The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
A. M. De Frutos - One of the best experts on this subject based on the ideXlab platform.
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Morphological, chemical and optical absorbing characterization of aerosols in the Urban Atmosphere of Valladolid
Atmospheric Chemistry and Physics, 2005Co-Authors: S. Mogo, V. E. Cachorro, A. M. De FrutosAbstract:Samples of atmospheric aerosol particles were collected in Valladolid, Spain, during the winter of 2003-2004. The measurements were made with a Dekati PM10 cascade impactor with four size stages: greater than 10 µm, between 2.5 to 10 µm, 1 to 2.5 µm and less than 1 µm. The size and shape of the particles were analyzed with a scanning electron microscope (SEM) and elemental analysis was done with an energy dispersive x-ray analysis (EDX). We present an evaluation by size, shape and composition of the major particulate species in the Valladolid Urban Atmosphere. The total aerosol concentration is very variable, ranging from 39.86 µg·m-3 to 184.88 µg·m-3 with the coarse particles as the dominant mass fraction. Emphasis was given to fine particles (
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Morphological, chemical and optical absorbing characterization of aerosols in the Urban Atmosphere of Valladolid
Atmospheric Chemistry and Physics Discussions, 2005Co-Authors: S. Mogo, V. E. Cachorro, A. M. De FrutosAbstract:Aerosol samples were collected from the Valladolid (Spain) Atmosphere during 2003?2004 winter using a Dekati PM10 cascade impactor which allows to discriminate four level of particle sizes: greater than 10 µm, between 10 and 2.5, from 2.5 to 1 and less than 1 µm. The size and shape of the aerosol deposits were analyzed by means of individual particles through scanning electron microscope (SEM) technique. Additionally an energy dispersive X-ray analysis (EDX) was performed enabling elemental analysis of a large number of individual particles in a relatively short time. We present a classification in size, shape and composition of the major particulate species present in the Valladolid Urban Atmosphere. The aerosol concentration is very variable during winter, ranging from 39.86 µg·m?3 to 184.88 µg·m?3 with coarse particle as dominant fraction. Emphasize was given to fine particles, behind 1 µm, for which the visible (from 400 nm to 650 nm) light absorption coefficients were measured using the integrating plate technique. We have made some enhancements relative to the illumination system in the well known integrating plate method, for the absorption coefficients determination. The absorption coefficient ranges from 7.33×10?6 m?1 to 1.01×10?4 m?1 for the 550 nm wavelength. Its visible spectrum decreases with wavelength with greater slope for greater ? values.
Yoshizumi Kajii - One of the best experts on this subject based on the ideXlab platform.
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Examination on photostationary state of NOx in the Urban Atmosphere in Japan
Atmospheric Environment, 2006Co-Authors: Jun Matsumoto, Naohiro Kosugi, Ayaka Nishiyama, Ryoko Isozaki, Yasuhiro Sadanaga, Shungo Kato, Hiroshi Bandow, Yoshizumi KajiiAbstract:Abstract To investigate the photostationary state (PSS) of nitrogen oxides (NOx), fast and precise measurements of related compounds were simultaneously carried out in the Urban Atmosphere. A PSS parameter φ including the observed peroxy radical (ROx) was examined. Consequently, φ was not significantly different from unity in many cases. Observed NOx, O3, J NO 2 and ROx could reasonably elucidate the PSS of NOx. Meanwhile, in some cases with large ROx/O3, φ was significantly less than unity. It was suggested that the reaction rate coefficients of ROx with NO could be critical for the PSS in the Urban Atmosphere. It was confirmed that the LIF instrument is promising to observationally approach the PSS of NOx.
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In situ measurement of N2O5 in the Urban Atmosphere by thermal decomposition/laser-induced fluorescence technique
Atmospheric Environment, 2005Co-Authors: Jun Matsumoto, Naohiro Kosugi, Hidekazu Imai, Yoshizumi KajiiAbstract:Abstract The laser-induced fluorescence (LIF) detector with a thermal converter has been developed for measuring atmospheric N2O5. The detection limit for N2O5 was 11 pptv for 10-min averaging ( S / N = 2 , [NO2]=0). The field measurements of N2O5 were conducted in the Urban Atmosphere in winter. N2O5 was successfully monitored during four nights. Typically, observed N2O5 level was in the range of 0–200 pptv. Note that N2O5 reached 800 pptv at one night, when NOx level was extremely high and the temperature was low. After the data were selected by the stability of NOx, N2O5 chemistry was discussed for a representative case of the Urban night. Observed trend of N2O5 was compared with the theoretically predicted one. The heterogeneous loss rate of N2O5 on the aerosol surfaces was estimated as 5.2×10−4 s−1. Consequently, it was confirmed that N2O5 loss was critical for NOx budget in the Urban Atmosphere in winter, in comparison with NOx loss via NO3. The LIF instrument proved to be useful for studying nocturnal chemistry of N2O5 in the source region.
