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131.
Uhrner U Zallinger M von Löwis S Vehkamäki H Wehner B Stratmann F Wiedensohler A 《Journal of the Air & Waste Management Association (1995)》2011,61(4):399-408
A major source of particle number emissions is road traffic. However, scientific knowledge concerning secondary particle formation and growth of ultrafine particles within vehicle exhaust plumes is still very limited. Volatile nanoparticle formation and subsequent growth conditions were analyzed here to gain a better understanding of "real-world" dilution conditions. Coupled computational fluid dynamics and aerosol microphysics models together with measured size distributions within the exhaust plume of a diesel car were used. The impact of soot particles on nucleation, acting as a condensational sink, and the possible role of low-volatile organic components in growth were assessed. A prescribed reduction of soot particle emissions by 2 orders of magnitude (to capture the effect of a diesel particle filter) resulted in concentrations of nucleation-mode particles within the exhaust plume that were approximately 1 order of magnitude larger. Simulations for simplified sulfuric acid-water vapor gas-oil containing nucleation-mode particles show that the largest particle growth is located in a recirculation zone in the wake of the car. Growth of particles within the vehicle exhaust plume up to detectable size depends crucially on the relationship between the mass rate of gaseous precursor emissions and rapid dilution. Chassis dynamometer measurements indicate that emissions of possible hydrocarbon precursors are significantly enhanced under high engine load conditions and high engine speed. On the basis of results obtained for a diesel passenger car, the contributions from light diesel vehicles to the observed abundance of measured nucleation-mode particles near busy roads might be attributable to the impact of two different time scales: (1) a short one within the plume, marked by sufficient precursor emissions and rapid dilution; and (2) a second and comparatively long time scale resulting from the mix of different precursor sources and the impact of atmospheric chemistry. 相似文献
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The Science of Nature - 相似文献
137.
Ulrich Struck Maren Voss Bodo von Bodungen Nicolai Mumm 《Die Naturwissenschaften》1998,85(12):597-603
15 N of bulk sediment, organic carbon concentrations, and abundances of exoskeletons of Bosmina
longispina
maritima in the sediment, the data are used to evaluate significant sources of nitrogen in the food web over the past century. Nitrogen
isotopic composition of bulk sediments ranges from 2.5 to 4.5?, that of exokeletons varies between 0.4 and 6.2?. The two are
positively correlated. A marked increase in the abundance of Bosmina since 1965 (from less than 500 specimen to more than 5000 specimen cm3 of sediment) is correlated with a significant increase in sedimentary organic carbon concentrations (from 4% to more than
10%). The isotopic data do not identify increased land-derived nitrate as the dominant nitrogen source fuelling the increase.
Instead, we postulate that nitrogen fixation by diazotrophic bacteria has been one of the larger sources of nitrogen in the
Baltic Sea, as it is today.
Received: 29 April 1998 / Accepted in revised form: 13 August 1998 相似文献
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