Treatment of losses of ultrafine aerosol particles in long sampling tubes
نویسندگان
چکیده
Abstract 7 Long sampling tubes are often required for particle measurements in street 8 canyons. This may lead to significant losses of the number of ultrafine (those below 9 100 nm) particles within the sampling tubes. Inappropriate treatment of these losses 10 may significantly change the measured particle number distributions (PND), because 11 most of the ambient particles, by number, exist in the ultrafine size range. Based on the 12 Reynolds number (Re) in the sampling tubes, most studies treat the particle losses using 13 the Gormley and Kennedy (1949) laminar flow model or the Wells and Chamberlain 14 (1967) turbulent flow model. Our experiments used a particle spectrometer with 15 various lengths (1.00, 5.47, 5.55, 8.90 and 13.40 m) of sampling tube to measure the 16 PNDs in the 5–2738 nm range. Experiments were performed under different operating 17 conditions to measure the particle losses through silicone rubber tubes of circular 18 cross–section (7.85 mm internal diameter). Sources of particles included emissions 19 from an idling diesel engine car in a street canyon, emissions from a burning candle 20 and those from the generation of salt aerosols using a nebuliser in the laboratory. 21 Results showed that losses for particles below 20 nm were important and were largest 22 for the smallest size range (5–10 nm), but were modest for particles above 20 nm. In 23 our experiments the laminar flow model did not reflect the observations for small Re. 24 This may be due to the sampling tubes not being kept straight or other complications. 25 In–situ calibration or comparison appears to be required. 26
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تاریخ انتشار 2008