres (e.g., [3]) as often applied in the literature (e.g., [51]). Nevertheless, different choices can be in principle be performed due to the possible effect of BC core and coating sizes on the Ångström absorption exponent (e.g., [52]). …”

Synergistic Approach for the Aerosol Monitoring and Identification of Types over Indo-Gangetic Basin in Pre-Monsoon Season

“…7 (Bergstrom et al, 2004). Relatively lower values of AAE (0.7-1.3) and EAE (0.45-0.76) indicates the presence of black carbon (BC) coated dust/sea-salt particles in Type II aerosols (Gyawali et al, 2009). BC coating over dust particles (core-shell mixing) have been seen as most probable state of mixing during the PrM season over the IGB Srivastava and Ramachandran, 2012).…”

Optical and microphysical properties of natural mineral dust and anthropogenic soil dust near dust source regions over Northwestern China

“…However, we note that the actual AAE of BC can be greater or less than 1, as this value is highly dependent on the internal/external core size and its ageing process (Gyawali et al, 2009). …”