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Asthma in Children: A Community-based Intervention Project
EPA Grant Number: R826708C001Subproject: this is subproject number 001 , established and managed by the Center Director under grant R826708
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: CECEHDPR - University of Southern California
Center Director: Gong, Henry
Title: Asthma in Children: A Community-based Intervention Project
Investigators: Gong, Henry , Jones, Craig , McConnell, Rob
Current Investigators: Gong, Henry , Diaz-Sanchez, David , Jones, Craig , McConnell, Rob
Institution: University of California - Los Angeles
EPA Project Officer: Fields, Nigel
Project Period: January 1, 1998 through January 1, 2002
Project Amount: Refer to main center abstract for funding details.
RFA: Centers for Children's Environmental Health and Disease Prevention Research (1998)
Research Category: Children's Health , Health Effects
Description:
Objective:(1) To design a carefully-controlled experiment for deposit accumulation and HC emission measurement. (2) To assess the effects of combustion chamber deposits on the hydrocarbon emissions from a modern production spark-ignition engine. (3) To measure the effect of CCD on HC emissions from single-component fuels. (4) To develop and validate a model for the mechanism(s) by which combustion chamber deposits lead to additional HC emissions. (5) To study the effects of combustion chamber deposits on NOx emissions.
Rationale: Engine deposits (on intake valve and combustion chamber) increase HC emissions. Some recent data suggest that combustion chamber deposits also increase NOx emissions. To meet stringent future emissions standards, the emissions due to deposits will have to be reduced. The first step towards that end is to better quantify these emissions and understand the mechanisms involved in their formation.
Approach: A four-cylinder, DOHC Saturn engine has been subjected to a standardized deposit build-up cycle. An additized fuel (which keeps the intake valves and ports clean) was used to isolate the effects of the combustion chamber deposits on emissions. HC and NOx emission measurements were taken continuously during the deposit accumulation process. In parallel a model for the effect of deposits on HC emissions has been developed.
Status: The project has now been completed. Four deposit build-up tests (100, 50, 25, and 35-hour tests) were carried out. In these tests, the HC emissions stabilized after about 25 hours. The HC emissions increased by an average of 14% due to deposit build-up. The HC emissions returned to the clean engine baseline levels after the combustion chamber deposits were removed. The NOx emissions, which were expected to increase slightly during these tests, showed substantial scatter and no clear trend was apparent.
The deposit accumulation process developed has shown that deposits can be built up systematically and reproducibly in engine dynamometer tests. The HC emissions trends were surprisingly repeatable. The significant finding was that the HC emissions increased for the first 20 hours of operation and then stabilized, even though deposits continued to build up. Thus engines will have to be very "clean" to largely eliminate this increase--an important practical issue. The NOx emission variability noted above is believed due to variability in the engines EGR system. Despite efforts to reduce this, no clear trends as deposits build up could be determined.
A model has been developed to explain the observed increase in HC emissions as deposits build up, and the lack of sensitivity of this increase to fuel compound in the individual hydrocarbon fueled tests. Critical to the development of this model were studies of the pore size distributions of the cylinder head and piston crown deposits (which had different characteristics).
Three different mechanisms were examined to explain the effect of CCDs on the HC emissions. The first is the displacement of fuel-air mixture into and out of the larger deposit pores as the cylinder pressure rises and falls. The second consists of pressure driven bulk flow into the deposit pores, in the pore size range (1 - 0.1 micrometer ) where viscosity is important. The deposits are treated as a porous medium with an estimated permeability. Darcy?s Law for flow in a porous medium forms the basis of this model. The third mechanism consists of ordinary diffusion of fuel molecules into the air (or exhaust gases) in the deposit pores. The fuel molecules diffuse into the deposit pores during the intake, compression, and combustion processes and get released into the combustion gases during the expansion and exhaust processes. During flow in, they are absorbed onto the pore surfaces. By applying these models to the appropriate pore size range, and weighting the trapped HC by the relative importance of these size ranges, the individual mechanism contributions to the total deposits impact was quantified. Only the crevice model of the larger (< 1 micrometer ) pores is significant, and the cylinder head deposits contribute many times what the piston deposits contribute. The model indicates that the pore depth to which fuel penetrates becomes limiting ( ~ 100 micrometer for the cylinder head) even though the deposit thickness steadily increases beyond that.
The maximum amount of HC trapped in the deposits is reduced by oxidation and retention in the cylinder. Allowing approximately for these effects produces estimates of the increase in engine HC emissions comparable to the measured increases.
Key Personnel
Graduate Student: Haissam Haidar Asthma is the most common chronic disease in childhood. Asthma is now associated with increasing frequency, hospitalization, and mortality, especially in nonwhite, poor, inner-city children. Research is needed to develop and evaluate comprehensive community-based programs designed to reduce asthma triggers in the home environment, such as house dust mites and cockroaches. In this study, inner-city, primarily minority, children with asthma are being
identified through a school-based mobile asthma clinic, the Breathmobile, which delivers high quality asthma care to these children. Working with school nurses and community organizations and 3 Breathmobile units, we propose a community-based intervention aimed at reducing asthma triggers in the home. The major goal of this study is to determine whether a comprehensive environmental health education program, enhanced by least-toxic integrated pest management for cockroach control, will result in reduction of dust mites or cockroaches in children's homes and clinical improvement in asthma.
Publications have been submitted on this subproject: View all 11 publications for this subproject | View all 80 publications for this center
Journal Articles:Journal Articles have been submitted on this subproject: View all 9 journal articles for this subproject | View all 50 journal articles for this center
Supplemental Keywords:asthma, children, health, air, exposure. , Air, Scientific Discipline, Health, RFA, Susceptibility/Sensitive Population/Genetic Susceptibility, Biology, indoor air, Risk Assessments, genetic susceptability, Health Risk Assessment, Children's Health, Atmospheric Sciences, Environmental Chemistry, Allergens/Asthma, adolescents, exposure assessment, asthma indices, allergen, health effects, indoor air quality, dust , air quality, dust mite, indoor environment, childhood respiratory disease, dust mites, harmful environmental agents, sensitive population, toxics, cockroaches, community-based intervention, respiratory, sensitive populations, biological response, air pollution, children, exposure, children's vulnerablity, minority population, school based study, asthma triggers, Breathmobile, asthma, human exposure
Progress and Final Reports:
2000 Progress Report
2001 Progress Report
2002 Progress Report
Final Report
Main Center Abstract and Reports:
R826708 CECEHDPR - University of Southern California
Subprojects under this Center:
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R826708C001 Asthma in Children: A Community-based Intervention Project
R826708C002 Children's Exposure to Environmental Tobacco Smoke: Changes in Allergic Response
R826708C003 Respiratory Disease and Prevention Center