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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}
}