Jose L. Jimenez - One of the best experts on this subject based on the ideXlab platform.
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Concluding remarks: Faraday Discussion on chemistry in the Urban Atmosphere.
Faraday discussions, 2016Co-Authors: Jose L. JimenezAbstract:This article summarises the Concluding remarks from the Faraday Discussion on Chemistry in the Urban Atmosphere. The following themes are addressed: (a) new results that inform our understanding of the evolving sources and composition of the Urban Atmosphere (“News”); (b) results that identify gaps in our understanding that necessitate further work (“Gaps”); (c) the emerging instrumentation revolution and some of the challenges that it brings; (d) the structural issues of insufficient support for the analysis of field campaigns; and (e) some important areas that were missing from this Faraday Discussion and that should receive an increasing focus in the future.
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secondary organic aerosol formation from anthropogenic air pollution rapid and higher than expected
Geophysical Research Letters, 2006Co-Authors: Jose L. Jimenez, Rainer Volkamer, Federico San Martini, K Dzepina, Qi Zhang, D Salcedo, Luisa T MolinaAbstract:[1] The atmospheric chemistry of volatile organic compounds (VOCs) in Urban areas results in the formation of ‘photochemical smog’, including secondary organic aerosol (SOA). State-of-the-art SOA models parameterize the results of simulation chamber experiments that bracket the conditions found in the polluted Urban Atmosphere. Here we show that in the real Urban Atmosphere reactive anthropogenic VOCs (AVOCs) produce much larger amounts of SOA than these models predict, even shortly after sunrise. Contrary to current belief, a significant fraction of the excess SOA is formed from first-generation AVOC oxidation products. Global models deem AVOCs a very minor contributor to SOA compared to biogenic VOCs (BVOCs). If our results are extrapolated to other Urban areas, AVOCs could be responsible for additional 3–25 Tg yr−1 SOA production globally, and cause up to −0.1 W m−2 additional top-of-the-Atmosphere radiative cooling.
Maithili Sharan - One of the best experts on this subject based on the ideXlab platform.
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Surface layer turbulence spectra and dissipation rates during low winds in tropics
Boundary-Layer Meteorology, 1996Co-Authors: Anil Yadav, Sethu Raman, Maithili SharanAbstract:Spectral characteristics of surface layer turbulence in an Urban Atmosphere are investigated. The observations used for this purpose represent low wind conditions in the tropics. The normalized power spectral shapes exhibit the usual characteristics in the inertial subrange and obey Monin-Obukhov scaling. However, the low-frequency behaviours do not conform to the previous observed relations. For horizontal components, large energy is contained in the low frequencies in contrast to the vertical component where roll-off to zero frequency is faster. The turbulent kinetic energy dissipation rate estimated from the spectra using Kolmogorov's inertial subrange law is found to be isotropic unlike the velocity variances. The expressions for the dimensionless dissipation rate do not seem to work well in low winds in an Urban Atmosphere. For the data considered, the dissipation rate exhibits a power law relationship with the mean windspeed and the friction velocity.
Man-ting Cheng - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of formation rates of NO2 to gaseous and particulate nitrate in the Urban Atmosphere
Atmospheric Environment, 2007Co-Authors: Yu-chi Lin, Man-ting ChengAbstract:Abstract This work investigates the formation rates of gaseous and particulate nitrate in an Urban Atmosphere. This investigation is based on theoretical evaluations regarding potential NO2 oxidant reactions, leading to calculated values compared with field observations in Taichung City, Taiwan in 2002. The results show that the correlation coefficient (r) between the calculated value and field observation for HNO3 was 0.83 and that for NO 3 - was 0.66, suggesting that the theoretical calculations are suitable for assessing the formation rate of nitrate species. The 12-h average conversion rate of NO2 to HNO3 was approximately 3.4±3.1% h−1, while the formation rate of particulate NO 3 - was 2.4±1.8% h−1. Seasonal variations in gaseous and particulate production rates were obtained. The formation rate of HNO3 was found to be higher in summer, whereas the NO 3 - rate was lowest. The factors affecting the formation rate were also investigated using the model sensitivity test. The results showed that both HNO3 and NO 3 - were significantly dependent upon the ambient temperature and relative humidity in a moist Atmosphere.
