Laserfiche WebLink
<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />the manifold to the SF6 analyzer indicated less than a half second residence time. Therefore, no time lag was <br />imposed on the SF6 data. <br />Estimates of IN concentrations can be made using SF6 if the dilution factor for SF6 is the same as for AgI <br />from a source collocated at the same site. This assumes that scavenging and sedimentation processes are negligible <br />or similar for the two substances. Equation (3) below was used to estimate concentrations of AgI. <br /> <br />X =1.7567X10-gQAgI fp <br />AgI QSF6 (T+27 3) <br /> <br />(3) <br /> <br />The source strength of AgI and SF6 are ~gl and 0s1'6 (mass per time). The concentration of SF6 is f which is <br />expressed in ppt by volume. The ambient pressure, p, is in mb and T is oC. <br />d. Calculating Airborne AgI Plume Positions <br />The acoustic IN detector's response is lagged due to delays caused by plumbing and the time needed to <br />grow acoustica1ly-detectable crystals ( ~ 20 )lID). The response is also smoothed because of mixing within the cloud <br />chamber. Heimbach et al. (1978) has shown a method to estimate the machine-induced variance which quantifies <br />this smoothing; however, it is not possible to pin this down exactly, particularly with the sparse IN concentrations <br />found at flight level. The plume edge, on the other hand, can be more accurately determined from time to first <br />response, and the artificial smoothing need not be estimated. Since the flights consisted of pairs of passes in opposite <br />directions, estimates of horizontal extent of IN could be made using pairs of plume edges. <br />A series of ground tests and airborne sampling of co-released AgI and SF6 plumes were used to estimate <br />the lag time to plume edge function. For the former, AgI samples were input at the humidifier on the IN detector. <br />The time of input and time interval to first response were recorded by hand and by the data acquisition system <br />(DAS). These tests were done on 23 January and 19 February 1991. For the airborne lag calibration points, it was <br />assumed that the co-released SF6 plume encounters had a negligible instrument response lag. Measurements of the <br />plumbing leading in from the aircraft's manifold indicate that the transient time to both instruments was far less than <br />the 1 s resolution of the DAS. Therefore, the lag of the IN detector could be assumed to be entirely machine- <br />induced. The final airborne calibration points were taken from the flights of 26 January, 17 February, and 13 and <br />14 March 1991. <br />Previous work by Super et al. (1988) suggests that the lag time to plume edge is a power function of the <br />sum of IN counts for the entire plume penetration. Three definitions of plume edge were tested using ground tests <br />and carefully selected airborne penetrations of co-released plumes: <br /> <br />-9- <br /> <br />