Comparison of the ISCST3 wet deposition algorithm with algorithms previously in use
Conference
·
OSTI ID:351045
- S.A. Campbell Associates, Travelers Rest, SC (United States)
Risk assessments for sources of toxic air emissions are often driven by the indirect effects of gaseous and particulate matter deposited from the plume to sensitive receptors such as farms and lakes. The release of ISCST3 provided, for the first time, an EPA-sponsored method for estimating annual deposition of particulate contaminants from plumes. However, the ISCST3 algorithm differs in several important aspects from those recommended by Bowman and used in various risk assessments in the past. In particular, the ISCST3 approach does not recognize the difference between short, intense precipitation events and long periods of moderate precipitation. This simplification is necessary to allow use of the hourly precipitation amount data which NWS presently collects. However, the effect of this change on deposition projections is unknown. An experimental comparison was made between the ISCST3 algorithm and older deposition models for five generic sources. The base model was a version of ISCST2 (called WETISC) which allows the user to specify scavenging coefficients for three size classes and three degrees of rainfall intensity. Two published sets of scavenging coefficients were used in the older model: those recommended by Bowman for general scavenging and those recommended by Zankel for below-cloud scavenging. For ISCST3, scavenging coefficients were estimated as recommended in the ISCST3 User`s Guide. Finally, the ISCST3 coefficients were used to estimate a set of coefficients for use in the ISCST2 model. All models were exercised using data from the DEPTEST.MET meteorological data set supplied with ISCST3.
- OSTI ID:
- 351045
- Report Number(s):
- CONF-970677--
- Country of Publication:
- United States
- Language:
- English
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