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Title: Uncertainty for data with non-detects: Air toxic emissions from combustion

Abstract

Air toxic emission factor datasets often contain one or more points below a single or multiple detection limits and such datasets are referred to as 'censored.' Conventional methods used to deal with censored datasets include removing non-detects, replacing the censored points with zero, half of the detection limit, or the detection limit. However, the estimated means of the censored dataset by conventional methods are usually biased. Maximum likelihood estimation (MLE) and bootstrap simulation have been demonstrated as a statistically robust method to quantify variability and uncertainty of censored datasets and can provide asymptotically unbiased mean estimates. The MLE/bootstrap method is applied to 16 cases of censored air toxic emission factors, including benzene, formaldehyde, benzo(a)pyrene, mercury, arsenic, cadmium, total chromium, chromium VI and lead from coal, fuel oil, and/or wood waste external combustion sources. The proportion of censored values in the emission factor data ranges from 4 to 80%. Key factors that influence the estimated uncertainty in the mean of censored data are sample size and inter-unit variability. The largest range of uncertainty in the mean was obtained for the external coal combustion benzene emission factor, with 95 confidence interval of the mean equal to minus 93 to plus 411%.

Authors:
;  [1]
  1. CALTECH, Pasadena, CA (United States). Division of Chemical & Chemical Engineering
Publication Date:
OSTI Identifier:
20823929
Resource Type:
Journal Article
Resource Relation:
Journal Name: Human and Ecological Risk Assessment; Journal Volume: 12; Journal Issue: 6
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; EMISSION; TOXIC MATERIALS; AIR POLLUTION; DATA ANALYSIS; DATA PROCESSING; COAL; FUEL OILS; WOOD WASTES; COMBUSTION; SIMULATION; URBAN AREAS

Citation Formats

Zhao, Y.C., and Frey, H.C.. Uncertainty for data with non-detects: Air toxic emissions from combustion. United States: N. p., 2006. Web. doi:10.1080/10807030600977178.
Zhao, Y.C., & Frey, H.C.. Uncertainty for data with non-detects: Air toxic emissions from combustion. United States. doi:10.1080/10807030600977178.
Zhao, Y.C., and Frey, H.C.. Fri . "Uncertainty for data with non-detects: Air toxic emissions from combustion". United States. doi:10.1080/10807030600977178.
@article{osti_20823929,
title = {Uncertainty for data with non-detects: Air toxic emissions from combustion},
author = {Zhao, Y.C. and Frey, H.C.},
abstractNote = {Air toxic emission factor datasets often contain one or more points below a single or multiple detection limits and such datasets are referred to as 'censored.' Conventional methods used to deal with censored datasets include removing non-detects, replacing the censored points with zero, half of the detection limit, or the detection limit. However, the estimated means of the censored dataset by conventional methods are usually biased. Maximum likelihood estimation (MLE) and bootstrap simulation have been demonstrated as a statistically robust method to quantify variability and uncertainty of censored datasets and can provide asymptotically unbiased mean estimates. The MLE/bootstrap method is applied to 16 cases of censored air toxic emission factors, including benzene, formaldehyde, benzo(a)pyrene, mercury, arsenic, cadmium, total chromium, chromium VI and lead from coal, fuel oil, and/or wood waste external combustion sources. The proportion of censored values in the emission factor data ranges from 4 to 80%. Key factors that influence the estimated uncertainty in the mean of censored data are sample size and inter-unit variability. The largest range of uncertainty in the mean was obtained for the external coal combustion benzene emission factor, with 95 confidence interval of the mean equal to minus 93 to plus 411%.},
doi = {10.1080/10807030600977178},
journal = {Human and Ecological Risk Assessment},
number = 6,
volume = 12,
place = {United States},
year = {Fri Dec 15 00:00:00 EST 2006},
month = {Fri Dec 15 00:00:00 EST 2006}
}
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  • This report addresses the key air toxic emissions likely to emanate from continued and expanded use of domestic coal. It identifies and quantifies those trace elements specified in the US 1990 Clean Air Act Amendments, by tabulating selected characterization data on various source coals by region, state, and rank. On the basis of measurements by various researchers, this report also identifies those organic compounds likely to be derived from the coal combustion process (although their formation is highly dependent on specific boiler configurations and operating conditions).
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  • Since passage of the Clean Air Act, ABB has been actively developing a knowledge base on the Title III hazardous air pollutants, more commonly called air toxics. In addition to design experience and database acquired in Europe, ABB has conducted source sampling and analysis at commercial installations for hazardous air pollutants to determine the emission rates and removal performance of various types of equipment. Several different plants hosted these activities, allowing for variation in fuel type and composition, boiler configuration, and air pollution control equipment. This paper discusses the results of these investigations.