| Asthma is the most common chronic disease of childhood, bringing significant burden on child's health status. Indoor environmental exposures such as airborne particulate matter (PM) and environmental tobacco smoke (ETS) play a substantial role in asthma aggravation. Free-standing HEPA filters have been widely used for indoor PM control, but few studies have assessed the effectiveness of filters, and factors affecting filter performance. The assessment of promising approaches to reduction of indoor PM by air filter and further exploration of causal pathways in which children's asthma related health still needs to be improved. In China, studies have focused on the influence of outdoor PM concentrations on asthma symptoms; indoor PM studies are mainly about measurements and simulations on its concentrations and distributions. Strategies such as the use of air filter to reduce children's exposure to the airborne PM as a part of an epidemiological study have rarely been conducted. This study was motivated by the need to understand the key factors in effectiveness of interventions using free-standing HEPA filters for indoor PM control in households of children with asthma. This research includes the following:(1) Characterize indoor PM by the presence, if any, of HEPA filters, interventions, air conditioner, ETS exposure, short/long term though filed studies and experiments.126 low income households of children with asthma were recruited and randomized into one of three groups:a control group receiving only community health worker (CHW) home education visits (n=37); the standard intervention group receiving a free-standing HEPA filter (HEPA filter), and CHW visits (n=47); and an enhanced intervention group receiving the HEPA filter, the CHW visits, plus an air conditioner (n=42). After a household inspection and child's caregiver survey, each household received a baseline visit and seasonal visits (346 weeks in all). The measurements included PM, particle number counts (PNCs) in 0.3-1.0μm and 1.0-5.0μm dia size ranges, carbon dioxide (CO2), temperature, relative humidity and HEPA usage, ETS tracers, and air exchange rates (AERs). Participants were blinded to the filter use measurements during both sampling week and inter-season periods. The results showed that the PM concentrations differed significantly by HEPA filter intervention, groups and seasons; the ETS contributions to PM exposures remained about the same in different groups and intervention periods, by an average of 12-15μg m-3.(2) Evaluate the effectiveness of HEPA filters in reducing PM concentrations and factors affecting the performance by simulation models. The results showed that PM removal rates were quite similar to rates found in the field, with a range of 55-95%; filter air flow, room volume and AERs were the key parameters affecting PM removal.(3) Characterize the PM levels over the study period, understand the patterns of filter use and gather information from home characteristics and caregiver survey and the reasons for why persons might not use filters from a focus group. During weeks when air quality was monitored, filters reduced PM levels in the child's bedroom by an average of 50%. PM concentrations showed seasonal effects in different groups and differed before and after filter deployment, and ETS contributed PM levels significantly. Filter usage is a key factor in exposure and epidemiological studies using filter interventions. Cost and noisy were main reasons for low usage.(4) Characterize AERs and inter-zonal air flows, explore the sensitivity of mixing and transport on localized sources in residences, and the effectiveness of HEPA filter and factors affecting the PM distributions. AERs in homes and children's bedrooms showed significant seasonal differences and statistically significant correlated with house/bedroom volume, central air conditioner, any smokers indoors, number of smokers, number of bedrooms, CO2 and VOC concentrations. Two zone models showed that PM concentrations depended on emission rates, filter air flow, air flows from outdoor, volume, deposition rates and interzonal air flows. (5) Assess the effectiveness of interventions and identify the determining factors. General estimating equation (GEE) models were used to evaluate the effects of standard and enhanced interventions, differences between standard and enhanced interventions, and investigate whether central air conditioners altered effects of filters and distinguish effects of the standard and enhanced interventions. The results showed that HEPA filters could dramatically reduce indoor PM levels. Filter effectiveness was maintained in homes with central air conditioning; installation of a room air conditioner and filter in the bedroom in the enhanced intervention group did not yield improvements beyond that obtained by providing the filter alone. The effectiveness of HEPA filters depends strongly on outdoor PM levels, season, AERs, ETS, filter usage, the number of children and pets, temperature and relative humidity, as well as occupant behavior and the heating and ventilation system.This study has assessed the effectiveness of interventions using free-standing HEPA filters for indoor PM control in households of asthmatic children and identified the determining factors. Our approach and sample size obtained representative and robust results, which not only have helped to guide the development of active interventions but also be helpful and useful in research to improve asthma health status for children in China.
|
PDF Full Text Request