AIR POLLUTION – MONITORING MODELLING AND HEALTH

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62 Air Pollution – Monitoring, Modelling and Health the gas concentration of O 3, NO 2 , NO, and SO 2 integrated along a light path of 391 m. More experimental details are described in Saiz-Lopez et al., 2006 and only a brief description is made. The system used in this study consists of an emitter (EM 150) and receiver (RE 150) in combination with the AR 500 analyzer. The emitter was located on the roof of the School of Agricultural Studies about 16m above the ground, and the receiver system was installed 12m above street level, on a terrace on the School of Computing Science. The average altitude of the optical path was 14m above ground level. The 391m light beam crosses over a small parking area and is nearby two interior city roads containing the heaviest traffic in the city. Also, a monitoring station of the National Meteorological Institute was located in the middle of the light path and provided surface meteorological data for the interpretation of the measurements in this study. In the evaluation procedure (Platt, 1994; Plane and Saiz-Lopez, 2005), the wavelength region of the strongest absorption was used for each gas: 200–250 nm (NO), 250–300 nm (O 3 ), 360–440 nm (NO 2 ) and 260–340 nm (SO 2 ). The calibration of the DOAS system was made using the cell reference system provided by the manufacturer (an OPSISCB100 calibration bench with cells of various lengths, a calibration lamp CA 150 and an OPSIS OC 500 ozone calibrator unit). For the pollutants monitored, the manufacturer specifies a detection limit of the order of 1 μg m −3 and an accuracy of 2% for NO 2 , SO 2 and O 3 and 3%–15% for NO. 2.2.2 Passive sampling technique Passive samplers are based on free flow (according to the Fick’s first law of diffusion) of pollutant molecules from the sampled medium to a collecting medium. These devices can be deployed virtually anywhere, being them useful for mean concentrations determinations. Radiello® samplers (Fondazione Salvatore Maugeri, Padova, Italy) have been employed to measure ambient NO 2 and ozone concentrations. Radiello passive samplers are different from the axial ones because the diffusion process is radial through a microporous cylinder in which a cartridge with adsorbent material is positioned. Consequently, there is a greater diffusion area, which facilitates the reaction between the gas and the collection cartridge (Cocheo et al., 1999), giving an uptake rate of at least two times higher. Radiello passive samplers were used to describe the evolution of NO 2 and O 3 levels in the urban air of Ciudad Real throughout the four seasonal periods during 2007. The Radiello sampler for measuring nitrogen dioxide and O 3 is based on the principle that NO 2 and O 3 diffuse across the diffusive body towards the absorbing material on the inner cartridge. NO 2 and O 3 in the atmosphere are captured in the sampler as nitrite (NO 2 −) and 4- pyridylaldehyde, respectively. According to the Fick’s first law, the quantity of NO 2 − and 4- pyridylaldehyde in the sampler is proportional to the concentration outside the sampler, the diffusion coefficient, the dimensions of the sampler and the sampling time. Concentrations are calculated from the quantity of nitrite or 4-pyridylaldehyde captured in the sampler by means of Eq. 1: m z m C( gm ) 10 10 AtD Q t 3 6 6 k (1) Where the sampling rate Q k is constant:
Monitoring Studies of Urban Air Quality in Central-Southern Spain Using Different Techniques 63 1 Qk ( mLmin ) 60xDx z A (2) C represents the ambient air NO 2 or O 3 concentration measured by the passive sampler (micrograms per cubic metre), m is the quantity of NO 2 or O 3 captured in the sampler (micrograms) and z, A, t and D denote the diffusion length (centimetres), cross-sectional area (square centimetres), sampling time (minutes) and diffusion coefficient (square centimetres per second), respectively. Exposure time to sample NO 2 and O 3 was in all points 7 days. Details of the extraction and analysis procedure of the samples are given in Martín et al., 2010 according with R&P-Co 2001. In all cases, three unused cartridges belonging to the same lot were treated in the same manner as the samples. Then, it was subtracted by the average blank value from the absorbance values of the samples. 2.2.3 Mobile air pollution control station A Mercedes Sprinter van was selected as rolling platform for the measuring equipment. The mobile air pollution control station is equipped with a vertical manifold that distributes the sample to all the analyzers, a multipoint calibrator (API, model 700) with an internal ozone calibrator and photometer, a zero air generator (API, model 701) and a meteorological station. Table 1 presents a list of the characteristics of the instruments and measured parameters including meteorological parameters. The methods used to analyze the different air pollutants are those used by the Air-Quality Networks and therefore, defined by the European Directive (2008/50/CE), as reference methods. The particulate matter analyzer is based on beta radiation absorption technique and has been designated by the American Environmental Protection Agency (EPA) as equivalent method for measuring the PM 10 fraction of suspended matter (EQPM-0798-122). The calibration of the photometer and flows of the calibrator and analyzers was made at the beginning of the measurement period by the accredited calibration laboratory of the manufacturer. More experimental details are described in Villanueva et al., 2010. Parameter Instrument Time resolution Detection limit O 3 API 400A 20 s 0.6 ppb NOx API 200A 20 s 0.4 ppb SO 2 , H 2 S API 100A 20 s 0.4 ppb CO API 300A 20 s 0.04 ppm BTX Syntech spectras GC 955 15 min 0.05 ppb for benzene PM 10 Met One BAM 1020 Temperature and humidity Met One HP043 Pressure Met One 091 Wind direction and speed Met One 50.5 Solar radiation Met One 595 Rain Met One RC15 1 h 10 s 10 s 10 s 10 s -- 1 g/m 3 -40ºC / 0% 0 mbar 0.5 m/s 0 W/m 2 -- Table 1. Monitoring instruments employed in the mobile monitoring platform.
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AIR POLLUTION - MONITORING, MODELLI
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Contents Preface IX Chapter 1 Urban
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Preface This book provides a compre
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AIR POLLUTION – MONITORING MODELLING AND HEALTH

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