8 research outputs found
Spectral- and size-resolved mass absorption efficiency of mineral dust aerosols in the shortwave spectrum: a simulation chamber study
Get PDFThis paper presents new laboratory measurements
of the mass absorption efficiency (MAE) between 375 and
850 nm for 12 individual samples of mineral dust from different
source areas worldwide and in two size classes: PM10:6
(mass fraction of particles of aerodynamic diameter lower
than 10.6 \u3bcm) and PM2:5 (mass fraction of particles of aerodynamic
diameter lower than 2.5 \u3bcm). The experiments were
performed in the CESAM simulation chamber using mineral
dust generated from natural parent soils and included optical
and gravimetric analyses.
The results show that the MAE values are lower for
the PM10:6 mass fraction (range 37\u2013135x10-3 m2 g-1 at
375 nm) than for the PM2:5 (range 95\u2013711x10-3 m2 g-1 at
375 nm) and decrease with increasing wavelength as lambda-AAE,
where the \uc5ngstr\uf6m absorption exponent (AAE) averages
between 3.3 and 3.5, regardless of size. The size independence
of AAE suggests that, for a given size distribution, the oxide fraction, which could ease the application and the validation
of climate models that now start to include the representation
of the dust composition, as well as for remote
sensing of dust absorption in the UV\u2013vis spectral region
Production of particulate brown carbon during atmospheric aging of residential wood-burning emissions
Get PDFWe investigate the optical properties of light-absorbing organic carbon
(brown carbon) from domestic wood combustion as a function of simulated
atmospheric aging. At shorter wavelengths (370–470 nm), light absorption by
brown carbon from primary organic aerosol (POA) and secondary organic
aerosol (SOA) formed during aging was around 10 % and 20 %,
respectively, of the total aerosol absorption (brown carbon plus black
carbon). The mass absorption cross section (MAC) determined for black carbon
(BC, 13.7 m2 g−1 at 370 nm, with geometric standard deviation GSD =1.1) was consistent with that
recommended by Bond et al. (2006). The corresponding MAC of POA
(5.5 m2 g−1; GSD =1.2) was higher than that of SOA
(2.4 m2 g−1; GSD =1.3) at 370 nm. However, SOA presents a
substantial mass fraction, with a measured average SOA ∕ POA mass ratio
after aging of ∼5 and therefore contributes significantly to the
overall light absorption, highlighting the importance of wood-combustion SOA
as a source of atmospheric brown carbon. The wavelength dependence of POA and
SOA light absorption between 370 and 660 nm is well described with
absorption Ångström exponents of 4.6 and 5.6, respectively.
UV-visible absorbance measurements of water and methanol-extracted OA were
also performed, showing that the majority of the light-absorbing OA is water
insoluble even after aging.</p
An experimental study of the role of biodiesel on the performance of diesel particulate filters
No full textInternational audienceThe study investigates the impact of the physical properties of biodiesel particulate matter on the performance of diesel particulate filters (DPF). Filtration efficiency (FE) and pressure drop (PD), as a function of loading time, were studied on a DPF for a range of biodiesel fuels with varying fuel molecular oxygen content from 0% (diesel) to 14%. The change in the oxygen content of the fuel resulted in diesel particle matter (DPM) with significantly different physical properties. FE and PD were investigated during the deep bed filtration stage, chosen because it presents the start of the loading process, which is a crucial step for high performance filtration. Firstly, we investigated the influence of the size distribution of various particles on the deep bed filtration, wherein size distributions of PM were measured before and after the DPF. The results show that for all fuels the FE is higher for smaller particles, as diffusion is the dominant process governing the filtration in tested conditions. Further we found that FE for biodiesel particles were up to 10% lower than for diesel particles at the beginning of the loading process, but with that difference diminishing as the filter fully loads. This result is attributed to the increase in the particulate fractal dimension with a higher biodiesel fraction resulting in more compact particles with lower diffusion coefficients. In addition, the study also demonstrated that the change of FE during the loading process is dependent on the physical properties of DPM. DPF performs differently for biodiesel soot as compared to diesel soot, with biodiesel soot causing higher PD for the same mass of the soot loaded on the DPF. This effect was attributed to the smaller primary particulate size of the biodiesel particles. The results presented in this study will further facilitate understanding of the filtration processes of particulate matter and validate detailed filtration models for the prediction of the filtration efficiency (FE) and pressure drop (PD) depending on the particle morphological properties
Computationally simple lattice methods for option and bond pricing
No full textRecombining lattices, Option pricing, Discrete-time models, C63,
