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    The Dust-to-Gas Ratio, Size Distribution, and Dust Fall-Back Fraction of Comet 67P/Churyumov-Gerasimenko: Inferences From Linking the Optical and Dynamical Properties of the Inner Comae
    (2020-06-24)
    Marschall, Raphael
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    Markkanen, Johannes
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    Gerig, Selina-Barbara
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    Pinzon-Rodriguez, Olga
    ;
    Thomas, Nicolas
    In this work, we present results that simultaneously constrain the dust size distribution, dust-to-gas ratio, fraction of dust re-deposition, and total mass production rates for comet 67P/Churyumov-Gerasimenko. We use a 3D Direct Simulation Monte Carlo (DSMC) gas dynamics code to simulate the inner gas coma of the comet for the duration of the Rosetta mission. The gas model is constrained by ROSINA/COPS data. Further, we simulate for different epochs the inner dust coma using a 3D dust dynamics code including gas drag and the nucleus' gravity. Using advanced dust scattering properties these results are used to produce synthetic images that can be compared to the OSIRIS data set. These simulations allow us to constrain the properties of the dust coma and the total gas and dust production rates. We determined a total volatile mass loss of (6.1 +/- 1.5) center dot 10(9)kg during the 2015 apparition. Further, we found that power-laws withq=3.7-0.078+0.57are consistent with the data. This results in a total of5.1-4.9+6.0 center dot 109kg of dust being ejected from the nucleus surface, of which4.4-4.2+4.9 center dot 109kg escape to space and6.8-6.8+11 center dot 108kg (or an equivalent of14-14+22cm over the smooth regions) is re-deposited on the surface. This leads to a dust-to-gas ratio of0.73-0.70+1.3for the escaping material and0.84-0.81+1.6for the ejected material. We have further found that the smallest dust size must be strictly smaller than similar to 30 mu m and nominally even smaller than similar to 12 mu m.
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    Particle size distribution and anion content at a traffic site in Sha-Lu, Taiwan
    (2001-11-01)
    Chang, KF
    ;
    Fang, GC
    ;
    Lu, CS
    ;
    Bai, HL
    ;
    環境工程研究所
    Ambient air particle concentrations were sampled by two total suspended particle (TSP) samplers, PM10/PM2.5 specific sampler and micro-orifice uniform deposit impactor (MOUDI) during July-October 2000 at a traffic sampling site in central Taiwan. The average TSP concentration (194 mug/m(3)) was about a factor of two higher than that of the fraction <2.5 mum (93.2 mug/m(3)). The mean level of the fraction < 10 mum collected by MOUDI (93.2 mug/m(3)) was about 11/2 times higher than that of the size class <2.5 mum (43.8 mug/m(3)). Furthermore, this fraction showed a certain correlation with the TSP concentration. The particle size distribution was bimodal in the ambient air at the traffic site. The major peaks appear at particle diameters between 0.56-1.0 and 3.2-5.6 mum. The percentages of anions contained in TSP were 0.23% F-, 13.7% Cl-, 0.52% Br-, 12.0% NO3-, 18.9% NO2-, and 54.6% SO42-. The Cl-, NO2-, and NO3- size distributions were all unimodal and the major peaks appeared at 3.2-5.6 mum. The SO42- size distribution was bimodal, with major peaks at 0.32-0.56 and 3.2-5.6. (C) 2001 Elsevier Science Ltd. All rights reserved.
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    Estimation of PAHs dry deposition and BaP toxic equivalency factors (TEFs) study at Urban, Industry Park and rural sampling sites in central Taiwan, Taichung
    (2004-05-01)
    Fang, GC
    ;
    Chang, KF
    ;
    Lu, CS
    ;
    Bai, HL
    ;
    環境工程研究所
    The concentrations of polycyclic aromatic hydrocarbons (PAHs) in gas phase and particle bound were measured simultaneously at industrial (INDUSTRY), urban (URBAN), and rural areas (RURAL) in Taichung, Taiwan. And the PAH concentrations, size distributions, estimated PAHs dry deposition fluxes and health risk study of PAHs in the ambient air of central Taiwan were discussed in this study. Total PAH concentrations at INDUSTRY, URBAN, and RURAL sampling sites were found to be 1650 +/- 1240, 1220 +/- 520, and 831 +/- 427 ng/m(3), respectively. The results indicated that PAH concentrations were higher at INDUSTRY and URBAN sampling sites than the RURAL sampling sites because of the more industrial processes, traffic exhausts and human activities. The estimation dry deposition and size distribution of PAHs were also studied. The results indicated that the estimated dry deposition fluxes of total PAHs were 58.5, 48.8, and 38.6 mug/m(2)/day at INDUSTRY, URBAN, and RURAL, respectively. The BaP equivalency results indicated that the health risk of gas phase PAHs were higher than the particle phase at three sampling sites of central Taiwan. However, compared with the BaP equivalency results to other studies conducted in factory, this study indicated the health risk of PAHs was acceptable in the ambient air of central Taiwan. (C) 2004 Elsevier Ltd. All rights reserved.
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    Ground-based in situ measurements of near-surface aerosol mass concentration over Anantapur: Heterogeneity in source impacts
    (2013-01-01)
    Reddy, B. S. K.
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    Kumar, K. R.
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    Balakrishnaiah, G.
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    Gopal, K. R.
    ;
    Reddy, R. R.
    Surface measurements of aerosol physical properties were made at Anantapur (14.62A degrees N, 77.65A degrees E, 331 m a.s.l), a semiarid rural site in India, during August 2008-July 2009. Measurements included the segregated sizes of aerosolsas as well as total mass concentration and size distributions of aerosols measured at low relative humidity (RH < 75%) using a Quartz Crystal Microbalance (QCM) in the 25-0.05 mu m aerodynamic diameter range. The hourly average total surface aerosol mass concentration in a day varied from 15 to 70 mu g m(-3), with a mean value of 34.02 +/- 9.05 mu g m(-3) for the entire study period. A clear diurnal pattern appeared in coarse, accumulation and nucleation-mode particle concentrations, with two local maxima occurring in early morning and late evening hours. The concentration of coarse-mode particles was high during the summer season, with a maximum concentration of 11.81 +/- 0.98 mu g m(-3) in the month of April, whereas accumulationmode concentration was observed to be high in the winter period contributed > 68% to the total aerosol mass concentration. Accumulation aerosol mass fraction, A (f) (= M (a)/M (t)) was highest during winter (mean value of A (f) 0.80) and lowest (A (f) 0.64) during the monsoon season. The regression analysis shows that both R (eff) and R (m) are dependent on coarse-mode aerosols. The relationship between the simultaneous measurements of daily mean aerosol optical depth at 500 nm (AOD(500)) and PM2.5 mass concentration ([PM2.5]) shows that surface-level aerosol mass concentration increases with the increase in columnar aerosol optical depth over the observation period.